A
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Annual Average Daily Traffic is the average of daily
(24-hour) traffic volumes at a specified point over a year. Average Daily Traffic
(ADT) is the corresponding average for a period less than a year (appropriate
where traffic volumes fluctuate significantly over time).
|
|
American Association of State Highway and
Transportation Officials represents state transportation departments
in fostering the development, operation, and maintenance of an integrated national
transportation system (formerly AASHO)
[ web ].
|
|
The "California Global Warming Solutions Act of 2006" is a comprehensive program
of regulatory and market mechanisms designed to achieve a 30 percent reduction
of greenhouse gases by 2020 (see SB 375)
[ web ].
|
|
A mode alternative defined only by objective characteristics. Also, a
(typically direct demand) mode choice model that
represents modal attributes relative to the best or average mode and has
only generic variables and parameters, facilitating
the introduction of new mode alternatives by obviating model re-estimation.
|
|
The right to enter and leave a location, facility, or service from a public
right-of-way. Accessibility is typically defined as a
measure of the ability of individuals or groups to exercise access.
|
|
Access defines movement toward and egress defines movement from, as in access/egress
to and from a development site or access/egress modes associated with getting to a
transit stop (an access point reached, for example, via car as an access mode) and
from the transit stop (an egress point) to a destination (via an egress mode, such
as walking). See line-haul.
|
|
Policies to "limit and consolidate access along major roadways, while promoting a
supporting street system and unified access and circulation systems for development"
(TRB) to promote safe operations and aesthetic design
[ web ].
|
|
[1] A measure of the ability of individuals to travel between various
activity locations within a region (see mobility);
[2] An aggregate measure of the relative accessibility of a location
to all other locations, often weighted by the number of opportunities
for a particular activity type and represented by a variety of indices.
|
|
Programs and policies for encouraging walking, biking, and other modes requiring
physical exertion directed toward achievement of sustainable travel, land use,
lifestyle, and health goals and objectives.
|
|
An activity occurs at the end of every trip and reflects
the trip purpose, that is, what the tripmaker did at the trip
destination. Activities are categorized according to
schemes such as subsistence/maintenance/discretionary or work/shop/social/etc.
The term is also used to describe the corresponding aggregate pattern of activity
in time and space.
|
|
A set of activities planned by an individual or a household during a defined
period of time.
|
|
A generic name for the study of activity and travel behavior,
often called the activity-based approach.
|
|
A modeling perspective focused on activities and reflecting the
generally held belief that travel is a demand derived from activity participation.
Activity-based models address individual and household travel /
activity patterns that summarize the scheduling of travel and
activities over the course of one or more days.
|
|
A model focused on activities rather than the conventional
trip-based approach. The complexity of true activity-based
models is such that they are still limited to research and controlled studies,
but tour-based models are entering practice (circa 2010).
|
|
An area characterized by concentrated activity and a high density of
trip ends, including the conventional CBD
and major retail, employment, or mixed-use developments.
|
|
In Transportation Systems Analysis, activity location functions
represent the relationship between the location of activity (land uses) and general
levels of prices for goods and services as well as the output levels of performance
and demand. Location functions are used to project the future activity
system in a region.
|
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An activity pattern (AP) is a full description of the travel and activities
completed by an individual (IAP) or a household (HAP) during a defined period of
time, including spatial, temporal, interpersonal, and transportation attributes.
It is the output of individual and household decision-making processes acting on
an activity program and reflecting potential stochastic
events that alter plans and constraints. The AP is the
revealed outcome of unrevealed behavioral processes. Activity pattern is
also used to describe the aggregate pattern of travel or activity in a population.
|
|
In most cases, synonymous with agenda, a set of activities
planned by an individual or a household during a defined period of time (often
this period is taken as one day).
|
|
In the Manheim/Florian framework for transportation systems analysis,
the Activity System constitutes a region's land uses and
activities, excluding only the Transportation System.
The Activity System in defined by location functions
and is a key element in defining demand functions.
|
|
A traffic control system where signal indications are determined by detection
of vehicle or pedestrian arrivals at a sensor. When only selected movements are
controlled by detection, the control is semi-actuated
(see fixed time and adaptive control).
|
|
See Americans with Disabilities Act of 1990 (ADA).
|
|
A traffic control system where signal control parameters are adjusted in realtime
based on ambient traffic measurements.
(see fixed time and actuated control).
|
|
An N nodes by N nodes network topography
matrix where cell (i,j) is non-zero if link (i,j) exists.
The cell value is set equal to one to indicate a link exists but it can be used
to store capacity or another link characteristic.
|
|
Alternate Fuel Vehicle (see AFV).
|
|
A 1992 UN action plan regarding sustainable development,
incorporating economic, environmental, public health, and other dimensions.
|
|
A (software) process to transparently act for a user by completing
transactions, seeking information of specific interest, or communicating
with other users and agents.
|
|
A computational process modeling approach for simulating
the actions of autonomous agents, an approach well-suited
for integrating learning and adaptation behaviors in
activity-based models.
|
|
Economic activity clustered in or around a single location. An agglomeration
economy is a benefit that accrues due to being part of an agglomeration.
|
|
A model with units of analysis defined as aggregates of the basic behavior units.
In travel forecasting, the basic behavioral unit is the individual decision-maker
or the household. In aggregate travel forecasting models, these basic units are
aggregated to spatially-defined Traffic Analysis Zones (TAZs)
(see also Disaggregate Models).
|
|
The process of obtaining aggregate forecasts (such as link flows or modal
shares) from disaggregate models. Techniques include naive
aggregation and sample enumeration.
|
|
Analytical Hierarchy Process (see AHP).
|
|
Automated Highway System (see AHS).
|
|
Artificial Intelligence, a multidisciplinary field dedicated
to the development of methods or models that emulate human reasoning.
|
|
A integrated suite of traffic microsimulation and
travel forecasting software. Developed by TSS
[ web ]. Other traffic microsimulation
packages include CORSIM, Cube Dynasim,
Paramics, SimTraffic,
TransModeler, and VISSIM.
|
|
The presence of one or more contaminants in the atmosphere in sufficient
quantity and/or for sufficient duration to potentially impact human and/or
environmental health. EPA defines standards for seven such
criteria pollutants, including ozone,
carbon monoxide, nitrogen oxides,
particulate matter, and sulfur oxides
[ web ].
|
|
An assessment of the presence in the atmosphere of defined pollutants,
including carbon monoxide, nitrous oxides,
particulate matter, and sulphur oxides.
Air quality modeling is a critical task in
metropolitan transportation planning for
regions that have not attained national ambient air quality standards
(NAAQS).
|
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A regional agency that adopts regulations to meet state and federal air
quality standards.
|
|
Application of mathematical models for the estimation of emission rates,
emissions by pollutant, dispersion of pollutants, and/or related air quality
characteristics, typically applied as post-processors to
the standard four-step model.
|
|
A modification of Davidson's link performance
function that reflects the original queueing theory elements but is amenable
to application with standard iterative assignment algorithms
(see also BPR).
|
|
Asservissement Lineaire d'Entree Autoroutiere,
Papageorgiou's (1991) efficient, local feedback control, ramp metering algorithm.
|
|
A systematic, computational methodology for finding solutions to mathematical
problems (e.g., the Frank-Wolfe Algorithm;
Dijkstra's Algorithm; Dial's Algorithm).
|
|
(AON) An elementary, deterministic trip assignment where the total
trips between an origin and a destination are loaded on a single (typically) minimum
travel time path. Link congestion effects are not considered, as compared with
capacity restrained or equilibrium assignment
(see also stochastic assignment).
|
|
The portion of a cycle for which all signal
indications display red, providing a
clearance interval for the intersection.
|
|
An advanced software package for the estimation of logit models. Developed by The Hague
Consulting Group [ web ].
|
|
A motorized vehicle that does not use gasoline or diesel fuels, instead using
natural gas, methanol, hydrogen, and related fuels, or electric-powered.
|
|
An option in a choice set, such as a mode choice alternative.
In the context of travel forecasting, a transportation system
alternative representing a future combination of current and planned system
elements under consideration in a transportation planning study.
|
|
Non-automotive modes of travel including public transportation
options and non-motorized modes such as bicycles and walking. Also includes evolving
modes such as Segways and electric scooters that can utilize walkways and bikeways.
|
|
Under SB375, California MPOs must
submit a Sustainable Communities Strategy (SCS)
as part of the Regional Transportation Plan (RTP). The
SCS must meet emission reduction targets if feasible to do so; if not,
the MPO develops a separate plan, an Alternative Planning Strategy,
that identifies impediments and a process to achieve targeted reductions
if the impediments were not present.
|
|
Alternative-specific indicates a variable or constant that is assigned to a
particular choice alternative in a utility
model. An alternative-specific constant takes on a value of one for the assigned
choice and its estimated parameter is usually considered the constant itself.
Variables that are assigned to all alternatives in a choice set are deemed
generic.
|
|
In discrete choice models, an alternative-specific variable appears
in the utility function of a specific choice alternative with an independently estimated
coefficient (compare with generic variable).
|
|
Programs designed to reduce peak period work trips by having working hours start
and/or end earlier and/or later than conventional work hours, often paired with a
reduction in the number of work days. For example, four 10-hour work days (versus
five 8-hour days) produce two fewer weekly commute trips
(trip reduction) and the remaining trips may be shifted
outside of the peak (peak spreading).
|
|
A systematic analysis of the engineering and economic feasibility of transportation
system alternatives under consideration for a corridor or
region, a process required before federal support can be allocated.
|
|
The portion of a cycle for which signal
indications display amber (aka yellow)
alerting drivers that a signal indication is about to change (from
green) to red
(aka a change interval).
|
|
A new survey effort from the US Census Bureau to replace
the decennial census long form, the ACS is sent to
a small sample of the population on a rotating basis
[ web ].
|
|
The February 2009 Act that authorized $787 billion of public funds, including
$48 billion for transportation (including $27.5 billion for highways, $8.4
billion for transit, and $8.0 billion for high speed rail)
[ web ].
|
|
The Americans with Disabilities Act of 1990 defined federal requirements for
accommodating individuals with disabilities in public facilities, including
public transportation systems (terminals, vehicles, etc.).
|
|
The time period corresponding to the highest morning traffic volumes.
The AM-peak hour is the highest volume hour within the AM-peak period, which
is typically defined as a 2 to 4 hour-long period
(see midday, PM-peak, and
off-peak periods.
|
|
Association of Metropolitan Planning Organizations,
a non-profit organization that serves as a transportation advocate for
MPOs
[ web ].
|
|
The US domestic intercity rail service operated by
the National Railroad Passenger Corporation since 1970.
|
|
ANOVA is a standard statistical technique for analyzing the components of variation.
Among other applications, it is used with Category Analysis to
develop categories for variables in Trip Generation models.
|
|
A decision-making approach featuring an hierarchical structure of choice criteria
for the ranking of choice alternatives.
|
|
Artificial Neural Network (see Neural Network).
|
|
ANalysis Of VAriance (see ANOVA).
|
|
An Application Programming Interface is any software that
enables a program application to use utilities provided by another application.
For example, microsimulation models such as Paramics can
be extended with APIs for new ramp metering, actuated signal control, or
vehicle routing algorithms.
|
|
Forecasting or sensitivity analysis with a model that
has been estimated, calibrated,
and validated. In travel forecasting,
models are applied to predict or to investigate relationships between
travel demand, system performance,
and associated impacts for one or more defined system
alternatives.
|
|
A federal allocation of authorized funding that permits federal agencies
to obligate funds for specified purposes
(see also authorization).
|
|
American Public Transportation Association,
an organization that promotes the accessibility and availability of public
transportation [ web ].
|
|
Advanced Public Transportation Systems,
a component of Intelligent Transportation Systems.
|
|
American Public Works Association,
a professional association of public agencies and private companies
that promotes public infrastructure and services
[ web ].
|
|
Air Quality (see AQ).
|
|
Air Quality Management District
(see AQMD).
|
|
One of the most complete and extensible GIS available today.
ArcView and ArcInfo are functional implementations of ArcGIS software.
Developed by ESRI [ web ].
|
|
Point, line, and area sources
are idealized zero-, one-, and two-dimensional locations that are sources for
various pollutants. Small stationary and non-transportation pollution sources that
are not included as point sources are treated collectively
as area sources in estimating emissions.
|
|
Describes the type and density of development through which a roadway traverses.
In travel forecasting, facility type and
area type are used to create a look-up table that
provides default link speeds and capacities.
|
|
The US federal agency responsible for the planning, design, construction, and
operations of both civilian and military facilities maintains jurisdiction
over US domestic waters [ web ].
|
|
American Recovery and Reinvestment Act of 2009
(see ARRA, TIGER).
|
|
In the functional classification of roads, arterials are
traffic-controlled facilities that place relatively greater emphasis on service
to through traffic and less emphasis on serving local land uses than do
collectors and local streets.
Arterials are often sub-categorized (as major/minor or primary/secondary) although
specific operational characteristics vary over regions. Arterials and limited-access
facilities account for about 10 percent of the lane-miles
in the US, but almost 75 percent of the VMT. In travel
forecasting networks, major (or primary) arterials are virtually always coded,
as are typically minor (or secondary) arterials. A good rule of thumb in
network coding is to include functional classifications
one level lower than the level at which policy decisions will be made.
|
|
Generic term for trip assignment, transit or vehicle.
|
|
Advanced Traveler Information Systems.
Advanced technologies to provide real-time information
to travelers. A component of Intelligent Transportation Systems
(see ITS).
|
|
Advanced Transportation Management Systems.
Advanced technologies such as decision support systems (DSS),
sensors and control devices, vehicle tracking, video and other remote monitoring,
etc. to improve the efficiency of transportation operations. A component of
Intelligent Transportation Systems (see ITS).
|
|
Meeting or exceeding NAAQS standards for
criteria pollutants, including ozone,
carbon monoxide, particulate matter, and
nitrogen oxides. A region may be an attainment area
for a given pollutant and a non-attainment area for
other criteria pollutants
[ web ].
|
|
Attitudes describe an individual's state of mind, developed with experience,
that exerts a dynamic influence on individual behavior.
|
|
Survey data comprising individual self-assessments of attitudes with respect to
cognition (via level of importance) and affect (via comparative ranking such as
satisifaction level), including subjective attributes of a choice alternative
such as comfort or convenience.
|
|
The location or zone drawing a generated trip, and also used
for the attracted trip itself: a zone is an attraction
for N trip attractions. Contrast with production
and destination.
|
|
Same as Attraction Factoring.
|
|
When applying a singly-constrained gravity model for
trip distribution, the estimated attractions (column sums)
will not match inputs from trip generation. Attraction
Factoring is a technique to adjust the SCGM attractiveness term so that
estimated attractions in subsequent iterations converge to those from trip
generation (see also column & row factoring).
Note that this process is often referred to as "attraction balancing", which
can be confused with the balancing of attractions to match
productions after trip generation.
Wj(n+1) =
[ Ajobs / ΣiTijest(n) ]
Wj(n) , where Wj(1) = Ajobs
|
|
The loss of participants during the course of a study, often compromising
results or necessitating replenishing the sample.
|
|
Federal legislation that establishes the operation of a federal program
or agency for a particular type of funding obligation (ISTEA, TEA-21, etc.)
(see also appropriation).
|
|
An initial goal of intelligent transportation systems (ITS)
was dedicated highway lanes providing fully autonomous, computer-controlled
vehicle flow utilizing vehicle-roadway and inter-vehicle communications that
removes drivers from control decisions once their vehicles join a platoon on
the facility. Field demonstrations demonstrated the technical feasibility of
AHS to increase capacity by decreasing headways and flow perturbations,
but the AHS goal was eliminated in favor of semi-autonomous components
and vehicle-infrastructure integration (VII).
|
|
The degree to which an automobile is available to an individual
(compare to auto ownership). In general, vehicle
availability.
|
|
The number of motorized vehicles owned by or available to an individual or a
household. Vehicle availability is highly correlated with trip
generation and mode choice decisions, thus,
auto ownership models are developed as an important input
to travel forecasting.
|
|
A pre-processing step in most travel forecasting
models that produces estimates of auto ownership, a critical
variable in most trip production models. Category
models typically require distributions of households by level of auto
ownership (e.g., number of households with 0, 1, 2 or more cars per household).
|
|
An interoperable, distributed, transportation management system concept
featuring a mobile, ad-hoc, peer-to-peer network integrating vehicles,
information technology, and communication systems with transportation
infrastructure (developed at ITS, Irvine).
|
|
A video traffic detection system that automates the process of vehicle
detection and traffic data collection in lieu of loops
[ web ].
Similar systems include Vantage
[ web ].
|
|
In the relaxation of a non-linear program (e.g., UE), the
linearization using the gradient (e.g., AON) is deemed the
auxiliary problem and the results are the auxiliary flows.
|
|
A lane added to a freeway section to accommodate section-specific volumes
such as between an on-ramp and the next off-ramp, but also associated with
lanes designed for section-specific uses such as weaving or hill-climbing.
|
|
In trip assignment, the auxiliary problem is the
linear program (implemented as All-or-Nothing Assignment)
that is used as a convex combination with the current solution to determine a
new solution to the original non-linear UE problem
(see Frank-Wolfe).
|
|
Automatic Vehicle Control and Safety Systems,
a component of Intelligent Transportation Systems
(initially known as AVSC).
|
|
[1] The expected value of cost (see marginal cost).
[2] In travel forecasting, cost is usually taken as either
travel time or generalized cost for network links or O-D pairs. In the
trip assignment step, equilibrating average costs of
link performance functions yields a user equilibrium
result.
|
|
Automated Vehicle Identification.
|
|
Average Vehicle Occupancy is, for a given area and time period,
the total number of persons traveling in private vehicles divided by the total
number of private vehicles utilized (see also AVR).
|
|
Average Vehicle Ridership is, for a given area and time period,
the total number of persons traveling by any mode, divided by the total number of
private vehicles utilized (see AVO).
|
|
| B | [ back to top ] |
|
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A typical performance curve has travel time increasing at an
increasing rate as volume approaches capacity. Beyond capacity, congestion effects
begin to reduce output volume so the curve bends back toward lower volumes as
travel time continues to increase.
|
|
A holistic view of transportation systems in which multiple individual modes
jointly provide users with travel options, and for which system planning reflects
the relative individual and system level advantages of alternative modes.
|
|
See Trip Balancing.
|
|
For a defined sequence of coordinated traffic signals, the length of green
time during which vehicles leaving a signal will be able to reach subsequent
signals during their green phases.
|
|
A traffic signal phase where red is displayed to all vehicle movements, allowing
pedestrians to cross in all directions, including diagonally, simultaneously. Also
known as a Scramble Phase. Can lead to greater delay for
vehicular and pedestrian traffic by eliminating overlap phasing but may be appropriate
when there are large pedestrian volumes.
|
|
A unit of volume used in oil production and transportation equal to 42
US gallons (or 159 liters).
|
|
A reference point in travel forecasting, representing the current
state of the transportation and activity
systems plus projects that have already been programmed for implementation in the
forecast period, on which comparisons with future alternatives are based.
|
|
Employment directed toward addressing non-local (export) demands, such as
manufacturing, mining. and agricultural employment
(see service employment).
|
|
The objective function of the user equilibrium optimization
program, equal to the sum of the integrals of the link
performance functions, proposed by Beckmann, McGuire, and Winsten (1956).
|
|
The measurement of system performance outputs prior to an infrastructure or
service improvement followed by remeasurement after implementation, with any
performance changed attributed to the improvement. For certain projects, such
as those that entail longer implementation periods,
control samples may be required to ensure that factors
other than the improvement are not responsible for the performance change.
|
|
The observable outcome of an individual engaged in active decision-making
as a function of intentions, attitudes, and perceptions.
Short-term behavior includes activity and travel choices; long-term behaviors
include location, life style, and role choices.
|
|
A model that reflects the revealed outcome of individual decision processes
as a function of values, attitudes, and preferences.
|
|
A result of an action expressed in terms of the utility
gained from the action. In transportation, benefits are often expressed as
cost savings.
|
|
An evaluation technique that compares the societal benefits and costs, measured
in monetary terms, of proposed projects or policies. Alternative actions are
incrementally compared to find the greatest net benefits.
|
|
The ratio of a project's total benefits to total costs, measured in monetary
net present value. In benefit-cost analysis,
alternative projects are incrementally compared to find the greatest net benefits.
|
|
Projects or processes that exemplify the state-of-the-practice
in transportation planning, design, management, and operations, and that serve as
models of effectiveness for adoption consideration in related applications.
|
|
An estimator that does not tend toward the population parameter as
sample size increases.
|
|
Bid-rent theory, which underlies some land use models,
proposes that land uses organize geographically based on their capacity to
compete for land rents, a capacity controlled by economic aspects of the
land use demanded and accessibility to markets. Consumers bid for land at the
location that maximizes their utility at current market rents (the bid rent).
|
|
A generic but appropriate term for extremely large data sets associated with
innovative data management and analysis techniques used to reveal underlying
patterns and relationships. In human travel and activity behavior research
and analysis, Big Data can capitalize on independent but spatially and
temporally consistent data to identify statistical links, for example, between
anonymous, discrete cell phone use and locational-referenced socio-demographic
data, to estimate OD flows, travel times, and other system
attributes.
|
|
The moniker assigned to Boston's Central Artery Project that re-routed
I-93 under central Boston to address congestion but consumed 15 years and
$15 billion between 1991 and 2007, and incurred massive cost overruns and
construction problems.
|
|
A measure of efficiency for an algorithm's
computational complexity, providing a worst-case
"Order of" magnitude for the number of elementary computations.
In general, O(log(n)) < O(n) < O(nlog(n)) < O(n2) <
O(n3) < O(2n)
|
|
An optimization problem decomposed into a primary optimization problem with
one set of variables and constraints and a second problem, embedded in the
first, with a second set of variables and constraints. Applications include
dynamic traffic assignment.
|
|
A numerical root-finding algorithm that proceeds by halving the search
interval and evaluating the derivatives of the function at subinterval
endpoints. It is utilized in the Frank-Wolfe algorithm
to find the minimum of the Beckmann objective function
along the line between the current (convex combination)
and auxiliary (all-or-nothing) solutions.
|
|
In 1899, Henry Bliss became the first pedestrian fatality from an
automobile accident.
|
|
A standard spatial aggregation unit used by the U.S. Census,
typically corresponding to actual city blocks. Block data is aggregated into the
more commonly used census tracts.
|
|
A consensus-building program initiated in California at the regional level,
incorporating all stakeholders, and integrating land use,
transportation, and environmental planning in a visioning
process involving scenario building with measurable performance outcomes.
|
|
A short-range radio technology to standardize communications and data
synchronization between microprocessor applications, such as cell phones,
PDAs, and laptops, operating in the unlicensed 2.4 GHz frequency band.
|
|
A colloquialism for a typically public-funded project characterized by
continued or increasing expenditures while expected objectives are
decreasingly likely to be achieved, due to understated costs or overstated
performance projections (see success story).
|
|
A section of a transportation facility where capacity is
significantly lower than on the upstream section, restricting traffic
volumes and creating queues
(AKA chokepoint).
|
|
The theory due to Herbert Simon that rational (i.e., utility maximizing)
behavior is limited (bounded) because decision-makers consider only a restricted choice set
and a finite decision time and thus may satisfy rather than optimize their
choices. Compare with utility maximizing and satisficing
approaches.
|
|
The former US Bureau of Public Roads, now FHWA.
|
|
An empirically estimated and commonly utilized link performance function
developed by BPR for calculating travel time as a function of link
volume [ t = t0(1+α(vol/cap)β) ].
|
|
A counter-intuitive, theoretical state where, under
user equilibrium assignment, a network link addition can
produce an increase in the total cost of travel.
|
|
Abandoned industrial or commercial properties within urban areas where
redevelopment is complicated by environmental contamination.
|
|
Bus Rapid Transit (see BRT).
|
|
Bureau of Transportation Statistics
(see BTS).
|
|
The final completion of all elements of a planned project or system.
|
|
A department within USDOT responsible for the collection,
analysis, and reporting of transportation data
[ web ].
|
|
A Monte Carlo simulation-based trip assignment
algorithm that samples perceived link costs for different users from a uniform
distribution (Burrell, 1968).
|
|
A generic term for the operation of buses on dedicated roadways or in
restricted access lanes, with limited stops and often with signal
priority or preemption,
to emulate rail transit performance characteristics while maintaining
the flexibility and cost of bus transit.
|
|
| C | [ back to top ] |
|
|
The Clean Air Act of 1970 established national air quality
standards, defined criteria pollutants, and required
regions that do not conform to these standards to prepare
an SIP. The Clean Air Act Ammendments
(1977 and 1990) established criteria for attaining federal standards.
|
|
The Clean Air Act of 1970 established national air quality
standards, defined criteria pollutants, and required
regions that do not conform to these standards to prepare an
SIP. The Clean Air Act Ammendments
(1977 and 1990) established criteria for attaining federal standards.
|
|
Citizen Advisory Committee (see CAC).
|
|
Computor Aided Design is the application of
computer-based tools to facilitate design of systems and components
(also see CAE).
|
|
Computor Aided Engineering is the application of
information technology to the planning, analysis, and
design of engineering systems (also see CAD).
|
|
Corporate Average Fuel Economy Standards are
established by Congress and require vehicle manufacturers to produce new
vehicle fleets that meet a composite fuel economy standard for a given year.
|
|
The On-line California Freight Data Repository compiling a number of
freight-related data sources and documentation maintained by UC Irvine
[ web ].
|
|
Calibration, an exercise in goodness-of-fit, is the
fitting of a model to observed data, primarily by adjusting model parameters.
Calibration might:
(a) be performed following model estimation,
(b) involve a pre-specified model that uses transferred structure and parameters
(e.g., QRS), or (c) be linked with the process of model
validation. In travel forecasting,
models are typically calibrated every 10 years, corresponding to major regional
data collection efforts. Models are validated prior to any
forecasting application.
Note: In travel forecasting, the terms estimation and
calibration often have been used interchangeably. Determining the
structure of the model is explicitly part of the estimation process thus
lending it greater statistical formality, but both terms reflect the same
overall objective. If the structure of the model is pre-determined, then
perhaps calibration is the better term. If model specification is
involved, then perhaps estimation is the better term.
|
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A statewide freight forecasting model for the state of California
developed by UC Irvine (2011-2013) for Caltrans using state
and federal data (FAF) and linked to the
California Statewide Travel Demand Model.
|
|
A statewide travel forecasting model for the state of California
developed by UC Davis (2010-2012) for Caltrans and linked to
the California Statewide Freight Forecasting Model.
|
|
A state commission established in 1977 to advise and assist the California
legislature and Caltrans in implementing transportation
policy, establishing priorities, and allocating funds for transportation
investments, via the State Transportation Improvement Program
(STIP).
|
|
The California Transportation Plan (CTP) is the state's long-range transportation plan
(LRTP) that forms the blueprint to guide future transportation
decisions and investments to meet state goals and objectives
[ web ].
|
|
A GIS- and rule-based model of housing development
developed by Landis (1994), but not a general purpose land use model.
|
|
An air quality dispersion model designed to determine air pollution
concentrations near transportation facilities (incorporated into the
more refined CAL3QHC model). Developed by
Caltrans [
web ].
|
|
The California Department of Transportation, the state agency responsible for
design, construction, maintenance, and operations of designated California's
state and interstate highways, provides inter-city rail services, and works
with local agencies in all areas of transportation
[ web ].
|
|
A CALINE3 based CO model with a
traffic model to estimate queues and delays at signalized intersections.
|
|
The maximum sustainable flow (typically measured in vehicles per hour)
past a defined point (or over a uniform roadway segment) during a defined time period,
under prevailing traffic and roadway conditions (see also LOS).
|
|
Performance evaluation of roadway sections and
intersections to estimate the portion of
capacity that is utilized and the associated
level-of-service, under current or proposed scenarios.
Performance, a function of demand and
supply (incorporating characteristics such as
facility type, geometric design,
and traffic control), is defined by level-of-service,
cost, and capacity.
|
|
The general term "capacity restrained" (or capacity constrained) reflects
the increase in congestion as assigned link volume approaches link capacity.
This is reflected in most link performance functions (LPF).
The specific term "Capacity Restrained Assignment" (CRA) reflects procedures
that attempt to correct the inadequacy of All-or-Nothing
assignment to reflect congestion resulting from link capacity constraints.
CRA algorithms recompute link travel times using assigned volumes as input to
link performance functions. These times are used to recomputed minimum paths
for additional iterations of AoN assignment. Heuristics such as travel time
smoothing or link volume averaging were used in attempts to achieve convergence
to equilibrium conditions (see also UE).
|
|
The costs of infrastructure and long-term assets such as facilities, rights-of-way,
and vehicles. Compare with operating costs.
|
|
The process of project appraisal to determine the economic value of
proposed project alternatives with assessment techniques such as
net present value, equivalent annual cost,
or internal rate-of-return.
|
|
A microscopic theory of traffic flow based on the behavior
of a vehicle following a lead vehicle.
The General Motors car following models relate the acceleration at time
(t+Δt) of a vehicle following a leader as a function of spacing and speed
relative to the lead vehicle at time t, the following vehicle's speed at time
(t+Δt), and a sensitivity parameter.
|
|
An alternative to conventional individual ownership and use of motorized
vehicles where a private company, public agency, or cooperative manages a
fleet of vehicles that can be used by any registered members for any amount
of time. Usage entails a computer- or phone-based reservation system and
a keyless, smart card access to a reserved vehicle
located in a fixed parking space. See station car.
|
|
California Air Resource Board is a part of the
California Environmental Protection Agency and is responsible for statewide
air quality
[ web ].
|
|
A colorless, odorless, non-toxic gas resulting from the combustion of
carbon-based fuels. A normal component of air, CO2 is also a
greenhouse gas and a suspected causal agent in global warming.
|
|
A colorless, odorless, toxic gas produced by the incomplete combustion of
fuels. A criteria pollutant, over 80 percent of CO
is produced by gasoline-fueled vehicles.
|
|
A roadway lane dedicated for use by high-occupancy vehicles,
typically as a physically-separated lane on a freeway or other limited-access
facility.
|
|
Classification And Regression Trees are
nonparametric, hierarchical modeling techniques to determine
if-then conditions for the accurate classification of continuous or categorical
dependent variables with continuous or categorical explanatory variables.
|
|
A multi-agent, real-time decision support
expert system for congestion management that integrates
real-time traffic control and simulation
[ web ].
|
|
A mathematical theory that seeks to describe phenomena characterized by abrupt
changes that follow from continuous processes. The limited number of ways that
such changes can take place are defined as the elementary catastrophes.
|
|
Applies to a transportation project that has minimal environmental impact
and thus does not require an EIS.
|
|
A general statistical technique for exploring relationships among variables.
Discrete categories are specified for one or more explanatory variables and
then the mean of a dependent variable is computed over the observations in
each defined cell. Used extensively in trip generation for
household trip production models, this method is also
known as Cross Classification Analysis (compare with
regression).
|
|
Computer-Assisted Telephone Interview techniques
integrate computer-based surveys with human interviewers to facilitate survey
execution, coding, and error checking. Integration of GIS,
GPS, and computer-based self-administered surveys (such as
CHASE and REACT!) are evolving to
minimize interviewer requirements.
|
|
The Chicago Area Transportation Study, one of the
first comprehensive transportation studies, essentially introduced the basic
four step modeling paradigm in 1959
(CATS, the MPO for the Chicago region, merged into the
Chicago Metropolitan Agency for Planning in 2005).
|
|
A causal model provides a cause and effect versus a
correlative relationship. A causal variable is an
explanatory variable whose presence and value results
in a corresponding presence and a value for a dependent
variable.
|
|
Central Business District: The traditional downtown retail,
commercial, service, and institutional employment center of a metropolitan area.
|
|
California Center for Innovative Transportation,
the University of California's Caltrans-sponsored
center established to accelerate the implementation of research results and
technologies [web ].
|
|
Closed Circuit TeleVision utilizes cameras and fiber
to transmit realtime video to traffic management centers for traffic surveillance.
|
|
An n-dimensional array of identical finite state cells whose state evolution
is rule-based, defined by the current state of the cell and of its neighbors.
CA form the basis of a class of simulation models from which complex
macroscopic behavior can emerge using simple microscopic
rules (examples include pedestrian and vehicle traffic behavior).
|
|
The process of collecting, compiling, and disseminating demographic,
economic, and social data describing a defined population at a specific time.
|
|
[1] The decennial enumeration of the U.S. population including
the Journey to Work (JTW),
the American Community Survey (ACS), and
the Public Use MicroSample (PUMS);
[2] The U.S. Census Bureau [ web ];
[3] The Census Transportation Planning Package
(CTPP).
|
|
A division of a census tract representing the smallest
geographic unit for which the Census tabulates
population-level data. The size distribution ranges from individual city blocks
in dense urban areas to very large areas in rural or other low density areas.
|
|
The US Census Bureau and the Office of Management and
Budget define Metropolitan Statistical Areas as core areas of substantial
centralized population and the adjacent economically and socially integrated
areas. Terminology has evolved from Standard Metropolitan Area (SMA), to
Standard Metropolitan Statistical Area (SMSA), to Metropolitan Statistical
Area (MSA), to the current (2000) Metropolitan Area (MA, which are either
spatially distinct MSAs or Consolidated MSAs (CMSA) that comprise two or
more primary MSAs (PMSA))
[ web ].
|
|
The US census aggregates household demographic
and socio-economic data by spatially defined units called census
tracts. Similar in design and spatial scale as TAZs, census
tracts are mapable to TAZs but are not identical.
|
|
The largest city in a metropolitan area
(see metropolitan classification).
|
|
One centerline-mile corresponds to a mile-long segment of a roadway, independent
of the number of lanes in either direction. One mile of 8-lane freeway and one
mile of 2-lane local street both are one centerline-mile of roadway. Total
centerline-miles is a measure of the spatial density of roadway infrastructure.
Compare to lane-miles.
|
|
Historically, metropolitan areas were defined by a single center, the
Central Business District (CBD) or traditional downtown.
With suburbanization, non-CBD activity centers developed.
These centers were compact areas characterized by higher density, often
mixed use development. While traditional centers were
typically served by multi-modal transportation
systems, new centers were more likely to be automobile dominated.
|
|
If a random sample of size N for variable X is drawn from a population with mean
μ and finite variance σ2,
then the sampling distribution of the mean of X will have mean
μ and variance σ2/N
and will tend toward normal as N becomes large.
|
|
A idealized location theory developed by Christaller (1933) that introduces a
hierarchy of goods and services based on accessibility to market populations,
resulting in a hexagonal distribution of cities, towns, and their
hinterlands. CPT is limited by simplifying
assumptions that are comparable to von Thünen's.
|
|
A defined point within a TAZ from which all trips are
assumed to start or end. It should be located to reflect the center of
activity in a TAZ and not necessarily the geographic center. Centroids are
connected to the network via centroid connectors,
abstract links that represent general access onto the formal network. Some
travel models load trips directly onto network links (such as
microsimulation models).
|
|
Abstract links that connect centroids to network
nodes and represent general access from a TAZ to the
formal transportation network.
|
|
The California Environmental Quality Act (1970)
that requires state and local agencies to identify and mitigate significant
environmental impacts, a process summarized in an EIR.
|
|
A trip chain: a sequence of tripstrips and
activities, typically starting and ending at home
(AKA tour). Trip chaining is the
process of linking travel between non-home activities to reduce overall travel
disutility.
|
|
An electronic sign used on roadways to provide travelers with information on
traffic conditions, special events, etc. (also known as Variable Message Sign).
|
|
A property of some dynamic systems that are highly sensitive to initial
conditions and produce seemingly random effects despite being deterministic.
See logistic model [2].
|
|
A collaborative work session in which stakeholders and
planning and design professionals draft potential solutions to a design problem,
increasingly used in land use and transportation planning.
|
|
Computerized Household Activity SchEduling
survey, the first essentially self-administered, PC-based
survey instrument to collect, process, and archive household travel/activity
diaries, developed by Doherty (1998) based on HATS
(see also REACT!).
|
|
A series of curb extensions on alternating sides of a road to narrow the perceived
lane width and calm traffic. Chokers are curb extensions
directly opposite each other, often at intersections
(see traffic calming).
|
|
CFCs are a family of gases containing chlorine, fluorine, and carbon, that
were used as coolants and contributed to ozone depletion.
|
|
Curb extensions directly opposite each other, often at intersections to narrow the
perceived lane width and calm traffic. A chicane is a series
of curb extensions on alternating sides of a road.
|
|
Choice-based sampling sets sampling rates differentially for choice alternatives,
which allows choices such as transit, which are selected less frequently, to be
sampled at a higher rate to provide sufficient choice observations. Model estimation
is made consistent by applying appropraite weights reflecting population shares.
|
|
The set of choice alternatives available to a decision maker. For example,
the choice set of modes available to a particular decision maker might be
car, bus, and walk.
|
|
A section of a transportation facility where capacity is
significantly lower than on the upstream section, restricting traffic
volumes and creating queues
(AKA bottleneck).
|
|
An element of a general plan that includes the general
location and characteristics of existing and proposed transportation faclities.
|
|
Public groups organized and utilized by MPOs and
transportation authorities for continuous citizen
input to the transportation planning process.
|
|
The process of optimizing metropolitan logistic
activities, in consideration of social, environmental, economic, financial,
and energy impacts of urban goods movement.
|
|
ASCE defines civil engineering as "the design and maintenance of public works
such as roads, bridges, water and energy systems as well as public facilities
like ports, railways and airports."
|
|
In transportation, Title VI of this federal legislation
ensures environmental justice in the location of transportation
infrastructure and for improvements in system performance.
|
|
A means of estimating multinomial probit (MNP) models that utilizes
an approximation, applied recursively, to obtain the approximate distribution of the
maximum of a number of normal variables, allowing for the estimation of MNP choice
probabilities. The method is efficient but is often limited in practical applications.
|
|
A government-industry partnership, sponsored by the US Department of Energy's
Vehicle Technologies Program, to reduce oil consumption in the transportation
sector by advancing the use of alternative fuels and vehicles technologies
[ web ].
|
|
A change in global or regional long-term climate patterns, due to increased
atmospheric carbon dioxide and other greenhouse gases,
with the combustion of fossil fuels believed to be a
major causal factor [ see global warming ].
|
|
A control system that feedbacks measured output to adjust the control strategy.
In an actuated control system, a control strategy is
implemented via field controllers while system detectors feedback performance
data to the control system. The advantage of closed loop control is that
disturbances (e.g., flow variations) can be accommodated by adjusting the
control strategy (compare with Open Loop System).
|
|
In the beginning there were a small number of massive but isolated mainframe
computers, where all hardware, software, and data (both system and user files)
were stored and accessible through remote terminals. Then came the Internet,
which provided high speed connections between mainframes. Simulaneously, the
introduction of Personal Computers (PCs) placed all software and data on
discrete hardware platforms, with these millions of hardware/software devices
soon also interconnected via the Internet. The cloud reassumes control
of software and data on a vaporous, distributed hardware "cloud" which includes
both system and user files, accessible by numerous individual devices such as
tablets, game consoles, and smart phones. Individuals will no longer own
software (nor necessarily own their user files) and will pay on essentially a
usage-based contract similar to smart phones, music streaming, and, as in the
beginning, vintage time-sharing mainframe computers.
|
|
[1] Critical Movement Analysis, a simplified approach to
assessing intersection capacity utilization based on traffic movement volumes
but independent of signal timing. See ICU.
[2] Congestion Management Agency, in metropolitan counties
in California, an agency responsible for the development and implementation of
a Congestion Management Program ( CMP ) required under Prop
111 since 1990.
|
|
Congestion Mitigation and Air Quality Program.
A Federal program for projects to reduce congestion and improve air quality
in regions that have not yet attained federal air quality standards.
|
|
Comprehensive Modal Emission Model is a
microscopic emissions model that estimates emissions
for light-duty vehicles as a function of the vehicle's operating mode and
is applicable to project-level or corridor-specific transportation control
measures. Developed by UC Riverside for NCHRP
[ web ].
|
|
Corridor Mobility Improvement Account
(see CMIA).
|
|
Congestion Management Plan (see CMP).
|
|
Changeable Message Sign (see CMS).
|
|
A production function relating level of production Q to the
input levels of the factors of production (capital K and labor L). A sample
Cobb-Douglas function is given by:
Q = c Ka Lb where a, b, and c estimated coefficients.
|
|
[1] See network coding;
[2] See survey coding.
|
|
A estimated parameter that modifies a variable in a model.
|
|
Council of Governments (see COG).
|
|
Information processing of spatial data, where an individual perceives,
contextualizes, and interprets relative locations and attributes of the
spatial environment.
|
|
Generically, a population subgroup homogeneous over specified characteristics.
In demographic models, a cohort is usually defined
by age and gender. In cohort component models,
cohort-specific birth, death, and migration are used to forecast population.
|
|
A population projection technique where population is split by gender and age
cohorts and differential birth, death, and migrations
rates are applied. Also called Cohort Survivor.
|
|
See cohort component models.
|
|
[1] A cold start occurs when a vehicle's engine is started more than an hour
after the previous period of operation (see hot start).
Cold start emission rates apply for the first 505 seconds after a cold start.
[2] The initial iteration of an algorithm such as trip assignment is considered
a "cold start" (see warm start).
|
|
In the functional classification of roads, collectors
serve a role mid-way between arterials and
local streets, placing similar weights on service to
through traffic and service to local land uses. As such, collectors serve
to channel arterial traffic to and from local streets. Collectors account
for about a quarter of the lane-miles in the US,
but less than 20 percent of the VMT. In travel forecasting
networks, the inclusion of collectors varies based on the scale and scope of
the model and the policies to be tested.
|
|
When applying a singly-constrained gravity model for
trip distribution, the estimated attractions (column sums)
will not match those from trip generation. Column and
Row Factoring uses iterative proportional fitting
to factor the estimated trip matrix so that the resulting productions and
attractions match corresponding values from trip generation
(see also attraction factoring).
|
|
[1] In large-scale network programming problems, most variables are non-basic
and equal to zero, yielding very sparse matrices. Column generation is a
bi-level solution approach of adding to the master problem
only those variables that are identified in the sub-problem as improving the
overall solution.
[2] The automatic process of identifying paths within an algorithm is referred to
as column generation because each new path generated adds a column to the
link-path incidence matrix
(see also path enumeration).
|
|
A commons is a shared resource (e.g., public land, fresh air). Maximization
of individual utility can lead to overuse and destruction (a tragedy) of the commons,
particularly when commons usage is not priced.
|
|
The repetitive trip between a traveler's home and work location, typically by
the same mode and at the same time of day, and usually on the same route.
|
|
The EPA's spreadsheet-based assessment model that estimates
changes in travel and emissions associated with transportation
control measures for commuting. The travel impacts component uses
pivot point analysis; the emissions component is based on
the MOBILE model
[ web ].
|
|
A model structure where one model variable can compensate for a change in value
of another variable. In choice situations, an individual can tradeoff a variable
(such as travel time) for another variable (such as cost), in selecting an
alternative from a choice set.
|
|
Policies and plans defining roadways to safely accommodate all users,
including motorized and non-motorized vehicles as well as pedestrians
[ web ].
|
|
In hierarchical modeling, a composite alternative represents the specific
alternatives for a defined level of choice. For example, several specific public
transit mode choices may be represented by a composite "public transit" alternative,
measured by the corresponding inclusive value.
|
|
In hierarchical modeling, composite cost is a weighted combination of the costs
of choice alternatives for a defined level, the correct specification being a
logsum formulation.
In conventional travel forecasting, feedback
to trip distribution might utilize composite costs that reflect
all relevant modes of travel.
|
|
The long-range plan for a community's future development, a comprehensive
plan (also known as a general plan or a master
plan) defines goals and objectives, policies and standards, and constraints
for the growth and development of the community. The plan provides a
land use and zoning plan indicating
planned land uses (e.g., residential, commercial, institutional) for districts
and parcels, and addresses all planning elements including
transportation infrastructure and services, the natural and built environment,
and demographic trends.
|
|
A measure of algorithm scalability defined by problem class, providing an
upper-bound impact on memory and run-time as problem size increases. O(•),
or "Order of" notation, describes the upper bound for the
magnitude of a problem's computational complexity.
|
|
In computational complexity theory:
[1] P, or Polynomial class, are decision problems that can be
solved in polynomial time on a deterministic Turing Machine (each state has
a single rule to follow)
[2] NP, or Non-deterministic Polynomial, are decision
problems that can be solved in polynomial time on a non-deterministic Turing
Machine (each state has multiple rules)
|
|
A term used synonymously with density in
traffic flow as a measurement of vehicles per mile.
|
|
A descriptive model of urban development developed by Burgess (1924) depicting
urban form as a series of concentric rings extending
from a central business district and defined by different
land uses and socio-economic
characteristics. Compare with the Sector Model and the
Multiple Nuclei Model.
|
|
See Concentric Ring Model.
|
|
A statistical measure to quantify uncertainty by bracketing a sample estimate
by a range of values within which the estimate is expected to occur for a
specified level of significance. Such assessments typically are not incorporated
into any estimates made in transportation planning and modeling.
|
|
A Clean Air Act requirement that regional transportation
plans must be in agreement with commitments designed to meet
federal air quality standards to receive federal
approval and funding. Planned transportation projects must not worsen an
area's air quality goals as established in the State Implementation Plan
(SIP).
|
|
Interference between vehicles as flow densities increase, causing reduced speed
and increased travel time. At low volumes, limited interaction allows vehicles
to proceed uninterrupted and flow is uncongested. As volume approaches capacity,
vehicle interaction increases and queues begin to form (see also
recurrent and non-recurrent congestion).
|
|
The economic value of travel time delay based on
value of time and excess fuel consumption, usually
averaged and presented for major metropolitan areas
(see TTI's Urban Mobility Report).
|
|
Required by California's Proposition 111 (1990) in metropolitan counties to link
land use, transportation, and air quality for growth management that effectively
utilizes transportation funds, alleviates traffic congestion, and improve air
quality and other congestion impacts (see CMA [2]).
|
|
Transportation facility use fees that vary with the level of congestion or,
by proxy, by time of day, and designed to optimize the performance efficiency
of the facility (also known as the value pricing).
|
|
A class of link performance functions (LPFs) developed by
Speiss that are similar to, but address some theoretical limitations of, the
BPR LPF. Conical LPFs can be geometrically interpreted
as hyperbolic conical sections.
|
|
The evolution of transportation systems from infrastructure connectivity toward the
integrated connectivity of travelers, vehicles, and infrastructure, communicating
via integrated active and passive data streams. See Vehicle Infrastructure Integration
( VII ) and Intelligent Infrastructure.
|
|
A general network term for measures that define the degree
that nodes are connected via paths.
Perhaps most applicable to transit systems where paths can be defined as
transit lines and connectivity can be defined in
terms of the number of transfers required to reach a particular destination
(not reachable or reachable with 0, 1, 2, etc. transfers), computable by
powering an adjacency matrix of transit lines.
|
|
A network property equivalent to Kirchhoff's 1st Law
constraining the flow into a node to be equal to the
flow out, corresponding to standard nodes (such as intersections).
|
|
An estimator is consistent if it converges to the population parameter
as the sample size increases.
|
|
A restriction limiting a system's behavior and thus imposed on appropriate
variables in the associated model.
|
|
Hagerstrand defined authority constraints as limitations
on travel and activity performance imposed by institutional factors, such as
lack of a driver's license due to age.
|
|
Hagerstrand defined capability constraints as limitations
on travel and activity performance imposed by physical factors, such as inability
to be at two places at the same time.
|
|
Hagerstrand defined coupling constraints as limitations
on travel and activity performance imposed by requirements to travel or
perform activities with another person or the requirement for a drop-off
activity to preceed the subsequent pick-up activity.
|
|
Hagerstrand's model of time geography
included authority, capability,
and coupling constraints.
|
|
A statistical index that measures the change in the cost of living, reflecting
prices of consumer products, transportation, housing, and other goods and services.
It is a an indicator of the general level of prices, and thus of inflation, and is
used to adjust income and costs in forecasting model applications.
|
|
The difference between what decision-makers would be willing to pay and what they
actually pay at a given equilibrium volume. Geometrically, it is the area under
the demand curve and above the equilibrium cost.
|
|
The standard shipping unit that facilitates freight tranportation
over multiple modes and through multiple transfer facilities (e.g., between
containerships, railcars, and trucks) throughout the supply chain.
|
|
A collaborative, interdisciplinary planning and design approach in which
stakeholders are integral parts of the design process
and objectives such as safety, mobility, environmental
sustainability, and preservation of community values
are simultaneously addressed.
|
|
A discrete model of the relationship between two or more categorical variables,
tabulating the joint distribution and with row and column sums providing the
marginal distributions. Model statostical significance can be assessed with a
chi-squared test. Non-categorical variables can be used by defining categories
a priori.
Category Analysis is similar to a contingency table except,
in place of a joint frequency in each cell, the corresponding average value of
a third variable is presented (e.g., average trip rates corresponding to the
value of the explanatory variables).
|
|
Dynamic traffic modelling software for modeling networks with time varying
traffic flows. Developed by TRL [ web ].
|
|
In a before-after study, a sample with characteristics
similar to the implementation site but which do not include the infrastructure
or service improvements, but would be subject to similar external factors in
these assessment of ex post performance.
|
|
The operations management components of a transportation system,
including traffic signals, signs, controllers, detectors,
and other hardware/software.
|
|
In iterative models, achieving a defined tolerance of approaching a known value
or reducing a defined gap.
|
|
In iterative trip assignment, a weighted combination of the
current solution Va(n-1) and a linear approximation
Fa(n), or:
Va(n)=(1-αn)Va(n-1) + αn Fa(n)
(see Frank-Wolfe or MSA[2]).
|
|
In traffic engineering, the linking of timing patterns at
a sequence of intersections to facilitate the progression
of through traffic.
|
|
An abstract line defining the external boundary of a study area.
Internal cordon lines are sometimes used as screenlines to compare
estimated and observed flows into and out of a sub-area (such as a
CBD).
|
|
A standardized measure of the strength of a linear relationship between two variables
(-1 ≤ correlation ≤ +1).
Correlation does not imply any causal effect.
|
|
A linear study area along one or more transportation
facilities for which estimates of travel demand and system performance are desired.
|
|
Created by California's Proposition 1B in 2006, the CMIA
provides funds for the California Transportation Commission
to allocate for performance improvements to the state highway system to relieve
congestion, enhance mobility, and improve safety.
|
|
A corridor planning and management process required by
California's Proposition 1B for the management of all
modal infrastructure and services in a corridor to optimize the efficiency and
effectiveness of transporting people and goods. CSMPs integrate transportation
systems planning with systems management
[ web ].
|
|
A comprehensive traffic microsimulation software package, part
of TSIS (Traffic Software Integrated System). Developed by FHWA
[ web ].
Other traffic microsimulation packages include AIMSUN,
Cube Dynasim, Paramics,
SimTraffic, TransModeler,
and VISSIM.
|
|
A price paid or otherwise associated with a transaction. Costs
represent trade-offs between alternate uses of resources, and can be
measured by money and time expended, or opportunities lost, to obtain a
benefit. Transportation costs directly incurred
include travel time costs; out-of-pocket costs (fares, tolls, and parking
charges); and vehicle expenses (capital and operating costs). Transportation
costs indirectly incurred include infrastructure capital, maintenance, and
operations costs; accident costs; and environmental costs. Transportation
benefits are equivalent to a reduction in costs (such as reduced travel time).
|
|
See Benefit-Cost Analysis.
|
|
A measure of input per unit of output, such as input cost per unit of an
output performance measure (e.g., cost per passenger-mile
traveled). Often used in comparing alternatives when output performance measures
cannot be expressed in monetary terms, selecting the alternative that has the
greatest effectiveness for a given input cost.
|
|
A regional agency serving multiple jurisdictions (including
counties and cities) to address specified regional issues such as transportation
planning.
|
|
The number of activations of an inductive loop detector in
a specified counting interval (usually 30 seconds) that
is converted to a volume estimate (compare to
presence and occupancy).
|
|
A defined period of time during which measurements are made (e.g., 30 seconds
for an inductive loop detector or 24 hours for a trip survey).
|
|
See Consumer Price Index.
|
|
A quantitative standard by which achievement of objectives
can be measured.
|
|
The 1970 Clean Air Act identified six criteria pollutants,
including ozone (O3), carbon monoxide (CO),
nitrogen oxides (NOx), sulfur oxides (SOx),
particulate matter (PM10), and lead. The EPA
establishes the associated standards (see NAAQS).
|
|
A tabular classification of two or more categorized variables.
See Category Analysis.
|
|
An elasticity defined as the change in market share of an
alternative due to a change in an attribute of a competing alternative (e.g., the
change in transit demand due to auto fuel price increase). Also called an indirect
elasticity. Compare with direct elasticity.
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A survey of and data from a sample of observations collected at
a single point in time. Compare with longitudinal surveys and data.
|
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The cross-sectional design of full roadway right-of-way, including the roadway
itself, median and shoulders, sidewalks and bike lanes, drainage and side slopes,
and other components, and reflecting topography, safety, facility type, speed,
and other design concerns (see geometric design as well as
vertical and horizontal alignment).
|
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Context Sensitive Design (see CSD).
CSS is a Context Sensitive Solution.
|
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California Statewide Freight Forecasting Model
(see CSFFM ).
|
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A Corridor System Management Plan
(see CSMP).
|
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California Statewide Travel Demand Model
(see CSTDM ).
|
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See California Transportation Commission (CTC).
|
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Caltrans' Traffic Signal Management and Surveillance
System developed for statewide deployment to monitor and control traffic signals.
|
|
See California Transportation Plan (CTP).
|
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The Census Transportation Planning Package is created
from portions of the decennial US census to provide
information on basic travel characteristics and associated socio-economic
characteristics (for the ten percent sample)
[ web ]
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A software packages for travel forecasting, incorporating an integrated GIS.
Developed by Citilabs [ web ]. Other travel
forecasting packages include EMME/2, QRSII,
MinUTP, T-Model, Tranplan,
and TransCAD.
|
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The California Urban Futures Model
(see CUF).
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A control line for which estimated and observed performance measures are aggregated
and compared for model validation or for performance assessment, a cutline
is similar to a screenline but only partially splits a defined
sub-area (or corridor), thus capturing local flows that
cross through, but not flows bypassing, the sub-area. With definition of spatial
scale somewhat arbitrary, these terms are often used interchangeably
(see also cordon line).
|
CVO |
Commercial Vehicle Operations, an original component
of Intelligent Transportation Systems.
|
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A complete sequence of signal control indications.
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The total time for a traffic signal to complete a full sequence of signal
indications (i.e., a cycle)
and return to the initial indication.
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Previously a somewaht pejorative term for brute force analysis leading the generation
of research hypotheses, data mining has become a generic
term for a range of techniques used to seek new relationships, patterns, and hypotheses
within large databases.
|
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Davidson's Link Performance Function is based on queueing
theory and assumes that arrivals (demand) can not exceed the service rate
(capacity). Although theoretically sound, it is not amenable to standard
iterative assignment algorithms that are designed to not
restrict link flows to link capacity (thus, the BPR LPF
is often used). Akcelik provides a modified version that
resolves this issue.
|
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Segment of a transit route driven by a transit vehicle not in revenue service.
Similarly, an empty backhaul in freight transportation (usually trucking).
|
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A method of estimating position based on starting position, speed, and elapsed time.
|
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The historical approach approach to transportation decision-making in which
planners made decisions, then called public meetings to announce and defend
those decisions to the public, without allowing time for integrated public
involvement in the transportation planning process.
|
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Information technology and software that utilize decision models,
expert knowledge, rule-based systems, and other methodologies
for unstructured problem solving and decision-making in an interactive environment.
|
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An hierarchical mapping of sequential decision-making where a choice of any
branch of the tree leads to further decision points (and usually eliminates
choice on prior branches).
|
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A short- to medium range wireless communications protocol designed for
ITS applications such as vehicle to infrastructure integration
(VII), including V2V (vehicle-to-vehicle) and V2R
(vehicle-to-roadside) technologies, operating in the 5.9 GHz frequency band
(also used by Wi-Fi).
|
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Each of N sampled data points is free to take on any value. When a parameter is
estimated for this data, this freedom to vary is restricted. The precision of an
estimate is a function of degrees of freedom |
|
See EIR/EIS.
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The difference between the actual travel time on a link and the free-flow
travel time. Often represented as total or average delay (taken over all
vehicles in a defined period) and serving as a measure of congestion. Delay
may be attributed to queueing based on congested flows
and/or signal timing.
|
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A planning, prediction, or decision-making tool in which a panel of experts,
via interations of individual assessment and feedback to the panel, reach a
consensus, often when input data and decision criteria are subjective rather
than objective.
|
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The quantity of transportation desired at a given price, typically defined
for specific users in a specific time and place.
|
|
Travel demand analysis encompasses (a) forecasting future volumes and level of
service for planned transportation facilities and services, (b) evaluating the
associated benefits and costs, and (c) developing plans for system operations.
|
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In Transportation Systems Analysis, a demand function
reflects characteristics of the Activity System that
together with performance functions (which reflect
characteristics of the Transportation System) determine
network flows (volumes and travel times).
A demand function relates volume to a function of characteristics of
a given region and the associated level-of-service, or:
volume = D( Asys, LOS )
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A form of paratransit that features reservation-based
and/or on-demand, door-to-door transportation within a defined service area,
operated by transit agencies, community groups, or private operators, and
providing high quality transit service to primarily elderly and disabled riders.
|
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Characteristics of the population, including population and household counts
as well as descriptors such as age and gender, usually defined at the
zonal level. While often used interchangeably with the term
socio-economic data, demographic data are best viewed as fixed
population characteristics that define a state (such as age and gender) whereas
socio-economic data correspond to time-varying attributes that define status within
a state (such as auto ownership and income). Demographic and socio-economic data,
together with land use data, are key inputs to
trip generation.
|
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The field of research and analysis on the size, structure, and distribution
of population, including the dynamics of fertility,
mortality, and migration, as well as related issues such as housing and
socio-economic characteristics.
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[1] The number of flow units (vehicles) present on a defined
section of roadway at a given time (typically measured in vehicles per mile).
With volume and speed, density defines
the fundamental diagram of traffic flow (which provides a
direct link to performance functions).
[2] The number of units of some activity measure (population, employment, etc.)
per unit area (e.g., population per square mile).
[3] In the 3D process, density, design,
and diversity are measures to comparatively describe the
built environment (in 3D, an area's density is defined as the sum of population
and employment divided by total land area).
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The change in density of population (or other
demographic or socio-economic variable)
over distance from a defined spatial center (such as a CBD).
In the standard monocentric land use model, the density
gradient is theorized as a negative exponential distribution.
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Federal or state Department of Transportation
(see DOT).
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The clock time that a trip begins. Departure time has historically been
addressed in aggregate terms with trips assigned to the period in which it was
assumed to start and end based on time in motion studies
associated with travel surveys. Departure time is
more explicitly addressed in activity-based microsimulation
models.
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A variable whose value depends on that of other (explanatory,
or independent) variables.
|
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The demand for travel is derived from the demand to perform an
activity that is located so as to require travel to access the activity.
|
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[1] Design is a systematic process to develop solutions to address a specified
problem or need. Design reflects an open-ended problem-solving approach that
recognizes alternate solutions and relevant constraints.
[2] Design also refers to the resulting solution itself, in general or specific
terms.
[3] Together with density and diversity,
design forms the 3 Ds, measures to comparatively describe the
built environment. In the 3D process, an area's design is a weighted combination
of sidewalk completeness, route directness, and street network density.
|
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A project delivery process where a single party is contracted for both project
design and construction. In the conventional process, a construction contract
would follow completion of a separate contract for project design.
|
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The thirtieth highest hourly traffic volume (in vehicles per hour) for the
design year.
|
|
A graphical representation of the overall demand for travel between two points,
typically drawn as a straight line from an origin to a destination with line
width scaled to overall demand and often color-coded by trip purpose, mode, or
other relevant attribute.
|
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The location or zone where a trip ends, but also used for
the trip itself: a zone is a destination for N trip destinations.
The origin is where a trip begins.
Compare with production and attraction.
|
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Destination Accessibility is a measure of a zone's or an area's regional
accessibility. Together with density,
design, and diversity, destination accessibility
forms the 4 Ds, measures to comparatively describe the built
environment. An extension of the 3D process, destination is an
index defined for a given area i as the denominator of a gravity model for
a region, or Σj Aj f(cij), where
Aj is the number of attractions in zone j and f(cij) is
some function of the generalized cost from area i to destination j.
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The process by which a trip maker located at a specific origin seeks a location
at which to perform an activity for a specific purpose. Most conventional models
address destination choice via a deterministic trip distribution
function, such as a gravity model, rather than an explicit
choice model such as Logit.
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A device for identifying the presence or passing of a vehicle at a particular
location, often used interchangeably with sensor (see
inductive loop detector). A loop is a passive detector,
whereas a pedestrian push button for a walk signal is an active detector.
|
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A detector for counting the number of vehicle activations
at a particular location over a defined period (e.g., 30 seconds for most
freeway lane detectors -- such freeway detectors often also compute and convey
occupancy data).
|
|
A detector located upstream from an intersection to identify
vehicles on an approach to extend the current green time by a fixed or decreasing
amount until a phase maximum is reached.
|
|
A detector for identifying only the
presence of a vehicle at a particular location,
sending a binary signal to the controller to address the corresponding
movement according to the current control logic. Most common deployment
is at intersection stoplines.
|
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Same as impedance.
|
|
Not a probabilistic function or process (see stochastic).
|
|
A network loading process that assumes travelers have perfect knowledge of all
path travel times and thus choose paths in a deterministic
fashion (e.g., Wardrop's Principles; see also
iterative assignment).
Compare to Stochastic Assignment.
|
|
Design Hour Volume (see DHV).
|
|
A stochastic trip assignment algorithm that obviates path
enumeration. Equivalent to a logit path assignment,
Dial's follows a 2-pass algorithm to assign flows to
"reasonable" paths (a path is reasonable if it moves further from the origin
and closer to the destination). In the forward pass, link weights are computed
based on link likelihoods, proceeding from the origin; in the backward pass,
link volumes are computed based on weights, proceeding from the destination.
A 1-pass algorithm uses a relaxed definition of "reasonableness".
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A commonly used expression for a carpool lane, based on
the controversial Santa Monica, CA experiment where an existing freeway lane
was converted to exclusive use by HOVs and demarcated with
painted diamonds on the pavement. Such delineation may also be used for lanes
dedicted to other modes, such as bike lanes.
|
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A method to improve the accuracy of GPS measurements by
referencing a known fixed location to compare errors from GPS satellites.
|
|
The most efficient algorithm to find the minimum path tree from a given origin
on a transportation network based on the iterative scanning of links outbound
from a node on the tree. Alternate algorithms (e.g., Moore's)
differ primarily in the sequence that nodes are evaluated for inclusion on the
minimum path. At each iteration, Dijkstra's selects the node
closest to the origin (and is thus a label-setting path
algorithm).
|
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An aggregate demand model that represents multiple travel choices in a single
equation. The inherent complexity is controlled by restricting the application
to well-defined travel corridors.
|
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An elasticity defined as the change in market share of an
alternative due to a change in an attribute of that alternative (e.g., the change
in transit demand due to a transit fare increase).
Compare with indirect elasticity.
|
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The proportional distribution of total traffic volume on a two-way facility.
|
|
A model with units of analysis defined as the actual behavior units. In travel
forecasting, the behavioral unit is the individual decision-maker or the
household (see Aggregate Model).
|
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Commonly used synonymously with interest rate, a measure of the time
value of money used in "discounting" future costs and benefits to equivalent
present day values (technically, for interest rate i, the discount rate d =
[i/(1+i)]).
|
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A modeling approach, also known as qualitative choice
models, representing a decision-maker's choice among a finite set of distinct
choice alternatives (such as the choice of alternate modes among car, bus, or
walk).
|
|
A mathematical model that estimates the atmospheric distribution of pollutants as a
function of emissions rates, source location, and other factors.
|
|
The basic measure of spatial separation and thus a measure of total travel.
Defined alternatively as straight-line distance ("as the crow flies") or as
actual travel distance from a trip origin to its destination. In policy studies,
distance is often replaced by policy-sensitive equivalents such as travel cost,
travel time, or generalized cost
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An area's distance from a heavy rail transit station is a measure of an area's
ability to draw trips from street networks. Together with density,
design, diversity, and destination
accessibility, distance forms the 5 Ds, measures to comparatively
describe the built environment. An extension of the 4D process,
the distance measure, defined as an exponential function of population and employment
within a half mile of a rail station, rail service frequency, and feeder bus service
frequency), is only applicable in zones containing a heavy rail station.
|
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A state where non-driving activities divert a driver's attention from the primary
task of controlling the vehicle in a safe manner, including phone/text use, using
auxiliary in-vehicle systems such as radios or navigations systems, and attending
to other personal demands or demands of other vehicle occupants. Distracted driving
may contribute to as many as ten percent of all traffic fatalities each year.
|
|
Generic term for trip distribution.
|
|
Aggregations of TAZs to facilitate model development or
display of model results. Trip attraction models often
are estimated for districts since residential-based travel surveys do not
usually provide enough observed attractions in each TAZ to estimate the
zonal attraction model directly.
|
|
Utility that is negatively valued is often referred
to as disutility (e.g., travel time or cost).
|
|
Vehicular emissions that occur on a daily cycle and that are not necessarily
related to vehicle use. For example, emissions from a vehicle's fuel tank that
occur even when a vehicle is not running.
|
|
Utilized in early mode and route choice
studies, diversion curves expressed the proportion of trips that would
use a particular mode (e.g., car versus bus) or route alternative (e.g.,
freeway versus arterial) given relative travel costs of the alternatives.
|
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Diversity is a measure of an area's land use mix, or more specifically, its
jobs-population balance. Together with density
and design, diversity forms the 3 Ds, measures
to comparatively describe the built environment. In the 3D process, an area's
diversity is defined as {1 - [ abs( (E/P)p - e ) / ( (E/P)p + e) ] }, where E and P
are regional employment and population and e and p are the corresponding local values.
|
|
A somewhat misleading name for the No Build Alternative.
"Do Nothing" means no actions other than those which have already been
planned and programmed.
|
|
A pier is a port facility for loading/unloading ships that extends perpendicular
from the shore; a wharf differs only in that it is built parallel to the shore.
A dock is the space in which a ship moors alongside a pier or wharf (a dry dock
is this space with the water removed for ship building or repairs).
Otis Redding was sitting on a pier or a wharf.
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A federal or state Department Of Transportation. The federal
USDOT includes FHWA, FTA,
and other transport agencies [ web ].
Each state has an equivalent agency, in most cases also named a DOT
(e.g., Caltrans)
|
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A gravity model used for trip distribution
derived via the Most Probable Distribution (Maximum Entropy)
approach where both trip productions and attractions are constrained to match those
input from trip generation (see Singly Constrained Gravity Model).
|
|
Traffic or infrastructure that is located ahead of the current position in
the direction of movement (as opposed to upstream traffic
or infrastructure that may be seen looking back over your shoulder).
|
|
Direct Residential Allocation Model and
EMPloyment ALlocation model are components of the Integrated
Transportation Land Use Package, ITLUP.
|
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Dedicated Short Range Communications
(see DSRC).
|
|
Decision Support Systems (see DSS).
|
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Dynamic Traffic Assignment (see DTA).
|
|
The Direct Travel Impact Model is a grid-based
vehicle emissions forecasting model developed by Caltrans,
combining EMFAC emission rates with network assignment
output, increasing emission resolution by using trips defined by TAZ rather
than VMT.
|
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In linear programming, the dual is complementary to
the original (primal) problem. The minimization of a primal LP with n decision
variables and m "≥" constraints is equivalent to the maximization of a
dual LP with m dual variables and n "≤"
constraints.
|
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In the dual mathematical program, each primal constraint is
represented by a dual variable, a shadow price
that represents the marginal change in the optimal value of the objective
function for a unit change in a constraint (equivalent to the value of the
Lagrange multiplier at the optimum).
|
|
Deterministic User Equilibrium (see UE).
|
|
Processes and technologies that existed before the advent of "smart" or
"intelligent" transportation systems introduced in the early 1990s (see
humor).
|
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An abstraction of a real-world attribute to facilitate model analysis:
[1] dummy variable: a means of accommodating non-metric variables in a
regression analysis via a binary variable indicating the
presence or absence of a particular value of the original variable;
[2] dummy (supply or demand) node: in the
transportation algorithm, total supply must equal
total demand; a dummy demand node is added is supply exceeds demand,
or a dummy supply node is added if demand exceeds supply.
|
|
Type of housing unit (e.g., single family detached, apartment, mobile home).
Has often been used in trip generation models due to high
correlations with household trip rates
and ability to directly observe. Same as Housing Unit.
|
|
Event-based, equilibrium dynamic traffic assignment
software developed by Inro [ web ].
|
|
In GIS, a process that allows attributes to be assigned to portions
of a line (e.g., a network link) without physically modifying line geometry.
|
|
Network assignment with dynamic (versus fixed) demand. DTA extends conventional
static trip assignment by integrating
the travel demand and traffic flow components.
|
|
DynaMIT is real-time software for ATMS and
ATIS support within a Traffic Management Center
(TMC). Developed by MIT
[web ].
|
|
Cube-Dynasim is real-time software system for simulating, visualizing, and
evaluating the effects of transportation and activity system changes. Developed
by Citilabs and linked with Cube travel forecasting software
[web ]. Other traffic microsimulation
packages include AIMSUN, CORSIM,
Paramics, SimTraffic,
TransModeler, and VISSIM.
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|
[1] DYNASMART (1994) is a mesoscopic simulation model for
dynamic network traffic analysis, featuring macroscopic
updating with individual (microscopic) vehicle tracking.
[2] DYNASMART-P is an intelligent transportation network design, planning,
evaluation, and simulation tool, initially developed at the University of Texas.
[3] DYNASMART-X is a real-time traffic estimation and prediction tool for
dynamic traffic assignment (DTA), developed at the University
of Maryland [ web ].
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An appropriation of public funds to a specific program or project, placed
in legislation by an elected official (AKA "pork").
|
|
The problem of inferring individual characteristics from population data,
such as inferring individual household characteristics based on TAZ data.
|
|
The application of statistical methods to the estimation of economic models.
|
|
A fundamental technique for describing and forecasting economic activity,
economic base sectors an economy (often measured by employment)
into basic (export-oriented) and one or more non-basic
(local-oriented, or service) employment sectors. The basic
sector fuels the local economy, driving service employment and population growth.
Local multipliers define functional relationships between
basic employment, service employment, and population.
The location quotient and minimum requirements
sectoring methods can be used to estimate basic employment by economic sector.
|
|
In comparing changes in average cost with increasing output, economies of scale
exist if average cost decreases with increased output (also known as increasing
returns to scale).
|
|
Cities of a recent vintage developed at the periphery of established metropolitan
areas (a named popularized in Garreau's (1991) Edge City).
|
|
Edie (1961) proposed the first two-regime traffic stream model
combining Underwood's model, which performed well for free-flow
conditions, and Greenberg's model, which performed well for
congested flow. Two-regime models have a discontinuity between regimes, often near
capacity.
|
|
A general system performance measure defined as the degree to which stated
goals and objectives are achieved (see also efficiency).
|
|
A general system performance measure defined as the ratio of system output
to system input, where system input is often cost
(see also effectiveness).
|
|
An estimator is efficient if it has a small sampling error.
|
|
Environmental Impact Report/Environmental
Impact Statement (see EIR/EIS).
|
|
See variable demand.
|
|
The elasticity of y with respect to x is the percent change in y with
respect to the percent change in x, or ey|x = (dy/y)/(dx/x). An
elasticity may be estimated at a point directly from a known function
(point elasticity) or may be estimated from two observations of x and y (arc
elasticity). Elasticity-based demand models provide estimates
of the sensitivity of demand to small changes in the model's explanatory
variables (see fare elasticity).
|
|
Electronic systems that collect vehicle tolls without requiring vehicles
equiped with a transponder to stop.
|
|
A non-compensatory choice model developed by Tversky (1972)
based on the elimination of alternatives from an individual's choice set for not
meeting a threshold on the highest ranked attribute (most important aspect), then
proceeding through lower ranked (less important) attributes until a single choice
alternative remains.
|
|
California's software package for calculating regional motor vehicle emissions.
EMFAC2014 is the current version (see also MOBILE,
MOVES)
[ web ].
|
|
A government's right to take private property for a public use, compensating the
property owner at market rates.
|
|
In transportation, the gases and particles discharged into the atmosphere
as byproducts of the combustion process of converting fuel to motive power.
These mobile source pollutants are primary contributors
to air quality problems in metropolitan areas.
|
|
An estimate of total atmospheric pollutants from mobile,
stationary, area-wide, and
natural sources for a specified period of time.
|
|
A software package for travel forecasting and transportation network analysis.
Developed by INRO [ web ].
Other travel forecasting packages include Cube,
QRSII, MinUTP, T-Model,
Tranplan, and TransCAD.
|
|
EMPloyment ALlocation model, a component of the Integrated
Transportation Land Use Package, ITLUP.
|
|
An first generation, recursive, simultaneous equation, sub-regional land use
allocation model developed by Hill (1965) for the Boston Regional Planning Project.
|
|
Based on actual experience rather than theoretical expectation.
|
|
The number of persons hired to work in a zone, region, or other defined
spatial unit, usually categorized by occupation or industry. An endogenous,
economic variable in land use models and an exogenous
explanatory variable in travel forecasting models,
especially trip generation where employment
variables (total, retail, or other categories) are critical in most
trip attraction models. Note that employment is
defined by work location while labor force is defined by
residential location.
|
|
A variable whose value is determined as an output from a mathematical model
(compare with exogenous ).
|
|
Transportation is movement, movement requires energy, and the transportation
sector of the economy constitutes a significant portion of total domestic
energy consumption, including about two thirds of domestic oil consumption.
Critical energy concerns include domestic dependence on foreign oil supplies
and the environmental impact of oil use in transportation.
|
|
The statistical basis for a family of aggregate trip distribution
models developed by Wilson (1967), including growth factor,
gravity, and intervening opportunity models.
The derivation is based on the most probable distribution of a
trip matrix found by maximizing an entropy function subject to constraints on
productions, attractions, and travel cost.
|
|
[1] The natural environment encompasses all biological and physical
components of the earth or a defined region.
[2] The built environment is the man-made infrastructure serving
human activity.
|
|
A NEPA-required process and report that identifies
the environmental impacts of project alternatives, leading to either a
Finding of No Significant Impact (FONSI) or
an Environmental Impact Study (EIS).
|
|
An Environmental Impact Report documents the comprehensive
analysis of the environmental impacts of proposed transportation and land
development projects, as required under CEQA. The parallel
federal requirement is an Environmental Impact Statement,
a report required under NEPA.
Draft EIR/EIS are circulated for agency and public comment. The final EIR/EIS
must address significant impacts and also provide means to
mitigate adverse impacts.
|
|
An Environmental Impact Study is a comprehensive analysis of
the environmental impacts of proposed transportation and land development projects.
An Environmental Impact Statement (EIS) is the federal report
under NEPA requirements;
an Environmental Impact Report (EIR) is the
California report under CEQA requirements.
Draft EIR/EIS are circulated for agency and public comment. The final EIR/EIS
must address significant impacts and also provide means to
mitigate adverse impacts.
|
|
In transportation, the process of having planning, programs, and policies that
reflect meaningful participation of all impacted parties and the provision of
facilities and services that reflect an equitable distribution of environmental
costs and benefits.
|
|
The United States Environmental Protection Agency,
responsible for administering Federal environmental laws, including the
Clean Air Act.
|
|
A system state where overall demand and system
performance are balanced. Any increase in demand corresponds
to an increase in cost that reduces that demand. Network flow is in equilibrium
when no traveler can unilaterally change route and be better off, thus there is
no incentive to change.
|
|
A trip assignment algorithm that solves for an
equilibrium solution for network flows.
Deterministic user equilibrium assumes that paths are chosen
based on actual link costs; stochastic user equilibrium
assumes that paths are chosen based on perceived link costs.
|
|
A normative measure of fairness among transportation system users and non-users
relative to costs and benefits.
|
|
In project appraisal, the discounting
of all current and future benefits and costs, over a defined project lifetime,
to an equivalent annual value.
|
|
Equivalent Single Axle Load (see ESAL).
|
|
Estimation, part of the model specification process,
is the formal computation of the parameters for an hypothesized model, to maximize
the likelihood of fitting observed data. In comprehensive model systems such as the
Four Step Model, individual models are independently estimated.
The model system as a whole is validated prior to any policy
application.
Note: In travel forecasting, the terms estimation
and calibration often have been used interchangeably.
Determining the structure of the model is explicitly part of the estimation
process thus lending it greater statistical formality, but both terms reflect the
same overall objective. If the structure of the model is pre-determined, then
perhaps calibration is the better term. If model specification is involved, then
perhaps estimation is the better term.
|
|
An estimated or calibrated value for an unknown population
parameter.
|
|
Electronic Toll Collection, the collection of roadway
tolls based on automated vehicle identification (AVI).
|
|
A carbon-based, alternative fuel that is an alcohol fermented from corn
or other bio-sources.
|
|
A landmark in zoning law was the United States Supreme Court's 1926 decision
(Village of Euclid, Ohio vs. Ambler Realty Co) that supported the legal authority
of local governments to control public and private land, including such building
requirements as use category, size, height, parking, and setbacks via
zoning ordinances.
|
|
As part of the Transportation Planning Process, evaluation
is the process of systematically assessing the costs and benefits of competing
alternatives. In addition to such a priori applications, evaluation is
also performed in ex post performance assessment
of existing transportation systems.
|
|
Proposed by Evans (1976) to find the equilibrium solution of a combined model
of trip distribution and trip assignment,
formulated as a constrained optimization problem.
|
|
Any accident, incident, or planned occurance that affects transportation
system performance. A primary role of Transportation
Management Centers is to expeditiously resolve events.
|
|
A broad family of algorithms for search and optimization first
introduced by Fogel (1966) that include genetic algorithms but
in general are not dependent on a defined fitness function but are more dependent
on diversity and mutation and thus less likely to be caught in local optima.
|
|
A variable whose value is determined independently and is used as an
input to a mathematical model (compare with endogenous ).
|
|
In travel surveys, the parameter that converts sample data to population-level
equivalents, based on the designed sampling frame.
|
|
A software system that incorporates quantitative and qualitative professional
expertise and judgment in a knowledge base integrated with an inference
engine to emulate the decision process of experts in a particular area
( also know as Knowledge-based System ).
|
|
An exogenous variable hypothesized to influence the value of a
dependent variable.
|
|
The assumption of unconstrained natural increase of a population yields the
exponential growth model (Malthus, 1798) where the growth rate is
directly proportional to the current population (the discrete equlivalent is
the geometric growth model). Compare with the logistic
growth model.
|
|
A "door" on the cordon line of a study area
corresponding to major entry and exit points for external trips
through, into, and out of the study area.
|
|
While a Household Travel Survey collects data on travel
behavior for residents of a study area, an external
survey collects travel data on non-residents who travel to,
from, and through the study area. These trips are identified as internal/external
(IE or EI) or external/external (EE, or thru trips). Usually conducted every 10
years at key external stations.
|
|
A trip with either its origin or its
destination located outside of the study area.
The external trip end is assigned to an external station. Often
referred to as "IE" for internal-to-external or "EI" for external-to-internal trips.
A through trip has both trip ends outside the study area (often
referred to as "EE" or for external-external). An internal trip
has both trip ends inside the study area (often referred to as "II" for
internal-internal).
|
|
An economic cost or benefit that is experienced by individuals not directly
involved in an activity and thus not reflected in the price of the activity
(e.g., air pollution).
|
|
The process of forecasting values of a dependent variable
beyond the range of observed explanatory variables, usually by estimating a
model (for example, a trend projection or other
time series model) and applying it beyond the observed
range of the explanatory variables, thus increasing uncertainty in the
estimated values.
|
|
Outlying rural communities beyond traditional suburbs
and characterized by significant commuting flows with the core urban area
(see metropolitan classification).
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| F | [ back to top ] |
|
|
See Friction Factor.
|
|
A test of model significance in least squares estimation,
an F statistic is computed in an Analysis of Variance as
the ratio of the mean sum of squares accounted for by the model to the residual
mean sum of squares. If the calculated value is greater than the critical
value, then the null hypothesis that all model
coefficients are equal to zero is rejected (see t Test).
|
|
A component of transportation infrastructure, often taken as an operational
facility such as a roadway or guideway, but may also including terminals.
In general, any building or other dedicated infrastructure.
|
|
A branch of operations research that develops and applies
methods and models for the spatial location of facilities with respect to
transportation and activity systems.
|
|
Describes the operational design of a roadway based on access control, speed
limits, and topography. Functional classifications include
freeways, arterials, and local streets. In travel forecasting,
facility type and area type are used to create a
look-up table that provides default link
speeds and capacities.
|
|
Freight Analysis Framework (see FAF)
[ web ].
|
|
A national freight data survey and data base documenting
flows by commodity (see also Cal-Fred )
[ web ].
|
|
Federal-Aid Highway Act (see FAHA).
|
|
Fast And Intertwined Regular lanes is a pricing
concept that (physically) divides free, general-purpose traffic lanes into
"fast" toll lanes and "regular" untolled lanes, each electronically monitored.
Drivers in regular lanes would receive credits toward use of the fast lanes
to compensate for loss of access to the converted lanes and the associated
delay increase in the remaining regular lanes. It is claimed that
FAIR lanes can increase freeway throughput, speed public transit
service, let drivers bypass congestion, and cure gum disease.
Any semblance to diamond lanes is likely inadvertent
[ web ].
|
|
In zoning, the Floor Area Ratio
expresses the total floor space of a building as a fraction of the total area
of a site. FAR combines horizontal (e.g., setback) and vertical (e.g.,
height restriction) dimensional limits into a single parameter that correlates
well with site traffic impact measures (trips, parking demands, etc.).
|
|
The price paid by a user to utilize a public
mode of transportation.
|
|
The elasticity of transit demand D with respect to transit
fare f, defined as the percent change in demand with respect
to the percent change in fare, or eD|f = (dD/D)/(df/f), has been found
to be about -0.30 in many studies. For small changes in
fare, a corresponding linear change in demand can be estimated.
|
|
The proportion of operating costs covered by passenger fare revenue.
|
|
The Fatality Analysis Reporting System
(see: FARS).
|
|
The Fixing America's Surface Transportation Act
(see: FAST).
|
|
FARS is the nationwide database of fatal injuries suffered in motor vehicle traffic crashes.
|
|
A solution that satisfies problem constraints but may not be optimal.
Many algorithms require an initial feasible solution
for execution.
|
|
The series of federal transportation authorization bills
signed into law over the past century, beginning with the Federal Aid Road Act of
1916 and commonly named Federal Aid Highway Acts from 1938 through 1987.
The last three acts have been more whimsically named ISTEA (1991),
TEA-21 (1998), and SAFETEA-LU (2005).
|
|
The generic name for the funding program between the federal government
and local and state agencies.
|
|
The National Highway System and the Dwight D. Eisenhower
National System of Interstate and Defense Highways.
|
|
Daily federal publication that publicizes regulations and legal notices
issued by various departments of the Federal government.
|
|
For vehicular emission models, emission factors are derived
from laboratory experiments measuring vehicle emissions with a dynamometer for
a standard Federal Test Procedure (FTP) driving cycle. The FTP was developed in
the 1970s to capture real-world driving characteristics using a defined cycle
of accelerations and decelerations.
|
|
Using the output from a step in a modeling sequence as revised input to a prior
step to re-execute the model sequence. In the last step of the Four
Step Model, trip assignment has conventionally been equilibrated given a fixed
trip table as input, with no feedback to prior steps. Most recent
models use assigned link volumes to revise link travel times and feed them back to
the minimum path algorithm to repeat trip distribution and mode choice with more
consistent estimates of network travel times and costs.
|
|
The Federal Highway Administration, part of
USDOT, administers federal-aid highway programs that
provide the states with funding and technical support for the design,
construction, and management of highway infrastructure.
|
|
First In First Out, a single-server queueing regime
where service is provided in order of arrival in the queue.
|
|
The common public transit problem of system access and egress:
how to get from home to the transit stop (the "first mile") and how to get from the
transit system to your final destination (the "last mile").
|
|
Costs that remain constant, independent of the level of
transportation operations (such as infrastructure costs). Also known as
capital costs. Compare to variable cost.
|
|
Public transportation service provided on a pre-defined route, with pre-defined
access and egress points, and usually on a pre-defined schedule,
typically associated with bus transit service but also applicable to other modes.
|
|
A traffic signal timing plan with a set sequence of
pre-determined phase lengths defined for a particular
period of operation. The resulting fixed cycle length
facilitates coordination, but there is no real-time
connection between actual vehicle demands and signal operations.
|
|
A pavement with a bituminous asphalt wearing surface and that is supported by
and distributes loads to the subgrade (see rigid pavement).
|
|
The Fixing America's Surface Transportation Act was
the federal transportation authorization enacted in 2016,
continuing the series of Federal Aid Highway Acts (FAST was
preceded by SAFETEA-LU.
[ web ].
|
|
A method of traffic data collection where a test vehicle drives with the
traffic stream at the ambient speed in each direction to estimate link
volume and speed. Floating cars
have evolved into probe vehicles to estimate traffic
stream charactistics with advanced location and communication technologies.
|
|
See FAR.
|
|
In Transportation Systems Analysis, the output of demand
performance equilibration (trip assignment in the basic
Four Step Model) is a set of flows, represented by a set of
link volume and level-of-service measures.
Flow is sometimes taken as only traffic volume (especially in traffic operations),
typically measured in vehicles per hour (vph).
|
|
An algorithm to find the minimum paths between all pairs of
network nodes based on the iterative evaluation of potential intermediate nodes.
Floyd's is a label-correcting path algorithm that operates
on all nodes in a network, not only on centroids, thus it is not recommended for
conventional transportation networks. See Dijkstra's and
Moore's.
|
|
A focus model uses an existing regional transportation model as a base, and
holds the activity system outside of the primary (or focused)
study area constant or aggregates these data into larger zones (particularly
as distance from the focus area increases). Within the focused area, the detail
associated with the activity and transport
systems is typically increased, allowing for a more detailed analysis and evaluation
of local demand and performance. See also sub-area extraction.
Compare with window model.
|
|
Finding Of No Significant Impact: a document
providing the justification for a planned action having no environmental impact
that would require the preparation of an EIR/EIS.
|
|
Forecasting (or prediction) is the application of a
calibrated or validated model
or model system to estimate future system performance. In conventional
travel forecasting, the process involves the sequential
application of the four step model for each defined
transportation system alternative, as a function of a
specified future activity system.
|
|
Oil, coal, natural gas, or other naturally-occurring but non-renewable
hydrocarbons fuels produced by the decomposition of
organic material over millions of years.
|
|
The conventional model for travel forecasting, so named for the four major steps
of the process: trip generation, trip distribution,
mode choice, and trip assignment
(AKA UTMS).
|
|
A mathematical construct that exhibits properties of self-similarity (the
same structure characteristics emerge at different spatial scales) that has
been applied to models of urban growth and development.
|
|
A general, quadratic programming algorithm commonly used in iterative
trip assignment to search for optimal weights of a convex combination
of successive linear approximations (i.e., AON assignments).
|
|
Essentially the same as the Furness method, Fratar's (1954)
method is a growth factor model to forecast a future trip
tables based on zonal growth factors and a base trip table.
|
|
A trip assignment algorithm that is not
capacity restrained, such as All-or-Nothing
or Dial's multipath assignment.
|
|
Same as free mean speed.
|
|
The average speed of vehicles traveling unimpeded on a section of roadway,
(AKA free-flow speed). The equivalent travel time
measure is base or free-flow travel time, the minimum time required to
traverse a section of roadway.
|
|
Freight Analysis Framework, a FHWA freight analysis tool
based on commodity flow surveys, includes weight and value estimates for
commodity movements by origin, destination, and mode; 30-year forecasts; and a
network database
[ web ].
|
|
Travel forecasting for freight, encompassing (a) forecasting
volumes and level of service for current and planned freight transportation
facilities and services, (b) evaluating the associated benefits and costs, and (c)
developing plans for system operations. Freight networks are usually integrated
with other modal networks and freight shipments often involve multiple actors,
increasing model complexity.
|
|
A generic term for all movements of goods via the highway and other modal networks.
Freight transportation, also known as goods movement,
has increased in importance in most metropolitan areas with the increase in network
congestion and air quality conformity requirements. The methodological field is
referred to as logistics.
|
|
A macroscopic freeway corridor simulation model. Current
version is FREQ12 includes models to analyze ramp metering and HOV lanes
[ web ].
|
|
INTRAS, a freeway simulation model developed by KLD in the
1970s, evolved into FRESIM that, together with NETSIM
(arterial simulation), formed the integrated software suite TRAF
(now TSIS/CORSIM).
|
|
Utilized in gravity trip distribution models as
empirical measures of travel impedance (a function of travel time
or generalized cost), friction factors (Fij)
are a frequent alternative to inverse power,
negative exponential, and combined (gamma)
impedance functions. In practice, friction factors are mapped into one minute trip
length categories related to the corresponding observed trip frequency.
|
|
The Federal Transit Administration, formerly
UMTA, in the branch of USDOT
responsible for federal funding for and technical support of the planning
and development of deomestic public transportation systems.
|
|
Federal Test Procedure
(see Federal Test Procedure).
|
|
The classification of roads by design function. Road classes higher in the hierarchy
place relatively more emphasis on service to through traffic and less emphasis on
serving local land uses. Classes lower in the hierarchy place increasingly greater
emphasis on access to local land uses. A sample hierarchy is freeways and other
limited-access facilities, arterials (primary,
secondary), collectors, and local streets.
|
|
Infrastructure (e.g., a bridge) that does not meet current design standards for geometrics
(see structurally deficient).
|
|
The three fundamental traffic flow variables, volume V,
density D, and space mean speed s, define the
fundamental traffic flow relationship ( V = D s ). The fundamental diagram
depicts this relationship graphically with the speed-density relationship defining
the shapes of the volume-density and volume-speed relationships. This diagram
provides a direct link between traffic engineering
(speed-density models) and travel forecasting
(performance functions).
|
|
A matrix modification method used to extrapolate trip distribution on the basis of
zonal growth factors and iterative proportional fitting (see IPF).
It can also be used to balance productions and attractions in the
singly-constrained gravity model.
|
|
Zadeh's (1965) alternative model of uncertainty where classification is defined
by rules that use subjective or approximate values applied to ambiguous objects
or concepts, utilized in AI applications in
traffic control.
|
|
| G | [ back to top ] |
|
|
An approach to modeling interactions between agents facing
strategic decisionmaking with imperfect information and varying incentives.
|
|
In gravity models, a variety of function forms have been used
for travel impedance in trip distribution,
including inverse power,
negative exponential, and combined gamma functions,
as well as the conventional friction factors.
The gamma function combines the inverse power and negative exponential functions:
f(tij) = μ0 tij-μ1exp(-μ2 tij)
|
|
Garin's (1966) modification of Lowry's
land use model, which introduced both a matrix formulation
and explicit spatial interaction models for activity location.
|
|
Taxes on gasoline and diesel fuel for vehicles using public roads include federal,
state, and local components. The federal excise tax is 18.4 cents per gallon
(independent of fuel price). In California, the state excise tax is 18 cents per
gallon. There are also state and local sales taxes on fuel. In California, the state
sales tax is 7.25 percent and several local counties have voted for additional sales
taxes dedicted to transportation (1.0 and 0.5 percent in LA and Orange counties,
respectively) [as of 1 January 2008].
|
|
A self-scaling statistic designed to compare link flow volumes over a range of
link types, named for its developer Geoffrey E. Havers. It is defined as:
GEH = √ [ 2(Ea-Oa)2/(0.5(Ea+Oa)) ]
where Ea and Oa are estimated and observed link volumes.
|
|
Traditionally used synonymously with biological sex, indicting male or female, but
increasingly associated with social constructs such as role in
the study of travel behavior.
|
|
The long-range plan for a community's future development, a general plan
(also known as a comprehensive plan or a master plan)
defines goals and objectives, policies and standards, and constraints for the
growth and development of the community. The plan provides a
land use and zoning plan indicating
planned land uses (e.g., residential, commercial, institutional) for districts
and parcels, and addresses all planning elements including
transportation infrastructure and services, the natural and built environment,
and demographic trends.
|
|
A weighted combination of the perceived attributes of travel cost
such as monetary cost, travel time (with component parts such as
access, waiting, and
in-vehicle time usually separated), and distance. May involve
composite general costs over alternate modes but not indirect costs of externalities.
See impedance.
|
|
A (freeway) lane open to all motor vehicles, unrestricted by tolls or
occupancy requirements.
|
|
Generic term for trip generation.
|
|
In discrete choice models, a generic variable appears in the utility
function of each choice alternative with the same estimated coefficient
(compare to alternative-specific variable).
|
|
Heuristic optimization algorithms that, borrowing from
evolutionary biology, use replication, mutation, recombination, and natural
selection processes operating on a parent population of potential solutions
to generate offspring that are evaluated based on a defined fitness function
to see which will be selected to form a new population to repeat the process
and move toward an optimal solution.
GAs have been applied to complex problems where evolutionary processes
can move potential solutions away from local optimums.
|
|
The rehabilitation or redevelopment of deteriorated, typically low income
neighborhoods with the resulting increased property values displacing the
original residents by new residents with higher socio-economic status.
|
|
The process of mapping activity locations reported in travel
surveys to a geographical coordinate system (e.g., latitude and longitude)
for use in travel forecasting. Geo-coding conventionally
assigns activity locations by TAZ number.
GPS automatically provides precise geo-coded location
data and is increasingly used in travel surveys.
|
|
Physical roadway design, including horizontal and
vertical alignment as well as
cross-sectional design, and incorporating basic
relationships decribing the interaction between drivers, vehicles, and
the roadway, to accommodate safe and efficient travel.
|
|
Generalized Extreme Value, a family of continuous
probability distributions that includes the Gumbel (GEV Type I) distribution
associated with the multinomial logit model.
|
|
GreenHouse Gas, (see GHG).
|
|
A measure of inequality on some population characteristic, usually income,
defined from 0 (perfect equality) to 1 (perfect inequality) and computed as
the area between the Lorenz Curve and the diagonal,
divided by the total area under the diagonal.
|
|
A Geographical Information System is an integrated spatial
database, analysis, and graphic display tool (such as ArcInfo or
TransCAD).
|
|
The increase in annual average temperatures at the earth's surface based on
various factors, including the increase in greenhouse gases
in the atmosphere due to the combustion of fossil fuels
[ see Climate Change ].
|
|
Gross National Product is the value of all the goods and
services produced in a country.
|
|
The first stage of the transportation planning process
is Problem Definition, which incorporates Goals,
broad statements based on community values and the current environment, and
Objectives, restatements of goals in specific and measurable terms.
Problems may be defined when objectives, often defined in terms of
performance measures, are not met by the current environment.
|
|
A measure of statistical performance that indicates how well a set of data is
described by a model estimated with that data.
|
|
The transportation of freight rather than people,
most commonly applied to movements within metropolitan areas rather than
within or between states or countries.
|
|
The Global Positioning System is a system of satellites
and surface-based receivers that can accurately determine location and time.
Increasingly utilized in traffic engineering and transportation modeling
applications, including in the conduct of travel surveys,
since GPS automatically provides precise, time-stamped geo-coding.
|
|
The percentage change in elevation to change in distance for a roadway section.
|
|
A transportation facility elevated above or trenched below another facility
to separate traffic movements, increasing capacity and safety. May involve
one or more transport modes.
|
|
An optimization algorithm used in path-based trip assignment
with some computational and theoretical advantages over link-based algorithms such
as Frank-Wolfe. Path-based algorithms
identify and store utilized paths in each iteration, which can limit practical
applications to smaller networks, but providing better estimates of turning
movements.
|
|
A trip distribution model that represents trip interchanges
as a function of trip productions, trip attractions,
and interzonal impedance (a function of interzonal travel cost, usually
defined by travel times). Singly and Doubly
constrained versions are in common use.
[ DCGM: Tij = ai bj Pi Aj f(tij) ]
[ SCGM: Tij = ai Pi Wj f(tij) ]
|
|
Any heuristic algorithm that makes locally optimal choices at
each step in search of a global optimum.
|
|
An increasing subjective buzzword implying concepts, products, processes,
services, or technologies that increase the efficient use of energy and
other resources and minimize the associated negative environmental impacts.
|
|
AASHTO's "A Policy on Geometric Design of Highways
and Streets", the standard reference on highway geometric design
[ web ].
|
|
The portion of a cycle for which signal
indications display green to permit a particular
movement (see also amber,
red, and effective green).
|
|
A non-linear single-regime traffic stream model developed by
Greenberg (1959), relates space mean speed to
density,
derived from the macroscopic hydrodynamic flow analogy,
and provides a bridge to microscopic car-following models.
Greenberg: u = um ln(dj/d) where
um is speed at maximum flow and dj is jam density.
|
|
Ambient temperature increase resulting from solar energy changing to
heat energy and captured within the earth's atmosphere.
|
|
Any gas, such as carbon dioxide, methane,
and nitrous oxide, that occurs naturally or through human activity, and
contributes to the greenhouse effect where heat is
trapped in the atmosphere and contributes to global warming.
|
|
A linear single-regime traffic stream model developed by
Greenshields (1935), relates space mean speed to
density and leads to a parabolic flow/density plot of
the fundamental diagram.
Greenshields: u = uf [ 1 - (d/dj) ] where
uf is mean free speed and
dj is jam density.
|
|
The basic geographical unit of a regional air quality dispersion model,
analogous to (but not necessarily corresponding to) zones in the regional
transportation model.
|
|
A network design pattern dominated by orthogonal streets, often hierarchically
designated, and typically with 4-way, right-angled, at-grade intersections.
|
|
Strictly defined as occurring on a grid network where
traffic heading in one direction is blocked from proceeding through an
intersection by queued cross traffic, traffic which itself may be blocked by
queued cross traffic at the next downstream intersection.
Queues spillback to block upstream intersections, "locking" the grid.
The term has become synonymous with "traffic jam", or a high level or duration
of traffic congestion, regardless of the presence of a grid.
Note: An alternative definition places gridlock as a synonym to deadlock,
a stalemate where no progress can be made, thus, to be stuck in place.
|
|
An in situ measurement of an observed quantity for use in evaluation or
validation of an estimate, model, or method. First used in military applications
and then applied in remote sensing, the term has been used
in the evaluation of sensors for intelligent transportation
systems and increasingly, and perhaps inappropriately, in transport modeling
and simulation, where ground truth is often defined rather than measured.
|
|
Residential units housing groups of unrelated individuals such as military barracks
or dormitories. Typically serves as a separate input in
trip generation analysis.
|
|
A trip distribution model that represents
trip interchanges
as a function of trip productions, trip attractions,
and a base trip table (in place of a matrix of interzonal travel times
such as in the gravity model). The base trip matrix is factored by
estimated productions and attractions. Growth factor models do not include LOS
variables (e.g., travel time), so practical applications are generally limited to modeling
external trips which have unknown total trip lengths. An example is
the Fratar model.
[Example: a doubly-constrained growth factor model: Tij =
ai bj Pi Aj Tijobs ]
|
|
Local government activities to minimize the negative impacts of development by
controlling the density, timing, and siting of new development to match available
transportation infrastructure and services.
|
|
Graphic User Interface.
|
|
A transportation facility with an exclusive mode- and grade-separated guideway.
|
|
| H | [ back to top ] |
|
|
A recurrent pattern of behavior resulting from frequent repetition, such as
the commute to work where the mode, departure time, and route may no longer
be a conscious choice.
|
|
Swedish geographer who formalized the field of Time Geography
and the representation of human activity with space-time prisms,
the three dimensional depiction of activity and travel over time and space that
reflected the capability, coupling, and authority constraints
that confine if not define movement.
|
|
Hansen (1959) developed a model to allocate residential growth constrained by
total regional growth and directly proportional to vacant land and employment
accessibility [2] (defined for each residential zone as the
sum of the ratios of employment to the square of distance from the residential
zone).
|
|
Highway Advisory Radio (see HAR).
|
|
In general, a statistical model relating an item's failure to time in service,
used in time use and activity-based analysis
to model activity duration.
|
|
Any material legally designated as capable of posing a risk to health,
safety, and property when stored or transported.
|
|
See Hazardous Material.
|
|
Home-Based Non-Work is equivalent to Home-Based Other
( HBO ).
|
|
Home-Based Other (also known as Home-Based Non-Work, or HBNW):
a classification for trips that either begin or end at a trip maker's residence
(home) and have the other end NOT at the trip maker's work location
(see HBW).
|
|
Home-Based Work: a classification for trips that either
begin or end at a trip maker's residence (home) and have the other end at the
trip maker's work location (see HBO).
|
|
Highway Capacity Manual (see HCM),
Highway Capacity Software (see HCS).
|
|
[1] The time interval (in seconds) between successive vehicles passing a
point on a section of roadway, usually averaged over a defined counting period.
Headway h is the inverse of volume V:
h = 3600/V in seconds/vehicle (see spacing).
[2] The time interval between successive arrivals of transit vehicles at
a fixed location.
|
|
A land use allocation model developed by Herbert and Stevens (1960) for the
Penn-Jersey Transportation Study using a linear programming
framework.
|
|
The Highway Economic Requirements System
( see: HERS ).
|
|
The matrix of all second-order partial derivatives of a specified function,
used in optimization search routines with the Jacobian
matrix of first derivatives.
|
|
Problem solving via replicable, experimental techniques such as trial and error,
rule-based systems, and various search methods (including
hill-climbing and genetic algorithms). Heuristic
approaches do not guarantee a optimal solution, thus, they are usually selected
only when formal mathematical models can not be applied.
|
|
See nested logit model.
|
|
Low emission, energy-efficient, high-technology rail systems. Planning in the US
envisions systems with average speeds of 100-150 mph (or higher) operating on
dedicated or shared, grade-separated track in defined intercity corridors.
|
|
Low-powered radio stations operated by transportation agencies to provide local
traveler information regarding incidents, congestion, construction, special events,
and other delays.
|
|
Standard guidelines and procedures for roadway and intersection capacity design
and analysis, developed by TRB, AASHTO,
and FHWA. Implemented in Highway Capacity
Software (HCS)
[ HCM web,
HCS web ].
|
|
The software implementation of the Highway Capacity Manual (HCM),
developed by TRB for roadway and intersection capacity design and
analysis [ HCS web ].
|
|
The Highway Economic Requirements System (HERS) models the relationship between levels
of investment in and the performance of the highway system. It is linked to the Highway
Performance Monitoring System ( HPMS ).
[ web ].
|
|
The Highway Performance Monitoring System is a
federally-mandated database consisting of facility design and performance data
for highway links which is used to track the characteristics, performance, and
condition of the nation's highway system
[ web ].
|
|
The federal trust fund that collects and allocates highway user taxes and fees
such as the federal motor fuel tax. The fund is used to provide federal support
to both highway and transit projects.
|
|
The area defined by the sphere of influence associated with an activity center.
See Central Place Theory and von Thünen's
model.
|
|
An efficient solution algorithm to the Transportation Problem
that utilizes the dual of the linear programming formulation
to obtain a single-commodity, uncapacitated, minimum costs flow solution.
|
|
Highway Land Use Forecasting Model developed by
Horowitz (1993) based on a Garin-Lowry framework and
sharing model components and utilities with QRS-II.
Similar land use software packages include MEPLAN,
MUSSA, PECAS,
TRANUS, and UrbanSim.
|
|
September 3, 1967, the day that Sweden changed from driving on the lefthand
to the righthand side of the road, to match neighboring countries.
|
|
Home is an individual's residential housing unit and location.
Most travel surveys are home-based, sampling households by
residential location, in part since most trips are home-based.
Home (or Return Home) was often used as a trip purpose in travel surveys.
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A classification for trips that either begin and/or end at a trip maker's
residence (home). Regardless of the origin and
destination, the home location is always the
production for home-based trips; the other end is always
the attraction (see Non-home-based).
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A trip with one end at home and the other end at a non-work location
(see HBO).
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A trip with one end at work and the other end at home
(see HBW).
|
|
A legacy term for a household travel survey, conducted
by interviewers in the home of the survey respondent. Largely replaced by
CATI interviews and self administered
surveys.
|
|
A reactionary term created and applied after the September 11th attacks referring
to the consolidated efforts to protect the US from perceived threats to national
security (also refers to the newly created cabinet department).
|
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The design of a roadway alignments in the horizontal plane, including tangent
sections, circular curves, and spiral transition curves, and reflecting
topography, safety, facility type, speed, and other design concerns (see
vertical alignment and
cross-sectional design).
|
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A High Occupancy Toll Lane is a managed
lane reserved for high-occupancy vehicles (HOVs) and for non-HOVs
that pay a toll to use the facility.
|
|
Emissions that occur after a hot engine has been turned off.
|
|
A hot start occurs when a vehicle's engine is started after less than an hour
from the previous period of operation (see cold start).
|
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A fundamental sampling unit for travel surveys, the
household (HH) is a behavioral unit of one or more individuals who share
a dwelling unit, resources (e.g., income, automobiles), and
travel/activity responsibilities. Interaction among HH
members influences travel and activity behavior.
Most trip production models are household-based.
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Individual decision-making and the resulting activity and travel behavior
is facilitated by household resources and constrained by
responsibilities to the household. HH interactions are in part defined
by HH life style and individual roles.
|
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A survey designed to measure household travel behavior and
the characteristics of the household that are relevant to its travel behavior.
The survey typically collects information on the household, household members,
household vehicles, and a travel activity diary that records
all activity and travel that occurs during the survey period. Typically conducted
in metropolitan areas every 10 years.
|
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Same as dwelling unit.
|
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High-Occupancy Vehicle, that is typically 2 or more (sometimes
3 or more) occupants (see SOV). HOV lanes
are dedicted facilities for the use of HOVs only (with exceptions such as motorcycles
or electric vehicles, or for off-peak periods in some regions).
|
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A High Occupancy Vehicle lane is more commonly known as
a carpool lane.
|
|
The Highway Performance Monitoring System
( see: HPMS ).
|
|
High Speed Rail (see HSR).
|
|
A vehicle that combines two propulsion systems, typically an electric motor
and an internal combustion engine, to improve efficiency
and decrease emissions.
|
|
Compounds containing carbon and hydrogen that are the primary components of
fossil fuels as well as forming emissions from the
incomplete combustion of fossil fuels, some HCs are major air pollutants.
|
|
Kinematic wave theory, introduced by Lighthill and Whitham (1955)
is a macroscopic theory of traffic flow based
on analogy to continuous, incompressible fluid flow:
∂k/∂t + (∂q/∂k)(∂k/∂x) = 0 where
∂q/∂k is the speed of the shock wave and
where k = density (vpm); q = volume (vph); t = time (min); and x = distance (miles).
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An hypothesis is a proposition for which a test of validity is to be
performed. The null hypothesis (H0) is a testable hypothesis:
one for which a sampling distribution can be defined. This is typically a
proposition that no relationship exists between variables of interest.
Hypothesis testing is the process of attempting to reject H0, thus
accepting the alternative hypothesis that the estimated relationship
is valid.
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[1] The failure of a system to return to its initial state after a temporary shock
[2] The system property of a time lag between a cause and an effect.
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| I | [ back to top ] |
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International Association of Travel Behavior Research,
an international association promoting research on activity and travel behaviour,
including the organisation of triennial conferences on travel behaviour research.
[ web ].
|
|
International Association of Time Use Research,
an international forum to promote time use data collection, analysis, and
dissemination of research results
[ web ].
|
|
Internal Combustion Engine (see ICE).
|
|
Information and Communications Technology (see ICT).
|
|
Intersection Capacity Utilization, a simple technique used for
measuring intersection capacity based on critical movements analysis.
Designed for planning applications in site impact studies and roadway design, versus
delay-based methods for operations and signal design (such as HCS
and SYNCHRO).
|
|
Institute of Electrical and Electronic Engineers,
or "I-triple-E", is the professional society whose role in transportation is
the advancement of information technologies and communication standards
(e.g., 802.11).
|
|
Independence from Irrelevant Alternatives
( see ILD ).
|
|
Independently and Identically Distributed.
|
|
Inductive Loop Detector ( see ILD ).
|
|
Intended or unintended effects on the natural and built environments as a result
of operation or implementation of transportation infrastructure and services.
|
|
Fees assessed by municipal or regional government and charged to developers to
mitigate for the degradation in traffic performance caused
by the impacts of a particular proposed development project.
Fees are based on established performance standards and/or the cost of the
mitigation strategy.
|
|
Impedance, a computed measure of the disincentive to travel due to spatial
separation, is a composite function of travel time (often
split by access, in-vehicle, and
egress time), travel cost, and/or
distance. Commonly utilized as only a function of
travel time. Also known as deterrence
or generalized cost (see skims).
|
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An efficient means of storing network topology relationships, including
node-link and link-path
incidence matrices.
|
|
A nonrecurring event that affects transportation system performance, including
traffic accidents, disabled vehicles, roadway maintenance activities, and other
flow disruptions.
|
|
Application of ITS methods and technologies to
detect, identify, respond to, and manage traffic incidents in real-time.
|
|
The log of the logit model denominator and equivalent to the
expected utility of the choice being modeled. Also known by the descriptive term
logsum, the inclusive value is a summary measure of the
desirability of the entire choice set and is directly connected to conventional
welfare measures. In nested logit, the inclusive value is a
component of the utility of the composite alternative
representing a particular nest in the higher level of the choice structure.
|
|
A trip assignment algorithm that loads predetermined increments
of a trip table onto the minimum paths, then recalculates minimum paths and
assigns the next increment, accumulating increments of volume at each step.
This technique can produce results approximating UE solutions
but determining the best set of increments can be difficult.
|
|
Incremental elasticity analysis facilitates application of
elasticities to "what if" scenarios, by expressing the change in demand "D" as a
function of the change in service "s" level and the associated elasticity, or:
[ ΔD = eD|s • D • Δs / s ]
|
|
A quick response application of logit models where an estimated
model, current market shares, and the proposed change in a specific policy variable
are used to directly estimate policy impacts in lieu of a full model application,
|
|
IIA is a mathematical property of logit models where the
ratio of choice probabilities for any two alternatives in independent of the presence
of any other alternatives (see Red Bus / Blue Bus problem).
|
|
An exogenous variable hypothesized to influence the value of a
dependent variable (i.e., an explanatory
variable). The term independent draws from the OLS
assumption that multiple exogenous variables must be uncorrelated with each other
(i.e., independent).
|
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INDEX is a GIS-based software package that analyzes and graphically presents
the impacts of alternative planning scenarios using a range of design measures
(such as the 5 Ds). INDEX estimates travel impacts such as
changes in vehicle-trip rates and VMT and
can be applied at spatial scales ranging from neighborhoods to regions. It was
developed by Criterion Planners [ web ]
based on the public-domain PLACE3S.
|
|
The illumination of one or more signal displays, such as a green arrow and a
green ball allowing for left turning and through movements on a given approach
to proceed.
|
|
A graph of the relative demands for two goods for which the
utility derived remains the same and thus for which the
consumer has no choice preference (AKA iso-utility curve).
|
|
An elasticity defined as the change in market share of an
alternative due to a change in an attribute of a competing alternative (e.g., the
change in transit demand due to auto fuel price increase). Also called a cross
elasticity. Compare with direct elasticity.
|
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Travel demand generated by increased capacity or
decreased price. The induced demand may represent trips that have been
made to other destinations, by other modes and routes, and/or at other times,
now reflected in a new travel choice in response to improved local performance,
as well as representing new (latent) demand on the network.
New demand can be associated with socio-demographic growth or may simply be
demand that was suppressed by prior costs of travel.
|
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A solenoid loop of wire embedded in roadway pavement and connected to a
sensor that records vehicles breaking the magnetic field
above the loop. For a defined counting interval, the sensor
typically records the number of such activations (count) and
the proportion of time that the activation occurs (occupancy).
|
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An infill area contains vacant land parcels surrounded by developed parcels.
Associated infill development may be planned to increase the density or land
use mix to address policy goals such as smart growth.
|
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The full range of technologies for the generation, collection, archiving,
processing, and communication of information, including software and hardware
systems, ICT can complement and/or substitute for transportation
(see IT).
|
|
INstitute For Operations Research and the
Management Sciences, the international professional society
in operations research and management science
[ web ]. The Transportation Science
and Logistics section focuses on OR applications in these special areas
[ web ].
|
|
The built environment -- in transportation, the components of the modal
networks, terminals, and
control systems that comprise the physical
transportation system.
|
|
An economic analysis acounting system that extends the economic base
model to depict the flow of goods and services (represented in monetary or employment
terms) within a region (or between regions). IO traces the required inputs to
a particular economic sector and the distribution of outputs (to intermediate and
final demands) via a matrix approach to provide employment projections and economic
impact assessments.
|
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Institut National de REcherche sur les Transports
et leur Sécurité, the French nationally-sponsored institute for transport
and safety research [ web ].
|
|
The spatial nature of transportation infrastructure and services over multiple
jurisdictions and/or agencies often creates problems of
institutional coordination, with different stakeholders
having different managerial, operational, and financial policies. Efficient
transportation systems require meaningful interaction between stakeholders in
planning and development, design and construction, and management and operations.
|
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Urban Model was used synonymously with land use model,
but as travel forecasting models were integrated into land use
models, and as land use models evolved to better reflect land use economics, the
resulting term became integrated urban model.
|
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The trip-based traffic microsimulation model that addresses freeways and
arterials, as well as traffic assignment, simulation, and optimization.
|
|
Buzzword for a group of Vehicle Infrastructure Integration (VII)
initiatives that provide drivers with improved situational awareness of event and
hazards within the vehicle's environment.
|
|
An increasing trite buzzword implying a process or technology that facilitates
transportation planning, design, or management, or increases the efficiency of
transportation operations. Similar terms include "smart"
and "advanced".
|
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Infrastructure with integrated sensors and adaptive controls
that sense the environment, assess system status, and actively or passively manage
and control.
|
|
Advanced methods and technologies to improve performance of existing
transportation capacity, including
Advanced Transportation Management Systems ( ATMS ),
Advanced Traveler Information Systems ( ATIS ), and
Advanced Vehicle Control Systems ( AVCSS )
(ITS, formerly IVHS).
|
|
A location-based sampling frame and survey. External surveys
sample drivers at external stations to obtain basic O-D data
(either roadside interviews or recording license plates for later contact).
Transit on-board surveys sample transit users on transit
vehicles for transit use surveys.
|
|
Between cities, versus "intracity" meaning within a city, often referring to
intercity rail service operated in the US by Amtrak,
distinguished from intracity rail transit operations serving urban corridors.
|
|
Transportation planning or operations that involve more than one
mode of transportation. Sometimes taken as the operational
aspect that involves direct interactions between modes (such as in passenger
or freight transfers). See also multimodal.
|
|
In traffic impact analysis for mixed-use
developments, internal capture is the proportion of trips attracted to a
particular parcel that are drawn from other parcels in the development, thus
reducing the site's traffic impact on adjacent streets (see also
pass-by trips). The design of sustainable communities is
in part based on a land use mix that accommodates internal trips being made by
public or non-motorized modes or with shorter trip lengths.
|
|
The motive power of the majority of current vehicles is provided by the
combustion of fuel and air within an engine, which transfers the resulting
mechanical motion to the vehicle drive train.
|
|
In project appraisal, the effective annual compound
interest rate that yields a net present value of zero
(a benefit cost ratio of 1.0), providing a measure of
investment efficiency.
|
|
A trip with both its origin and its
destination located inside of the study area.
If either trip ends is outside the study area, it is an external trip.
If both trip ends are outside the study area, it is a through trip.
|
|
The ability of multiple systems to efficiently exchange and utilize information,
interoperability applies to general systems and organizations but has been
most commonly referenced with respect to communication systems in transportation.
|
|
Capacity analysis for uncontrolled, sign-controlled, or
signal controlled intersections, a key stage in traffic impact
analysis.
|
|
The time period during which all signal indications
on all approaches remain the same.
|
|
A scale used to measure a variable for which the intervals between values are
defined but with an arbitrary zero point. An example in travel
forecasting in departure time. See measurement scales.
|
|
An infrequently applied alternative trip distribution model that
probabilistically estimates destination choice as a function of the number of
activity options available between the trip origin and any given destination zone.
|
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Between two different analysis zones (versus intrazonal,
or within a zone).
|
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Within a single analysis zone (versus interzonal,
or between zones).
|
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A trip with both origin and destination
in the same zone. In trip assignment, intrazonal trips are not
loaded on the network.
|
|
The portion of a trip that occurs while traveling in a vehicle as opposed to the
out-of-vehicle portion that includes access,
waiting, transfer, and egress times). Disutilities are in general
lower for in-vehicle time.
|
|
A way-finding technology for automobiles that combines a map database (often on
a CD) with a graphic and/or audio user interface, typically integrated with a
GPS to provide drivers with real-time directions, and potentially
integrated with a cellular feed to provide real-time traffic conditions.
|
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A term used in the past for the process and results of a comprehensive
cataloging of existing conditions in a study area,
including transportation infrastructure and services;
traffic volumes and level-of-service by mode; land use;
and transport impacts (noise, emissions, etc.), which
serve as basic inputs to the transportation modeling process.
|
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In gravity models, a variety of function forms have been used
for travel impedance in trip distribution,
including inverse power, negative exponential, and
combined (gamma) functions, as well as the conventional
friction factors. The inverse power function results
from assuming a logarithmic total cost constraint in the
entropy maximization derivation:
f(tij) = tij-μ
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Iterative Proportional Fitting (see IPF).
|
|
The Intermodal Surface Transportation Efficiency
Act of 1991, the federal transportation authorization
that continued the series of Federal Aid Highway Acts
but incorporated significant revisions to metropolitan and statewide planning
processes, emphasizing an intermodal approach and
strengthening the role of metropolitan planning organizations
in the overall planning process. ISTEA also implemented the Congestion
Mitigation and Air Quality Improvement Program
(CMAQ).
ISTEA was followed by TEA-21, the
Transportation Equity Act for the 21st Century (1998),
and SAFETEA-LU, the Safe, Accountable,
Flexible, and Efficient Transportation Equity
Act -- A Legacy for Users (2005)
[ web ].
|
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Information Technology is the design, development, implementation,
and operation of computer-based information software and hardware systems.
|
|
The Institute of Transportation Engineers, an
international association of transportation professionals directed primarily
toward planning, design, implementation, and operations of transportation
infrastructure and services [ web ].
|
|
The ITE Trip Generation report is a compendium of
trip generation rates primarily used in
traffic impact studies. Average rates and estimated models
are provided by land use, time period, and a variety of explanatory variables.
|
|
A procedure that repeats calculations in a loop but does not utilize self-reference
as in a recursive procedure. Whereas a recursive procedure F(n)
to compute factorial (n) would itself call F(n-1), an iterative procedure
would call F(n) from a main program for each separate evaluation of n. Both imply
a cascading process where the output of one step is the input to the next.
|
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A family of trip assignment algorithms that solve for optimal
flows via iterative application of an elementary loading algorithm
(e.g., All-or-Nothing Assignment). The results of two successive
iterations are combined to find the volumes and corresponding
travel times for the next iteration (e.g., see Frank-Wolfe or
MSA).
|
|
A technique to generate population cross classification cell
frequencies, given marginal population frequencies, consistent with sample cross
classification cell frequencies. IPF is used in the generation of
synthetic populations for activity-based
models.
|
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Integrated Transportation and Land Use Package
is a land use model software package, integrating the DRAM/EMPAL
spatial interaction models, and applied in many metropolitan transportation studies
over the past few decades (Putman, 1983). Other land use software packages include
MEPLAN, MUSSA,
PECAS, TRANUS, and
UrbanSim.
|
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[1] The Institute of Transportation Studies of the
University of California [ web ]
[2] Intelligent Transportation Systems
(see ITS)
[ web ].
|
|
National organization advocating the development and application of advanced
technologies for surface transportation (e.g., Intelligent Transportation Systems,
ITS), comprising private firms, public agencies, and academic
institutions [ web ].
|
|
A structural framework defining the interrelationships between intelligent
transportation system (ITS) components.
|
|
Intelligent Vehicle Highway Systems, now referred
to as ITS.
|
|
In-Vehicle Navigation System (see IVNS).
|
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| J | [ back to top ] |
|
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The vector of all first-order partial derivatives of a specified function
(see Hessian).
|
|
A facility's maximum density (vehicles per mile), where
spacing and space mean speed approach
zero (when cars are "bumper to bumper").
|
|
A form of paratransit characterized by smaller vehicles
operating on a fixed route but stopping anywhere for boarding/unboarding and
not running on a fixed schedule. Compare with conventional
or demand-responsive transit operations.
|
|
The spatial distribution of employment relative to the distribution of workers
(by residence) within a defined area. An area with a balance of jobs and housing
would imply a greater likelihood that a worker would find a job nearby, minimizing
commute trip length. Variations in job and worker types require a concise definition
of balance as having complementary job and housing characteristics.
|
|
Coordinated public and private sector land development, typically around transit
stations, with the public sector offering development incentives in return for
the private provision of transit-compatible development.
|
|
The trip to work (AKA commute).
In the decennial census, the associated distributions of mode
and travel time.
|
|
A level of government (city, county, state, or federal) or regulatory authority
(local, regional, state, or federal) responsible for some or all aspects of the
planning, implementation, operations, and maintenance of transportation facilities
and services in a defined area.
|
|
An inventory control strategy where resources are delivered precisely when
necessary, minimizing inventory costs, but potentially resulting in service
problems when variation in demand is not fully anticipated.
|
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| K | [ back to top ] |
|
|
[1] Adjustment factors sometimes applied to trip distribution
gravity models in an attempt to replicate specific trip table
cell-to-cell flows. These factors attempt to capture aspects of travel behavior that
are not captured via productions, attractions,
and impedance, but it is difficult to assess the impact of
these factors in forecasting. Some sources recommend limited use of K-factors
where needed, while other sources recommend a more liberal use to improve the fit
of a base model.
[2] The design hour volume (DHV) expressed as a percentage of
the annual average daily traffic (AADT).
|
|
A class of filters (recursive algorithms) for predicting or smoothing
time series data, used with traffic detector data for travel time and
OD estimation.
A Kalman Filter estimates a linear process via feedback control with a
state equation projecting system variables and a measurement equation providing
feedback by incorporating new data in the estimation process. Non-linear state
and measurement equations need an extended Kalman Filter.
|
|
The necessary conditions for an optimal solution to a constrained
non-linear program.
|
|
Introduced by Lighthill and Whitham (1955) and Richards (1956), kinematic wave
theory is a macroscopic theory of traffic
flow based on analogy to continuous, incompressible fluid flow, or:
∂k/∂t + (∂q/∂k)(∂k/∂x) = 0 , where
∂q/∂k is the speed of the shock wave and
where k = density (vpm); q = volume (vph); t = time (min); and x = distance (miles)
(also known as the hydrodyanamic analogy).
|
|
See Karush-Kuhn-Tucker conditions.
|
| American economist (1885-1972) and a founder of the Chicago school who formulated
early arguments for toll roads and a statement for traffic equilibrium in 1924
(which led to Wardrop's principles in 1952).
|
|
A software system that incorporates quantitative and qualitative professional
expertise and judgment in a database integrated with an inference engine to
emulate the decision process of experts in a particular area
( also know as Expert System ).
|
|
A geostatistics technique similar to least squares regression that interpolates
values for unsampled locations from observed data at neighboring sampled locations.
|
|
A variant of the minimum path problem where the shortest path,
the 2nd shortest, through the kth shortest are found. Algorithms include the
Double Sweep and generalizations of Dijkstra's and Floyd's single path algorithms.
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| L | [ back to top ] |
|
|
Minimum path algorithms assign node labels
based on cumulative travel time from the origin node. Algorithms such as
Moore's or Floyds correct
node labels at each iteration as better paths are found (compare with
label-setting algorithms). Labels are final only after all
nodes have been precessed (some processed multiple times).
|
|
Minimum path algorithms assign node labels
based on cumulative travel time from the origin node. At each iteration, algorithms
such as Dijkstra's set the label for the node closest to
the origin as permanent thus adding it to the minimum path tree
(compare with label-correcting algorithms).
|
|
Workers defined by residential location, versus employment
defined by job location.
|
|
A left-turn phase that begins after the start of the approach's
thru movement (see leading left).
|
|
A solution method for constrained, non-linear, optimization problems. Each
constraint is multiplied by a scalar Lagrange Multiplier and is added to
the original objective function, changing a problem with N
variables and M constraints to a problem with N+M variables and no constraints.
The multiplier indicates the amount the objective function will change with a unit
change in the corresponding constraint (see shadow price).
|
|
The primary activity for which a parcel of land is used (residential, commercial,
industrial, open space, undeveloped, etc.). Municipal zoning
and general plans identify legal designations of current and
planned land use.
|
|
Description of the amount of land for specified land use
designations, defined spatially by various zoning systems (e.g., parcels,
TAZs). Amounts may be represented in areal units (e.g., acres),
by activity descriptors (e.g., number of housing units), or densities (e.g.,
population per square mile). In travel forecasting, land use
data includes these quantitative and quantitative attributes as well as
demographic and socio-economic data that
describe the population utilizing the land in question. Together these define
the activity system.
|
|
One of an extensive range of quantitative models and procedures that describe
land use patterns (the activity system) of a region. These
models typically describe and predict the spatial distribution of population
and employment, and the corresponding land consumed. While transportation
networks are typically incorporated in the activity location
sub-models, historically, land use models were not fully integrated with
travel forecasting models. However, recently developed land
use models such as MEPLAN, MUSSA, and
UrbanSim are integrated land use transportation models.
|
|
One lane-mile corresponds to a mile-long segment of a single lane.
Total lane-miles is a measure of total road infrastructure capacity.
Compare to center-line miles.
|
|
Travel demand is a relationship between the price of
travel and the quantity of travel demanded. Travel that corresponds to that
part of a demand relationship that is not being realized due to limited
capacity and/or high price is considered latent demand (observed
travel may increase as these constraints are relaxed).
See also induced demand.
|
|
A criteria pollutant, lead (Pb) is a stable, heavy
metal that had been used extensively (e.g., in paint, batteries, and pipes)
but is highly poisonous to humans and animals.
|
|
A signal phasing plan with a leading left turn opposed
by a lagging left turn.
|
|
A left-turn phase that begins before or simultaneously with the approach's
thru movement (see lagging left).
|
|
Light Emitting Diode (see LED).
|
|
Leadership in Energy and Environmental Design is a
system for ranking infrastructure projects based on environmental sustainability.
|
|
A generic term for older versions of software, technologies, etc.
|
|
Low Emission Vehicle: a vehicle with emission levels
below a threshold based on standard vehicles.
|
|
[1] A set of quantitative or qualitative measures of transportation system
performance. The Highway Capacity Manual defines
levels of service (LOS) for traffic operations as ratings
ranging from A (best) to F (worst).
[2] In Transportation Systems Analysis (TSA),
performance functions model LOS as a function of system
characteristics (such as speed and capacity)
and link volume.
|
|
An individual possessing a legal license to drive a vehicle on public roads.
The number of licensed drivers in a household is strongly correlated
with the total number of generated trips; individual mode choice is
strongly correlated with possession of a drivers license.
|
|
LIght Detection And Ranging, a
remote sensing technology, locates objects on a
principle similar to radar but using light from a laser.
|
|
[1] Life style reflects an individual's or household's activity and travel
preferences, needs, and constraints as a function of demographic,
socio-economic, and geographic characteristics. The progression
through various life styles is termed the life cycle (childhood, living alone,
married couple, married with children, etc.) and role is the social position
held by an individual in a particular life cycle stage (single adult, parent, etc.).
[2] The total productive time span of a system from construction to salvage, often
reflecting the associated costs and benefits over that time period.
|
|
An engineering economics analysis tool to evaluate the lifetime economic
consequences of mutually exclusive project alternatives.
|
|
An energy-efficient, long-lifed, micro-electronic device for traffic signal
and CMS displays.
|
|
An estimated value of the likelihood function, for a
given set of parameters, providing a measure of the probability that
the model replicates an observed distribution.
|
|
A mathematical expression, usually expressed as a log likelihood, that
indicates the probability that a model with a given set of parameters
would replicate the observed choices of a sample, or:
L(β) = Σn log f( xn | β).
See maximum likelihood estimation.
|
|
A test of model significance in maximum likelihood estimation
and analagous to the F-test in regression,
the likelihood ratio compares the log likelihood of an
estimated model [L(β)] with that for the null hypothesis that all model
parameters equal zero [L(0)], with the resulting statistic, LR, being chi-square
distributed: LR = 2 [ L(β) - L(0) ]
|
|
Measures the degree to which a survey respondent agrees or disagrees with the
question being asked.
|
|
In the functional classification of roads, limited-access
facilities such as freeways, expressways, and tollways place primary emphasis
on service to through traffic rather than local land access. Facilities are
typically grade-separated and without traffic control (other than at access/egress
points such as ramps). Interchanges are usually limited to other limited-access
facilities and arterials. Arterials and limited-access
facilities account for less than 10 percent of the lane-miles
in the US, but almost 75 percent of the VMT. In travel forecasting
networks, limited access facilities are virtually always coded, often with great
detail regarding directional separation and interchange geometry.
|
|
The portion of a commute trip associated with the largest segment of total travel
time or distance. For an individual who drives a short distance to a Park and
Ride lot, then takes and express bus 30 miles to an activity center and walks
5 minutes to a work place, the express bus portion is the line-haul portion.
Typically refers to mass transit systems such as commuter rail or express bus.
See access and egress.
|
|
Point, line, and area sources
are idealized zero-, one-, and two-dimensional locations that are sources for
various pollutants. Roadway links are line sources for both noise and air quality
pollutants.
|
|
A mathematical optimization problem with a linear objective function and
linear constraints. In trip assignment, while the
all-or-nothing formulation is a linear program,
UE and SO formulations have
non-linear objective functions and linear constraints.
|
|
A fundamental element of a transportation network defined by a starting and
an ending node and having attributes such as length,
travel time and/or speed, and capacity. Represented in travel forecasting
models by link performance functions.
|
|
Conventional traffic assignment formulations assume that
link performance functions are independent (a link's
performance is dependent only on that link's volume), but interactions
occur at intersections as well as with "rubbernecking" on freeways. Algorithms
available in conventional software do not reflect the associated effects.
|
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A matrix of network topology containing M (links) rows and K (paths) columns (for one or more
origin-destination pairs) with each element equal to one if link m is on path k for a given
OD pair (and zero otherwise). A column k thus identifies all of the links on path k; a row m
thus identifies all of the paths k that contain a given link m (see:
incidence matrix ).
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A journey by transit from an origin to a destination may have multiple segments
that are completed on different vehicles or modes. While each segment involves a
transfer between transit vehicles or modes, the overall O-D travel is considered
one linked trip even though it produces multiple transit boardings (and
thus multiple unlinked trips ).
|
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A volume-delay function, a functional performance relationship
between level-of-service (e.g., travel time) and
link volume for a specific facility. The classic example is the
BPR link performance function.
|
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The environmental quality of a community as perceived by residents, employees,
and visitors. The environmental qualities include social, cultural, aesthetic,
ecological, and other aspects of the community. From a transport perspective,
livability reflects the quality of transportation alteratives available and
the impacts of those alternatives on the community.
See also person-environment fit.
|
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For a transportation vehicle, route, or other service, the ratio of
capacity utilized to total capacity.
|
|
The assignment of O-D demands to a network.
A generic term for trip assignment.
|
|
A level of government or regulatory authority responsible for some or all aspects
of the planning, implementation, operations, and maintenance of transportation
facilities and services for a local area (e.g., city or county).
|
|
The phrase local models (or travel models used at the local level)
may be interpreted as:
(a) models that are developed by city or county agencies and/or are applied at the
city or county level (although increasingly reflecting regional model
characteristics) and/or
(b) alternate models that are directed toward capturing traffic impacts of
evolving land use policies at the local level (contrast with regional
land use models).
Local models provide inputs to micro-simulation analyses; to infrastructure and
control system design; and to planning, investment, and operation decisions,
including the review of the effects of local land use projects, general and
specific plans, and other transportation system elements.
|
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In the functional classification of roads, local streets
provide access to local land uses. Local streets are low speed and low capacity
and often lack signalized traffic control. Local streets account for about two
thirds of the lane-miles in the US, but less than 10
percent of the VMT. In travel forecasting networks, local
streets often are not coded but are indirectly represented by
centroid connectors.
|
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The specific project that is selected by the lead agency following the completion
of a Major Investment Study (or any Alternatives
Analysis process). Also known as the Locally Preferred Strategy.
|
|
A sectoring method used in economic base analysis to estimate
the proportion of basic employment by economic sector, assuming
that local demands are met by a level of economic activity proportional to that in
a larger, reference economy, with remaining activity being basic.
|
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[1] While the assumption of unconstrained natural increase of a population yields
the exponential growth model (Malthus, 1798), an assumption
of finite resources yields the logistic growth model where growth is a
linearly decreasing function of the current population (Verhulst, 1838), resulting
in an S-shaped growth curve.
[2] A logistic map results from the discrete version of the logistic growth
equation that exhibits chaotic behavior (the resulting
bifurcation diagram is a fractal).
|
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The component of supply chain management involving the
planning, implementation, and control of processes for product distribution.
Supply chain management has taken on the broader definition that encompasses
the full production chain from raw materials to final consumption, usually
involving multiple actors. The term logistics is often used when
referring to operations research and other tools used in
the analysis and design of logistic systems.
|
|
A discrete choice model that assumes an individual maximizes utility in choosing
between available alternatives. The logit model's utility function comprises
a deterministic component (which is a function of measurable characteristics of the
individual and of the alternatives in the individual's choice set) and a stochastic
component (or error term) assumed to have an extreme value distribution
(see also Probit Model; Nested Logit Model).
|
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For logit models, the log likelihood function is the
sum over all individuals of the log of each individual's estimated probability
for the observed choice alternative. In maximum likelihood
estimation, the log of the likelihood function is maximized
by differentiating with respect to model parameters and employing an iterative
process to update parameters.
|
|
Models formulated as a linear relationship between independent variables and
the logarithm of the dependent variable.
|
|
The log of the logit model denominator, equivalent to the expected
utility of the choice being modeled, and thus used in nested logit
models (see inclusive value).
|
|
A survey of and data from a sample of observations collected at
repeated points over a period of time. Compare with cross sectional
surveys and data.
|
|
The Long Range Transportation Plan (LRTP) is a regional
(or statewide) consensus plan that defines the region's (or state's) transportation
system and planned improvements scheduled for funding over the next 20 years.
|
|
In transportation planning, a time frame of generally 20 years, corresponding
to the long range transportation plan horizon.
|
|
In travel forecasting software, link speed and capacity can be
coded individually for each network link or by using a look-up table that
provides default speed and capacity for links
defined by facility type and area type.
|
|
Common name for an Inductive Loop Detector ( see ILD ).
|
|
In network algorithms, a list of nodes which have been reached and processed.
In minimum path algorithms, the list contains nodes reached
but not permanently labeled.
|
|
A graph of some cumulative population distribution, often income, showing the
cumulative percent of the characteristic (income) versus the cumulative percent
of households (see Gini Coefficient).
|
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Level of Service (see LOS).
|
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A Low Occupancy Vehicle is the complement of an
HOV, or high-occupancy vehicle, and a more general term
for a SOV, or single-occupant vehicle, as the definition
of required HOW-occupancy evolves from 2 or more to 3 or more.
|
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One of the first large-scale urban land use models, the
Lowry Model (1964) combined an economic base model with
spatial allocation models to generate and allocate population
and service employment, within constraints on land
availability and compatible land uses
(see the Garin-Lowry Model).
|
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Link Performance Function (see LPF).
|
|
Liquid Propane Gas.
|
|
Long Range Transportation Plan (see LRTP).
|
|
The Land Use TRansportation Air Quality study
was commissioned by the 1000 Friends of Oregon to analyze alternative land use
patterns and design standards, and to estimate the associated transportation
impacts (e.g., mobility, air quality,
energy consumption).
|
|
Land Use Transportation Integrated Model,
developed by Mann (1995), is a Lowry-type land use model integrated with a
four-step transportation planning model.
|
|
A macroscopic theory of equilibrium
traffic flow developed by Lighthill and Whitham (1955)
and Richards (1956) based on analogy to continuous, incompressible fluid
flow (also known as Kinematic wave theory).
|
|
A "shared economy" technology firm that provides transport
services for profit where the economic transaction ("sharing") is between the technology
provider, a contracted physical provider, and a customer paying for the service.
(see also Uber). The technology is a smart phone application that
links customers seeking immediate transportation with affiliated drivers in the vicinity.
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| M | [ back to top ] |
|
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A model that describes system operations in aggregate terms (using TAZs
in four step models or using platoons for traffic flows)
(see Microscopic Model; see also aggregate).
|
|
A Major Investment Study (MIS) is an evaluation of the
cost-effectiveness of alternative transportation investments in addressing stated
goals and objectives. An MIS typically produces a ranking of proposed alternatives
based on relative performance and cost.
|
|
A section or operating component of a transportation project that essentially
can function independently of the remainder of the project, such as the initial
section of a planned regional rail transit system.
|
|
Designated traffic lanes that utilize a variety of traffic management strategies
such as metering, pricing, or access control to more efficiently utilize existing
capacity.
|
|
Moving Ahead for Progress in the 21st Century, the
surface transportation authorization bill for 2013-2014, passed by Congress in
July 2012 to replace SAFETEA-LU, with am emphasis on
improving transportation investment decisionmaking through performance-based
planning and programming.
|
|
[1] The change in total cost (see average cost).
[2] In travel forecasting, cost is usually taken as
either travel time or generalized cost for network links or O-D pairs.
In trip assignment, equilibrating marginal costs of
link performance functions leads to a
system optimal result.
|
|
In a utility function, MRS is the ratio at which one choice alternative
substitutes for another along an indifference curve, equal
to the ratio of marginal utilities. Under a budget constraint, MRS equals
the ratio of unit prices.
|
|
A price or other condition where demand equals supply.
|
|
A group of users of a transportation system that share common travel or
socio-economic attributes.
|
|
The proportion of trips captured by a particular mode, such as bus transit
capturing two percent of the total trips in a region.
|
|
A stochastic process having the Markov Property where the future probability
distribution is conditional on only the current state and not on the path of
past states (a "memoryless" random process).
|
|
The general case of a linear program where a general
objective function is optimized subject to linear or
non-linear, equality or inequality, and/or non-negativity constraints.
|
|
Maximum likelihood estimation (MLE) finds a model's parameters that will
generate the observed choices with the greatest likelihood.
More general than least squares estimation, MLE is used to
estimate discrete choice models.
|
|
The Center for Microcomputers in Transportation established by FHWA
in 1986 for the distribution and support of software for transportation applications
[ web ].
|
|
The average speed of vehicles traveling unimpeded on a defined section of roadway.
|
|
The difference between a true value and an observed or reported survey value
due to factors such as the survey instrument, the observer, or other elements
of the data collection process.
|
|
The four general metrics for measuring variables: nominal,
ordinal, interval, and
ratio. The measurement scale determines the type of
mathematical operations that are possible (e.g., for central tendency, nominal
scales can use only mode, ordinal scales can use mode and median, and interval
scales can use mode, median, and mean). The distinction may often be subjective
regarding these scales, depending on what the variable is actually measuring
(e.g., increasing the number of cars in a household from 1 to 2 and from 2 to 3
represents the same numerical increase in the number of cars but not necessarily
a similar increase in the level of mobility provided).
|
|
A land use model software package developed by Echenique & Partners (1987),
based on a spatial input-output framework. Similar packages include
MUSSA, PECAS,
TRANUS, UrbanSim, and
ITLUP.
|
|
A model defined between conventional macroscopic and
microscopic models, blending attributes of each. For
example, in traffic simulation a mesoscopic model might represent
individual vehicles but define movement in platoons
(for example, see DYNASMART).
|
|
A non-toxic greenhouse gas, but not a
criteria pollutant, methane is the main component of
natural gas (perhaps the most abundant fuel on earth), a contributor to degradation
of the ozone layer, and a significantly more potent GHG than
carbon dioxide (CO2).
|
|
An iterative assignment algorithm, MSA solves for optimal
link flows through the iterative application of an elementary
loading algorithm (e.g., Dial's for SUE
or AON for UE). At each iteration, link
volumes are averaged with the loading results of all previous iterations, and
are used to determine link travel times for the next iteration. MSA, a feasible
direction method with a predetermined move size, converges non-monotonically.
SUE can not use Frank-Wolfe and thus uses
MSA. In the four step model, MSA is used in
feedback to trip distribution to achieve
system convergence.
|
|
Core areas of substantial centralized population and the adjacent economically
and socially integrated areas (see census areas and
metropolitan classification).
|
|
The standard urban/suburban/rural trichotomy expanded to include the hierarchy
of urban, suburban,
exurban, and rural, terms such as
edge cities and conurbation, and
various geographic scales at which travel forecasting is
performed, including local, metropolitan,
regional, and statewide. Note that these
classification terms are often both subjective and relative with no fixed definition.
|
|
The MPO is the local or regional agency designated by the state to coordinate
federal transportation planning requirements, including
growth management and air quality.
|
|
METROSIM is an urban land use simulation model developed by Anas (1998)
that employs discrete choice models and market-clearing mechanisms for
residential and commercial land use, emploment, and transportation flows.
|
|
Maximum Entropy Matrix Estimation, a technique for
updating OD trip tables based on
maximum entropy principles and using observed
traffic counts.
|
|
A model that describes system operations in terms of individual system elements
(such as individual vehicles in traffic microsimulation models or individual
persons in activity microsimulation models)
(see Macroscopic Model; see also disaggregate).
|
|
A microscopic simulation focusing on the
behavior of individual system elements, such as individual persons or vehicles.
|
|
The time period between the end of the AM-peak and the
start of the PM-peak period.
|
|
The relocation of population from one region to another that, together with
birth and death rates, are the determinants of population change.
|
|
A path is a sequence of nodes and links in a network.
A minimum path is the optimal (shortest) path,
measured by travel time, distance, or generalized cost from a defined origin
to a defined destination. In travel forecasting, algorithms
(such as Dijkstra's)
find the minimum path tree and are used to generate travel time
matrices for trip distribution models and as an integral part of
trip assignment models.
|
|
A tree is the set of minimum paths from a specified origin
to all destinations.
|
|
A sectoring method used in economic base analysis to estimate
the proportion of basic employment by economic sector, assuming
that local demands are met by a level of economic activity equivalent to the minimum
of comparable, reference economies, with remaining activity being basic.
|
|
A software package for travel forecasting and transportation network analysis.
Developed by Comsis based on the original UTPS and now supported by Citilabs
[ web ].
Other travel forecasting packages include Cube,
EMME/2, QRSII, T-Model,
Tranplan, and TransCAD.
|
|
Major Investment Study, see MIS.
|
|
Management Information System for Transportation,
an ITS system that integrates communications, data and video
systems, incident detection, and traffic control devices in a comprehensive
transportation management system
[ web ]
|
|
To reduce the impact of a proposed project by developing counter-measures to
restore the impacted area to prior or otherwise acceptable conditions.
Perhaps most commonly linked with traffic impact studies
where the traffic impacts of a proposed development are estimated and a plan
to ameliorate the impacts is proposed and funded by the developer, evaluated
by the appropriate govenment agency, and implemented as part of the project.
Some jurisdictions charge impact fees which may fund
a portion of future network improvements based on the TIS.
|
|
Specific design commitments made as part of a traffic impact study
or environmental impact study that serve to reduce the impacts of
a proposed project. These measures may include planning and development commitments,
environmental measures, and/or right-of-way improvements.
|
|
A microscopic traffic simulation software developed at MIT
[ web ].
|
|
Traffic flow characterized by or facilities defined for utilization by single and
multiple occupant automobiles, trucks, buses, and motorcycles sharing traffic lanes.
|
|
Relaxes standard logit by allowing respondents individual
inter-related deterministic and random utility components for each choice
alternative (e.g., utility function coefficients can vary over respondents).
Mixed logit can approximate any other choice model.
|
|
A land use classification characterized by a variety of compatible land uses,
such as a mix of residential, commercial, and public land uses found in
historical downtowns and some New Urbanist development.
|
|
EPA's software package for calculating motor vehicle emissions. Mobile 6.2 is
the current version (see MOVES EMFAC)
[ web ].
|
|
Mobile sources are non-fixed sources of pollution including on-road vehicles such as
cars, trucks, and buses, and off-road sources such as trains, planes, and construction
equipment. Mobile source pollutants include NAAQS criteria
pollutants such as carbon monoxide (CO), hydrocarbons (HC),
nitrogen oxides (NOx), and particulate matter (PM)
(see stationary source).
|
|
Mobility is a measure of the degree to which the demand for personal travel
is achieved, measured by a variety of system performance indicators (see also
accessibility).
|
|
A means of conveyance between origins and destinations, modes are motorized (cars
and other private vehicles, buses, rail transit) and non-motorized (walking, bikes).
In the US, about 90 percent of all travel is by private vehicles, with the remainder
by other modes (percentage varies over activity and transportation characteristics
and over geographic areas).
|
|
Mode Choice (MC) is the third step in the conventional
four step model of travel forecasting. MC is the process by which
a traveler chooses a transportation mode for a trip, given the trip's purpose, origin,
and destination (the results of the first two steps of the four step model);
characteristics of the traveler; and characteristics of the modes available to the
traveler. Mode choice typically follows trip distribution in the
four step model sequence. Historical use of aggregate mode choice has given way to
the multinomial logit as the preferred mode choice formulation.
|
|
The market share of trips by each of the transport modes serving an area. The
historical application of aggregate mode share models was often referred to
as "modal split".
|
|
An analytical, typically mathematical, abstraction of reality used in
transportation as a tool to describe, predict, or optimize travel and
activities, land use and economic activity, traffic flow and performance,
and associated environmental impacts. A model of a transportation system
comprises a set of rules that relates defined inputs to outputs.
|
|
The process of defining model structure, functional form, variables, and parameters
(see estimation, calibration,
validation, and application).
|
|
A bias associated with arbitrary spatial zoning systems
where the associated data may be artifacts of the zoning delineation rather
than the underlying spatial behavior of the population.
|
|
A Measure of Effectiveness is a variable that is designed
to assess system performance. Also know as a
Performance Measure.
|
|
The traditional model used to analyze the spatial structure of cities and
characterized by continuously declining density gradients
from a central population and employment core. This simplified structure
facilitates presentation, analysis, and underestanding of urban theory.
Compare with polycentric model.
|
|
A simulation method that use random numbers rather
than deterministic algorithms to model complex system behavior.
|
|
An efficient algorithm to find the minimum path tree for a given origin based
on the iterative updating of alternative paths to network nodes. Alternate
algorithms (e.g., Dijkstra's) differ primarily in the sequence
that nodes are evaluated for inclusion on the minimum path.
Moore's is a label-correcting path algorithm.
|
|
In Entropy Maximization, the solution to maximizing the
combinatorial objective function subject to appropriate constraints is a trip
matrix that is the most probable distribution that could have given
rise to the observed constraints.
|
|
Transportation modes that are powered by motors, either
ICE or electric, such as automobiles, trucks, and most
forms of public transit.
|
|
Memorandum Of Understanding: a document defining
the general responsibilities of two or more entities to achieve defined
goals and objectives.
|
|
EPA's MOtor Vehicle Emission
Simulator to estimate mobile source emissions for state implementation
plans and transportation conformity analyses
[ web ].
|
|
Metropolitan Planning Organization (see MPO).
|
|
[1] Metropolitan Statistical Area
(see census areas).
[2] Method of Successive Averages (see MSA).
|
|
Network assignment that provides for the loading of multiple
user classes, which can have differential access to portions of the network (e.g.,
HOV lanes), different link performance functions,
and separate trip tables.
|
|
Transportation planning or operations that involve more than one
mode of transportation. Sometimes taken as a coordinated
planning focus on two or more modes of transportation.
See also intermodal.
|
|
A logit model for choice among more than two alternatives
(referred to as "binary logit" when the choice is between only two alternatives).
|
|
A trip assignment process that utilizes stochastic loading,
resulting in O-D flows being assigned to multiple paths
(rather than the shortest path as in deterministic assignment).
|
|
MCA is a statistical modification of category analysis used
in trip generation. When an insufficient number of data points
exist to compute reliable trip rates for all categories, MCA utilizes row, column,
and overall means to estimate rates for all cells.
|
|
A descriptive model of urban development developed by Harris and Ullman (1945)
that retains the central business district (CBD) as well as
other elements of the Concentric Ring and
Sector models but reflects non-CBD activity centers
serving as additional centers of evolving urban patterns.
|
|
Defined indices that measure the direct and indirect economic effects of
employment and income changes by sector of the economy.
|
|
A microeconomic land use model software package developed by Martinez (1996)
that represents the equilibrium behavior of land use supply and demand. Similar
packages include MEPLAN, PECAS,
TRANUS, UrbanSim, and
ITLUP [ web ].
|
|
FHWA's Manual of Uniform Traffic
Control Devices defines standards for the installation of
traffic signals and signs, pavement markings, and other traffic control
devices [ web ].
|
|
| N | [ back to top ] |
|
|
National Ambient Air Quality Standards are
the Federal standards that set allowable concentrations and exposure limits for
criteria pollutants, including ozone,
carbon monoxide, nitrogen oxides,
sulfur oxides, particulate matter, and lead.
Developed by the EPA under CAA.
See current standards [ web ].
|
|
North American Free Trade Agreement
(see NAFTA).
|
|
North American Industry Classification System,
the North American industry clasification taxonomy that replaces the
Standard Industrial Classification (SIC)
[ web ]
|
|
An aggregation technique that uses a group's average
values for variables in a disaggregate model. Valid
for linear models, but introduces aggregation bias in non-linear models
(see sample enumeration).
|
|
National Association of Regional Councils,
a national public interest organization established as an advocate for
Councils of Government (COGs) and Metropolitan Planning
Organizations (MPOs) [ web ].
|
|
In game theory, a Nash equilibrium (after Nobel laureate John Nash) exists
when no player can unilaterally benefit by changing strategy. Equivalent to
UE trip assignment.
|
|
The National Highway Institute is part of the
FHWA that provides transportation-related training
[ web ].
|
|
Approximately 160,000 miles of roads deemed critical to the economy, defense,
and mobility, including the Interstate system.
|
|
A common framework for planning and integrating ITS
interoperability, defining the system functions, physical components, and
corresponding information flows. The architecture is maintained by
USDoT [ web: NITSA;
Version 6.1 ].
|
|
A BTS product comprising a set of domestic geographic databases of
transportation facilities, transportation networks, and associated infrastructure
[ NTAD 2012 ].
|
|
Although anthropogenic sources of pollution are significant,
about half of all air pollutants are from natural sources, including soils
and plants, forest fires and volcanic activity, and decomposition of organic matter.
Natural sources are dispersed, thus their concentration in metropolitan areas is
often minimal.
|
|
National Bureau of Economic Research land use
model was developed by Ingram (1972) to simulate housing markets and policies.
|
|
National Cooperative Highway Research Program,
sponsored by the Transportation Research Board (TRB), supports
applied research that develop near-term, practical solutions to problems facing
transportation agencies
[ web ].
|
|
TRB's NCHRP Report 187 Quick-Response Urban Travel
Estimation Techniques and Transferable Parameters (1978) documented
"transferable parameters, factors, and manual techniques for simplified
travel forecasting". See NCHRP 365.
|
|
TRB's NCHRP Report 365 Travel Estimation Techniques
for Urban Planning (1998) updated NCHRP 187.
|
|
A lead agency's determination that a proposed action will not result in any
significant adverse environmental impacts, ending the environmental review process.
A positive declaration states that the proposed action is likely to have a significant
adverse impact and that an environmental impact study (EIS) will
be required.
|
|
[1] In gravity models, a variety of function forms have been utilized
for travel impedance in trip distribution,
including inverse power, negative exponential, and
combined (gamma) functions, as well as the conventional
friction factors. The negative exponential function
results directly from the standard entropy maximization
derivation: f(tij) = exp(-μtij)
[2] In traffic flow theory, the distribution of headways is
negative exponential with the corresponding arrivals Poisson distributed.
[3] In the monocentric land use model, the population density
gradient is theorized as a negative exponential distribution.
|
|
A neighborhood design philosophy derived from traditional community characteristics
such as mixed land uses in relatively close proximity. It's also known as Traditional
Neighborhood Development. Often used interchangeably with New Urbanism
and Transit-Oriented Development, Neo-traditional Design is
more correctly an architectural design philosophy.
|
|
National Electrical Manufacturers Association.
The Transportation Management Systems and Associated Control Devices Section
develops technical standards and guidelines for vehicular transportation
systems and related elements
[ web ]
|
|
NEMA's functional standard traffic controller. Controller
operations are based on the standard single- or dual-ring phase diagrams.
|
|
The National Environmental Policy Act (1969)
established national policy requiring projects using Federal funds to examine
the environmental impacts of the proposed and alternative projects prior to
Federal approval or support (see also EIS).
|
|
Hierarchical formulation of the multinomial logit model.
When some choice alternatives are correlted with others (e.g., transit modes
are more similar to each other than to private vehicle modes), the error term
independence assumption is violated. Nested logit involves the grouping
of similar alternatives into one or more "lower level" logit models, with the
"higher level" choice between the "nests" of similar alternatives.
|
|
In project appraisal, the discounting
of all current and future benefits and costs, to be incurred over the project
lifetime, to a net current value.
|
|
UTCS-1, the arterial network simulation model developed in the
1970s, evolved into NETSIM that, together with FRESIM
(freeway simulation), formed the integrated software suite TRAF
(now TSIS/CORSIM).
|
|
A graphical and/or mathematical representation of a region's transportation
infrastructure and services, comprising links and
nodes and their corresponding characteristics. Also
refers to the actual networks of highways, transit, and other modes.
|
|
The process of developing the transportation networks for a travel forecasting
model. Today, coding is most likely enhancing networks from existing models or
developing networks from aerial photographs or remote surveillance technology.
The level of detail for which network characteristics such as
links and nodes will be included
varies based on the scale and scope of the model and the policies to be tested.
A rule of thumb is to include a functional classification
level one lower than the level at which policy decisions will be made.
|
|
A broad class of OR problems that addresses network topology and/or
characteristics of network components (e.g., links and nodes) to achieve some specified
objective. A common application is the addition of capacity to a network (via added
links, lanes, or services) while minimizing total cost or maximizing user benefit.
Related to Minimum Spanning Tree and
Facility Location problems.
|
|
A system state where fixed O-D demand and network performance
are in equilibrium. In the four step model,
this is achieved in equilibrium trip assignment. Network flow is
in equilibrium when no traveler can unilaterally change route and be better off,
thus there is no incentive to change. See system equilibrium.
|
|
A streamlined version of the Simplex algorithm to solve
network minimum cost flow problems. As with transportation
simplex, the algorithm exploits the special structure of network problems.
|
|
A family of computational models based on an analogy to biological neural
networks and used to model complex non-linear systems. The basic structure
comprises: an input layer, an output layer, and one or more hidden layers,
with each layer comprising two or more neurons, and links between any or
all neurons in adjacent layers. Learning is the process of calibrating link
weights to optimize a defined cost function.
|
|
A federal program to provide discretionary support for capital funding of
new fixed guideway transit systems or extensions, based on projected system
performance and the level of local commitment.
|
|
An urban design philosophy derived from traditional community characteristics
such as grid street layouts, higher densities, and mixed land uses that increase
the relative accessibility of non-automotive modes of travel. By reducing automobile
travel and land consumption, New Urbanism seeks to minimize impacts on the built
and natural environments. Transit-oriented development and
neo-traditional design are often components of New Urbanism
development strategies.
|
|
Non-Government Organization (see NGO).
|
|
FHWA's Next Generation Simulation Program
[ web ].
|
|
Non-Home-Based -- a classification for trips which neither begin
nor end at a trip maker's residence (home). The origin of a NHB
trip is also the production; the destination
of a NHB trip is also the attraction.
|
|
National Household Travel Survey is a comprehensive
survey of household travel behavior in the US. The sample is drawn from urban,
suburban, and rural areas and is expanded to provide national estimates of
household and travel characteristics.
NHTS combines the prior NPTS and a long distance travel survey.
|
|
Oxides of nitrogen are criteria pollutants produced from
atmospheric nitrogen and oxygen when combustion occurs at high temperatures.
NOx are major air pollutants, components of acid rain and smog, and
a precursor of ozone.
|
|
In alternatives analysis, the No Build Alternative represents
the option of no additional transportation improvements beyond what has already
been planned and programmed prior to the current study. Serves as a baseline for
comparison of various alternatives to improve or expand infrastructure and services
or to manage demand.
|
|
A point joining two or more links in a transportation network,
and having attributes such as turn penalties and turn
prohibitions in addition to spatial coordinates.
|
|
An attribute of a node on a transportation network providing the cumulative
travel time from a specified origin on a minimum path tree.
|
|
A matrix of network topology containing N (nodes) rows and M (links) columns with each column
containing a single -1 and a single +1 corresponding to the start- and end-nodes of the link
in question, with all other cells equal to zero. This is also the A-matrix of constraint
coefficients in the mathematical program for the Transshipment Problem.
(see: incidence matrix ).
|
|
A scale used to measure a variable whose values are simply names and no
meaning is implied relative to rank order or intervals (also called
categorical variables).
Examples in travel forecasting include gender and occupation.
See measurement scales.
|
|
NOT meeting NAAQS standards for criteria air pollutants
(including ozone, carbon monoxide,
particulate matter, and nitrous oxides
[ web ].
|
|
An EPA-designated area whose air quality does not meet one or more
NAAQS standards.
|
|
See service employment (compare with basic
employment).
|
|
Whereas compensatory models are characterized by the
simultaneous evaluation of choice attributes so a greater value on one attribute
can compensate for a lesser value on another, non-compensatory models
choice structures (including hierarchical, sequential, and lexicographic) are
such that alternatives with attributes not meeting a threshold are eliminated
from further consideration.
|
|
A formal group, independent of any level of government, created for operational
or advocacy support of particular policy issues.
|
|
A classification for trips which neither begin nor end at a trip maker's residence (home).
The origin of a NHB trip is also the production;
the destination of a NHB trip is also the attraction
(see HB).
|
|
In multi-objective evaluation, an alternative that ranks higher on at least
one but not all attributes so that a dominant solution can not be idenfified.
|
|
Transportation modes that are not powered by motors, either
ICE or electric, including bicycles and walking.
|
|
In statistical modeling, nonparametric indicates that the number and
nature of model parameters are not fixed in advance (distribution free).
|
|
A trip assignment algorithm where the proportion of OD
flow loaded on a link depends on link flows (e.g., equilibrium assignment
algorithms explicitly reflecting congestion). See Proportional Assignment.
|
|
Congestion resulting from independent occurances of
atypical events such as incidents, special events, or weather.
|
|
To scale a vector of data to match some known or desired value:
[1] In trip generation, trip productions
and attractions, independently estimated, are scaled so that
total attractions are balanced with total productions.
[2] In statistics, a variable is said to be normalized when it is
scaled to have a mean of zero and a variance of one.
|
|
NAFTA is the 1994 agreement between the United States, Canada, and Mexico
that addresses tariffs and regulatory barriers of trade.
|
|
Oxides of nitrogen are criteria pollutants produced from
atmospheric nitrogen and oxygen when combustion occurs at high temperatures.
NOx are major air pollutants, components of acid rain and smog, and
a precursor of ozone.
|
|
National Personal Transportation Survey was a
comprehensive survey of household travel behavior conducted approximately
every seven years from 1969 to 1995. NPTS was replaced in 2001 by
NHTS and a long distance travel survey.
|
|
National Transportation Atlas Database
(see NTAD ).
|
|
National Transportation Communications for ITS
Protocol is the family of standards providing the communication protocols
and vocabulary necessary for the interoperability of electronic traffic control
equipment [ web ].
|
|
| O | [ back to top ] |
|
|
See Big O Notation.
|
|
The first stage of the transportation planning process is
Problem Definition, which incorporates Goals, broad
statements based on community values and the current environment, and
Objectives, restatements of goals in specific and measurable terms.
Problems may be defined when objectives are not met by the current environment.
|
|
A mathematical function of decision variables that is to be optimized,
often subject to specified constraints.
|
|
A modeling approach featuring data structures that allocate objects to
hierarchical classes, that allow them to inherit characteristics of higher levels.
|
|
[1] loop occupancy is the proportion of a
counting interval (typically 30 seconds)
during which a vehicle is detected by a sensor;
[2] vehicle occupancy is the number of persons per vehicle.
|
|
The Orange County Transportation Authority
[ web ].
|
|
An origin / destination pair.
|
|
The inverse of traffic assignment, where a network and
observed traffic counts are used to estimate or update
a trip table that most likely produced the counts (note
that counts alone are insufficient to infer a trip table).
|
|
A trip table in origin /
destination format (see PA Matrix).
|
|
A period of relatively low traffic volume and density (see peak).
Applications of travel forecasting increasing develop two separate
off-peak models corresponding to midday (from the
AM peak to the PM peak) and evening
(from the PM to the AM peak) periods.
|
|
Ordinary Least Squares
(see regression analysis).
|
|
Optimized Policies for Adaptive Control, a comprehensive
traffic signal control algorithm that provides both distributed intersection control
and network coordinated control (see RT-TRACS).
|
|
A control system without feedback of measured output to adjust a control
strategy. In a fixed-timed control system, a control
strategy is implemented via field controllers with no feedback of system
performance data. The advantage of open loop control is speed and
simplicity of operation (compare with Closed Loop System).
|
|
Recurring costs of operating and maintaining infrastructure and service over a
given period. Compare with capital costs.
|
|
All activity performed to ensure the effective functioning of a transportation
system, including: data collection, archiving, and processing; analysis,
modeling, and simulation; control of system components and traffic flows;
incident management; and coordination within the operations agency and with
other institutions and jurisdictions.
|
|
The application of mathematical methods and models to analysis, optimization, and
decision-making for complex real-world systems. The term Management Science is often
used synonymously with OR, and OR techniques are common tools in civil,
environmental, industrial, and systems engineering. In transportation, application
areas include Facility Location, Minimum Path,
Minimum Spanning Tree, Network Design, and
Vehicle Routing problems.
|
|
The economic value that is foregone when an alternative course of action is taken.
|
|
A solution that is deemed best based on pre-specified criteria.
|
|
Methodology to solve for the optimal levels of control variables over a defined
time interval. The control variables describe system state variables via a set
of differential equations.
|
|
Operations Research (see OR).
|
|
A type of probit analysis where the dependent variable is
ordinal, providing estimates of the explanatory variables
and the cut-points that defined the ordinal categories (logit
counterpart is ordered logit).
|
|
A scale used to measure a variable whose values are in terms of rank order (e.g.,
1st, 2nd, ...) with no meaning associated with the size of the interval between
values. Examples in travel forecasting include
attitudinal variables.
See measurement scales.
|
|
The location or zone where a trip begins (also used for
the trip itself: a zone is a origin for N trip origins). The
destination is where a trip ends.
Compare with production and attraction.
|
|
An efficient alternative to Frank-Wolfe (link-based) and
path-based assignment algorithms to solve the
UE trip assignment problem, defining
decision variables as origin-based approach proportions for each link into
a node and providing a direct conversion to route proportions and associated
convergence measures.
|
|
A survey of trip origins and destinations (and usually purpose,
time of day, and selected demographic data). Household travel surveys
utilize travel/activity diaries to gather this data. Many O-D surveys
are corridor-based and conducted as intercept surveys at key
network locations (e.g., on and off ramps on a freeway corridor to obtain freeway O-Ds).
|
|
The portion of a trip that involves accessing, waiting for, transferring to, and/or
egressing from a vehicle, as opposed to the in-vehicle portion.
Disutilities are in general higher for out-of-vehicle time.
|
|
The O3 form of oxygen, a regulated criteria pollutant.
In the troposphere, O3 is produced photochemically from hydrocarbons,
oxides of nitrogen, and sunlight, and becomes a major component of
smog; in the stratosphere, ozone protects the earth from ultraviolet
radiation.
|
|
| P | [ back to top ] |
|
|
Public-Private Partnership (aka PPP).
|
|
A trip table in production /
attraction format (see OD Matrix).
|
|
Data from a sample for which repeated measurements are made.
|
|
A survey for which repeated measurements are made of the same
respondents(e.g., a travel survey of the same households at a regular interval).
|
|
A body of theory, concepts, assumptions, and empirical evidence that
constitute a formal framework for analyzing some phenomena of interest.
|
|
A hybrid traffic network simulation model integrating components of the
mesoscopic Dynasmart [1] model with the microscopic
Paramics model.
|
|
In transportation analysis, most likely an unexpected rather than an impossible
outcome (e.g., Braess' Paradox).
|
|
The concurrent use of two or more processors (CPUs) by a single program application.
Problems and algorithms that lend themselves to parallelization can realize
faster execution times (in multi-tasking where a single CPU performs multiple
operations).
|
|
A constant describing a population property utilized in a model development
process. Often used interchangeably but incorrectly with
estimator, a calibrated value for a parameter.
|
|
A comprehensive traffic microsimulation software package
that features Application Programming Interfaces (APIs).
Developed by Quadstone [ web ].
Other traffic microsimulation packages include AIMSUN,
CORSIM, Cube Dynasim,
SimTraffic, TransModeler,
and VISSIM.
|
|
[1] Alternate forms of conventional transit operations,
designed for specific market segments and not restricted by vehicle type,
fixed routes, or fixed schedules. Includes jitneys,
taxis, demand-responsive transit, and other specialized
transit modes.
[2] Demand responsive transit such as door-to-door bus, van,
and taxi services used for special markets such as elderly and disabled riders.
|
|
A legally-defined, single ownership, single land, use contiguous area of land,
parcels form the basic disaggregate land use unit.
|
|
In multiobjective optimization and decision-making, a solution is Pareto
Optimal if no alternative improves at least one objective without reducing
the value of another objective.
|
|
Same as Pareto Optimal.
|
|
Estimation of the demand for parking spaces based on land use and time of day.
The ITE Parking Generation report is the parking
demand equivalent of ITE's Trip Generation.
|
|
Strategies to increase the efficiency of current parking supply, including
pricing, use restrictions, and preferential parking for carpools.
|
|
Regulated criteria pollutants associated with adverse health
effects and reduction in visibility, PMs consist primarily of dust from roads,
agriculture, and construction and not significantly from motor vehicle emissions.
[1] PM2.5 includes "fine particles" of less than 2.5 micrometers found in
smoke and haze, which can also be formed from chemical reactions in the air;
[2] PM10 includes "inhalable coarse particles" of 10 micrometers or less.
|
|
In traffic impact analysis, pass-by trips are
diverted to the site from traffic already utilizing adjacent streets.
These trips are part of the trip ends estimated for the site, but they do
not increase the traffic volume on the adjacent street other than via the
turning movements entering and exiting the site
(see also internal capture).
|
|
One passenger transported one mile.
|
|
The Progression Analysis and Signal System
Evaluation Routine is a traffic signal optimizer that maximizes
2-way arterial progression (bandwidth) and minimizes
signal delay, computing equlvalent fixed-time phasing, cycle length, and offsets.
(see PASSER III and PASSER IV)
|
|
A diamond interchange signal optimization program
(see PASSER II and PASSER IV)
|
|
Maximum bandwidth optimization for a traffic signal network
(see PASSER II and PASSER III)
|
|
Partners for Advanced Transit and Highways,
the University of California's Caltrans-sponsored
research center for intelligent transportation systems
[ web ].
|
|
A sequence of links and nodes connecting an origin to a destination in a
network. Used interchangably with route.
|
|
The state-of-the-practice in trip assignment is
link-based assignment, using algorithms such as Frank-Wolfe
or MSA to find the UE solution that is
unique in link flows but not in path flows. Path-based algorithms such
as gradient projection identify and store utilized paths
at each iteration and produce path-based flows.
|
|
The prior identification of paths in a network. Traffic networks typically have
a large number of paths so algorithms that either obviate path enumeration or
generate paths automatically (see column generation) are
preferred.
|
|
The structural design of roadway pavements, including thickness and
load-carrying capacity, material composition, and drainage design.
|
|
A integrated process and/or database that records, analyzes, and evaluates
pavement condition for all roadway surfaces in a defined area. The information
is used in planning and programming pavement maintenance and rehabilitation.
|
|
Passenger Car Equivalent (see PCE).
|
|
The period of maximum traffic volume and density. The distribution of trip
frequency by time-of-day typically shows morning (AM peak)
and afternoon/evening peak (PM peak) periods. Travel forecasting models have
conventionally focused on problems associated with peak period flows (such as
congestion). A behavioral response to increased congestion in peak periods has
been the increase in duration of the peak period, deemed peak
spreading (see off-peak).
|
|
For a transportation facility or network, the hour of the day during which the
maximum traffic volume occurs. Often a longer "peak period" is the salient
operational period for analysis.
|
|
[1] In the planning context, PHF is the ratio of traffic volume in the peak
period to the facility's average daily traffic (also
known as "peaking factor").
[2] In the operational context, PHF is a measure of peaking within a peak
period, usually expressed as the ratio of peak hour traffic volume to four
times the traffic volume in the highest volume 15 minute period.
|
|
The lengthening of the peak period caused by earlier and later departure times
of travelers attempting to avoid increased peak period congestion by traveling
in the peak shoulders (effectively temporal sprawl).
|
|
Production Exchange and Consumption Allocation
System is a comprehensive land use model developed by
Hunt and Abraham based on the TRANUS model.
|
|
A person not utilizing a motorized or other transportation vehicle. Typically,
an individual who is walking in, across, or along a transportation right-of-way.
|
|
The process of having other agencies or parties review the structure and
performance of a travel forecasting model and make
recommendations for model improvement.
|
|
Pedestrian Environment Factor is a qualitative index of
the degree that an area is accommodating to travel by walking.
|
|
Person-Environment Fit is a measure of the degree that
an individual's activity requirements are met by the current physical and
social environments.
|
|
Caltrans' Freeway Performance Measurement System containing
real-time and historical freeway detector
data for California freeways to compute performance measures
[ web ].
|
|
A general term for the output level of service for a transportation infrastructure
element. For roadways, a performance function represents the
relationship between input variables such as free speed, capacity, and volume and
the output performance measure of speed or travel time. Performance, rather than
supply, is a more appropriate term for assessing
level-of-service for transportation facilities and, thus, for
determining system equilibrium.
|
|
California's program for public-private partnerships with
the public and private sectors jointly responsible for the providing public
infrastructure and services
[ web ].
|
|
In transportation systems analysis, a performance
function reflects characteristics of the Transportation
System that together with demand functions (which
reflect characteristics of the Activity System)
determine network flows (volumes and travel times).
A performance function relates level-of-service to
a function of characteristics of a given facility and the associated volume, or:
LOS = P( Tsys, volume )
|
|
Output measures of system effectiveness, either measured or modeled. Often
expressed in relative terms of output (usage) to input (cost). Also known
as Performance Indicators or Measures of Effectiveness (MOE).
|
|
A time and location stamp written by a roadside controller to a vehicle's
on-board memory via local, wireless communications, which can be read by
subsequent controllers to identify the vehicle's route history.
|
|
A trip production model based on a
category analysis of individuals rather than households.
|
|
One person traveling one mile. Total person-miles traveled is an indicator of
system performance measuring total mobility in a region
based on total distance traveled (see vehicle-mile).
|
|
A single trip by a single person. The output of
trip generation is measured in person-trips.
On the other hand, a vehicle-trip is a single trip by a
vehicle, regardless of the number of occupants in the vehicle. A vehicle with
three occupants on the same trip equals one vehicle-trip or three person-trips.
|
|
A set of signal indications that permit one or more
movements to proceed simultaneously (e.g., two opposing left turns comprise a
phase that ends when at least one left turn indication ends and is replaced by
a phase comprising the other left turn and the corresponding through movements
(or both through movements)).
|
|
Peak Hour Factor (see PHF).
|
|
Pivot point modeling applies a demand function to estimate changes in demand using
only current market shares and proposed performance changes.
Incremental logit is perhaps the most commonly utilized.
|
|
PLAnning for Community Energy, Economic, and
Environmental Sustainability is a planning method developed to
facilitate forecasts of energy use for alternate land use plans. Land use
assumptions are specified via a GIS interface. The distributions of households
and employment are then estimated and alternate land use plans are compared
in terms of transportation impacts such as generated VMT
and vehicle-trips. The transport
component was developed by Fehr & Peers.
[ web ]. See INDEX.
|
|
Land development permitted and planned on multiple parcels with a compatible mix
of land uses. PUD permits developers with greater flexibility in meeting density
and land use goals. This variation from fixed lot size "grid" development often
led to sprawling, automobile-dominated development patterns.
|
|
The practice and process of developing, implementing, and evaluating
formal plans, programs, and policies to provide infrastructure and
services to achieve defined goals and objectives.
|
|
Vehicles that effectively move through a traffic network, real or simulated,
as a group. Platoon dispersion refers to the spatial
separation of vehicles in a platoon that occurs as they progess downstream
from a traffic signal.
|
|
The separation of vehicles in a platoon that occurs as
they progess downstream from a traffic signal or other upstream queueing.
|
|
Regulated criteria pollutants associated with adverse health
effects and reduction in visibility, PMs consist primarily of dust from roads,
agriculture, and construction and not significantly from motor vehicle emissions.
[1] PM2.5 includes "fine particles" of less than 2.5 micrometers found in
smoke and haze, which can also be formed from chemical reactions in the air;
[2] PM10 includes "inhalable coarse particles" of 10 micrometers or less.
|
|
The time period corresponding to the highest afternoon traffic volumes.
The PM-peak hour is the highest volume hour within the PM-peak period, which
is typically defined as a 2 to 4 hour long period
(see midday, AM-peak, and
off-peak periods).
|
|
Pavement Management System (see PMS ).
|
|
Point, line, and area sources
are idealized zero-, one-, and two-dimensional locations that are sources for
various pollutants. Large, fixed facilities such as power plants, chemical
processing industries, and petroleum refineries are point sources of a range
of air pollution emissions (AKA stationary sources).
|
|
Sources of air and noise pollutants, including mobile,
stationary, area-wide, and
natural sources.
|
|
Models used to analyze the spatial structure of cities and characterized by multiple
centers of employment and population. Compare with monocentric model.
|
|
[1] The number of persons living in a zone, region, or other defined spatial
unit, often categorized by socio-economic characteristics
or housing type.
An endogenous, variable in land use models and an
exogenous variable in travel forecasting models, especially
trip generation where population is critical in most
aggregate trip production models
(household size appears for population in
disaggregate trip production models).
[2] In sampling, the population is the entire group from which a sample
is drawn and may be defined based on any desired characteristics.
|
|
In a cohort component model, a graphical depiction of cohorts defined by age
on the vertical axis and gender horizontally) yielding a pyramid-shaped
distribution for populations with consistent natural increase.
|
|
Models or procedures applied to refine or extend core model output. Applications
in travel forecasting include link speed
estimation and air quality analysis.
See pre-processor.
|
|
Public-Private Partnership (aka P3).
|
|
See signal pre-emption.
|
|
A general term for the estimation of the value of a variable of interest in an
unknown situation. Often used synonymously with forecasting,
a term that is more often used in the estimation of values at a future time
(such as for travel forecasting).
|
|
Initial technical phase of project development to determine location, feasible
alternatives, and design options, as well as all relevant constraints.
|
|
Models or procedures that preceed core model application, typically to process
data required in the core model. In travel forecasting models,
this might be to develop auto ownership models or to
estimate joint distributions of socio-economic and
demographic data for trip generation.
See post-processor.
|
|
In traffic signal control, a binary indicator that a vehicle has activated a
sensor at an intersection stopline signaling the
controller that at least one vehicle is queued for
service. Most stopline detectors (e.g., loop detectors)
provide only a presence indication and not a count.
|
|
Same as fixed-time control.
|
|
The amount charged by a provider and paid directly by a user for consuming
a good or service. Price is usually defined to include only monetary
amounts, but overall cost can also include time and
other elements.
|
|
A fundamental economic strategy to charge users for the use of a transportation
systems based on system demand. Also known as congestion
or value pricing.
|
|
The process of converting infrastructure and/or services, in whole or part,
from public sector ownership and/or operations to private sector ownership
and/or operations (see public-private partnerships).
|
|
A means of traffic data collection that obtains measurements from an instrumented
vehicle inserted in the traffic stream (see floating car).
|
|
A discrete choice model, conceptually similar to
logit, but with multivariate Normal error terms and an
arbitrary covariance matrix and thus not limited by the IID
assumption of logit. The generality of this formulation
presents a significantly greater computational burden in estimation than does
logit (compare with nested logit).
|
|
A stage in the transportation planning process that
defines gaps between the desired or expected performance of the
transportation system, based on local values,
goals and objectives, and the current or projected
level of system performance.
|
|
The location or zone responsible for a trip occurring but also
used for the produced trip itself: a zone is a production
for N trip productions). A household generates N productions that may be split
as home-based or non-home-based. Home-based
trips, by definition, have their production in the zone containing the household,
regardless of the origin and destination
of the trip. The productions for non-home-based trips must be allocated to the
NHB trip's origin zone (see reallocation model). Contrast with
attraction.
|
|
In Transportation Systems Analysis, a Production Function
finds the set of minimum cost resource input combinations for a specified output,
given current technology, and serves as an input to supply procedures
(comparable to the microeconomic production function that maximizes output for
fixed inputs).
|
|
The process of prioritizing and committing funds to transportation projects and
programs for a defined time period based on overall effectiveness and available
resources.
|
|
A trip assignment algorithm where link flows are proportional
to OD flows (e.g., free assignment
algorithms where there are no congestion effects).
|
|
California's "Highway Safety, Traffic Reduction, Air Quality, and Port Security
Bond Act of 2006" was one of a package of California legislative bond acts that
were submitted to voters and approved in November 2006. Prop 1B provides
$20 billion for transportation infrastructure, funds the Corridor Mobility
Improvement Account (CMIA), and requires Corridor System
Management Plans (CSMP) for corridors.
|
|
Productions and Attractions, a
common abbreviation for the results of trip generation.
|
|
Plans, Specifications and construction Estimates.
|
|
Project Study Report summarizes the analysis of
feasibility and preliminary costs of project alternatives.
|
|
Persistent Traffic Cookie (see PTC).
|
|
Active involvement of the general public as a stakeholder
in the planning and development of transportation projects and programs.
|
|
Private sector provision of public infrastructure, such as roadways, with
the public sector providing a long-term franchise under which private
investors would recoup their investment, such as from toll revenues
(see Performance-based Infrastructure).
|
|
Passenger transportation services available to the general public. Conventional
forms of public transit typically operate on a scheduled basis, with defined
routes, stops, and fares, and with vehicles designed to accommodate multiple
passengers (compare to paratransit).
|
|
Infrastructure that is funded, built, operated, and/or maintained by public
agencies to provide transportation and other services to meet public demands.
|
|
Planned Unit Development (see PUD).
|
|
A Public Use Microdata Area is a
Census-defined area for which PUMS
data is available.
|
|
The Public Use Microdata Sample contains
complete household records (with identifying information removed) from the
US Census for a 1-5 percent sample. This disaggregate
data can be used to synthesize population-level
household data.
|
|
| Q | [ back to top ] |
|
|
Quality Assurance / Quality Control
(see QA/QC).
|
|
Quick Response System: a software package for travel
forecasting, incorporating transferable models and parameters compiled from
NCHRP187. Extensively expanded from the original QRS
software by AJH Associates [ web ].
Other travel forecasting packages include Cube,
EMME/2, MinUTP, T-Model,
Tranplan, and TransCAD.
|
|
A linear constrained optimization program with a quadratic objective function.
In trip assignment, Frank-Wolfe is a QP
algorithm that solves a non-linear program with linear and equality constraints
(e.g., UE Assignment) via a sequence of linear approximations
(e.g., AON Assignment).
|
|
An analysis that measures the nature of the characteristics of a sample
(e.g., an average person described in qualitative terms as tall, thin, and
middle-aged). See Quantitative Analysis.
|
|
A modeling approach, also known as discrete choice modeling,
representing a decision-maker's choice among a finite set of distinct choice
alternatives (such as the choice of alternate modes among car, bus, or walk).
|
|
Quality Assurance (QA) is a formal process to ensure confidence in the
satisfactory performance of a transportation facility or service, from
planning, through design, to management, operations, and maintenance.
Quality Control (QC) represents the components of a QA process that actively
control the quality level of the facility or service in question.
|
|
A subjective, multi-objective assessment of the well-being of individuals
or populations.
|
|
A form of incremental trip assignment where all trips for a
specified origin zone are assigned to the minimum path tree with link costs
updated prior to the assignment of trips from the next origin. Quantal
Loading is fast but an equilibrium solution is not
guaranteed.
|
|
An analysis that measures the number or size of characteristics of a sample
(e.g., an average person described in quantitative terms as 6 feet tall,
weighing 180 pounds, and 50 years old).
See also Qualitative Analysis.
|
|
Software for estimating origin-destination demand using observed link traffic
counts, turning movement, and travel times
[ web ].
|
|
A line of vehicles or pedestrians waiting to be served. Queueing Theory
is the systematic analysis of queueing behavior under various assumptions. In
conventional travel forecasting, queueing is not explicitly
reflected: queues stack vertically so there is no spill-back upstream.
|
|
A compilation of transferable parameters, factors, and manual techniques for
simplified transportation planning analysis (see NCHRP 187,
NCHRP 365, and QRSII).
|
|
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|
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Application of traffic control meters on freeway on-ramps to regulate entry
volume at a set rate or as a function of upstream traffic volumes.
|
|
A disaggregate behavioral travel demand model that defines
choice among discrete alternatives by individuals seeking to maximize
utility, with utility defined as comprising a measurable
(deterministic) component and a random component.
|
|
A stochastic path consisting of a sequence of random steps, defined by direction
and step size.
|
|
A non-scalable graphic data format, with data represented as a rectangular
grid of pixels (bitmap or compressed gif or jpg format), in contrast to
vector format (comprising points, lines, and polygons).
Raster formats are used for photographic images.
|
|
A scale used to measure a variable for which the intervals between values are
defined and with an absolute zero point. Examples in travel
forecasting include zonal income or the number of trips.
See measurement scales.
|
|
Route Directness Index is an accessibility
index defined by the ratio of Euclidean (straight-line) distance to actual travel
route distance.
|
|
A web-based self-adminstered survey instrument to collect,
process, and archive geo-coded household travel/activity diaries, REACT!
is integrated with TRACER, an in-vehicle GPS tracking device with wireless
communications with the REACT! server (based on HATS and
CHASE).
|
|
Collecting and processing data as it occurs, in a simulation or real
operating environment.
|
|
Household trip production models are based on household surveys
and estimate total household trips, including non-home-based
trips. NHB trips have productions that are not generated at home and thus must
be re-allocated to the zone of production via models that are similar in
structure and composition to trip production models. An alternative approach
assumes that the distribution of non-home attractions is
correct (after balancing to total non-home productions) and equates non-home productions to non-home
attractions for each zone.
|
|
The objectives of model validation are to verify that the
model can replicate observed system performance and that the model is sensitive
to proposed changes in model variables, parameters, and constraints.
Reasonableness checks represent a battery of basic "reality checks" on
all model components, including basic transportation and
activity system inputs, model structure and parameters
(compared to legacy models or averages for comparable areas), and model
outputs (compared to observed data). Does the model "behave" in a logical and
consistent manner? Also see model sensitivity tests.
|
|
Congestion reflecting persistent conditions where volumes
repeatedly exceed capacity at a particular location and time period.
|
|
A recursive procedure calls itself, necessitating definition of a base case
(e.g., a procedure F(n) to compute the factorial (n!) would call F(n-1), which
in turn would call F(n-2), until a defined base case F(0) is reached). An
iterative procedure repeats calculations in a loop but
does not utilize self-reference. Such a procedure is typically less elegant
but often more efficient than a recursive procedure. Both imply a
cascading process where the output of one step is the input to another.
|
|
The prototypical example of the IIA property of
logit models. Given equal utilities for two mode alternatives,
car or red buses, equal logit choice probabilities result. If half of the red buses
are painted blue, the resulting logit choice probabilities will be equal for all
three modes. Nested Logit and Probit models
can be structured to address this issue.
|
|
The portion of a cycle for which signal
indications display red to prohibit a particular
movement (see also amber and
green).
|
|
A large but well-defined geographical area comprising multiple jurisdictions
with significant social and economic interactions, for which appropriate levels
of planning and development are typically coordinated
(see metropolitan classification).
|
|
The phrase regional models may be interpreted as models that are developed
by regional agencies and/or are applied at the regional level. These models reflect
regional economics and demographics that interplay at the regional level.
Land use models have typically been built at the regional level
while historically most travel forecasting models have been built
at the local level. Increasingly, local travel models have
evolved into regional-scale models, corresponding to the scale of land use models.
|
|
An interdisciplinary field addressing the analysis and modeling of spatial
phenomena at all geographic scales.
|
|
The long range consensus plan that defines a region's transportation system
and planned improvements scheduled for funding over the next 20 years, a
basic requirement to obtain state and federal funds.
|
|
State of California statutorily created agencies charged with developing the
Regional Transportation Plan and the RTIP,
primarily created in rural areas in parallel to MPOs.
|
|
A general statistical technique for exploring relationships among variables.
It is used extensively in the transportation field, in general, and for
trip attraction and automobile ownership
modeling, in particular. A curve (often linear) is fit to the relationship
between one or more explanatory variables and a
dependent variable, typically to minimize an error term
to determine the best fitting function (see also Category Analysis).
|
|
A traffic detection system that allows for a vehicle to be RE-IDentified
downstream of an initial detection and identification. This anonymous tracking
is based on matching unique electronic "signatures" generated by a vehicle passing
over non-intrusive sensors.
|
|
Reilly's (1929) Law of Retail Gravitation, an early application of
accessibility [2] concepts, specified a market area boundary
by equating the ratios of population size to the square of distance from the
boundary for a pair of competing retail centers.
|
|
Absolute change is defined as a simple difference whereas relative
change is defined as proportional to a base level. For example, in comparing
changes in mode choice, an area can show an absolute increase in transit use
but a relative decrease, if the proportional increase in total transit trips
is less than the proportional increase in total trips by all modes.
|
|
In iterative trip assignment, a convergence parameter defined
as the relative difference between the total travel time for the current solution
and the total travel time via the current minimum path.
|
|
The degree of certainty or predictability of a measure of system performance,
such as travel time, in a transportation system.
|
|
The process of and the technologies for recording and measuring terrestrial
features and activities at a distance from the surface (such as from aircraft
or satellites).
|
|
Energy obtained from replaceable or essentially inexhaustible sources such
as solar, hydro, wind, or geothermal, typically characterized by lower
environmental impacts of production and use.
|
|
A announcement from a public agency or private entity requesting potential
consultants or contractors to submit a proposal, cost estimate, and qualifications
for professional engineering, planning, and/or related services.
|
|
A household's choice of where to live, a function of neighborhood
and regional characteristics, proximity to work locations, household characteristics
(e.g., household size, income), and the distribution of housing opportunities.
|
|
A component of non-basic (service) employment characterized
by the sales of products directly to consumers, retail employment is a common
variable in trip generation models.
|
|
Travel surveys historically recorded a trip from a non-home
destination back to the traveler's home location as a return home trip.
Increased interest in trip purpose with activity-based models
has led to this trip designation being replaced with the activity that occurs
after returning home. If home is taken as a default location,
however, the return home trip does not necessarily have a designated purpose
other than returning to this default location.
|
|
The economic and other benefits that accrue from an investment.
|
|
An index of how fast system costs rise with increasing system output, equal to
the ratio of average cost to marginal cost.
If the marginal cost is less than the average costs, then there are increasing
returns to scale, also called economies of scale.
|
|
A individual's preference that is identified via observation of an actual choice
and associated choice attributes. Compare with stated preference.
|
|
One fare-paying passenger transported one mile.
|
|
One vehicle transporting one or more fare-paying passengers one mile.
|
|
Travel oriented opposite the primary direction of commuting (e.g., commuting
from the city to the suburbs).
|
|
Radio Frequency Identification Device
technologies are small devices attached to objects that transmit
identification and tracking data to a receiver.
|
|
Request for Proposal (see RFP).
|
|
A contrived measure of model goodness-of-fit for
discrete choice models estimated via
maximum likelihood, roughly analagous to
R-squared in least squares estimation,
defined as one minus the ratio of the final to initial
log likelihood [ ρ2 = 1 - L(β)/L(0) ].
|
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In a general sense, having multiple person-trips for each
vehicle-trip, via carpools, vanpools, and similar modes.
In a narrower sense, actively arranging for additional passengers in an
existing vehicle-trip, often a commute to work.
|
|
Land legally designated for use by a transportation facility(ies).
|
|
Pavements with a concrete wearing surface
(see flexible pavement).
|
|
[1] A geographic ring is spatially defined as a portion of a metropolitan
area approximated by an annulus centered on a central business district
(CBD) and associated with land uses that decrease in terms
of relative value of land as distance increased from the center
(see also sector [2]).
[2] A ring road is equivalent to a beltway, a circumferential route
around a city, CBD, or other developed area.
|
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The Research and Innovative Technology Administration
of the US Department of Transportation is dedicated to the advancement of
research and innovative technology in transportation.
|
|
Root Mean Squared Error is a goodness-of-fit measure
equal to √[Σi(esti-obsi)2/n].
|
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The rechannelization of multi-lane roadways replacing
a through lane in each direction with a single, two-way, median left turn
lane. Remaining ROW can be used for bicycle lanes,
on-street parking, or a buffer between motorized and
non-motorized traffic.
|
|
An economic concept involving direct charges for the use of roads.
Depending on the meaning of "direct", such charges may include fuel taxes,
licence and parking fees, in addition to tolls (fixed,
variable, or dynamic). Road pricing has at least two objectives: controlling
traffic volumes (and thus congestion) and revenue generation (to fund both
transportation infrastructure and services). Pricing has been increasingly
promoted as a means of travel demand management on selected, congested facilities.
|
|
A general term for transportation infrastructure designed for motor vehicle use,
including highways, arterials, and other facility types.
|
|
A macroscopic model of platoon dispersion developed
by Robertson (1969) at TRRL and incorporated in
TRANSYT, SCOOT, and other traffic
operations software packages.
|
|
Reactive Organic Gases are volatile organic compounds
(VOC) or hydrocarbons (HC) that
contribute to smog.
|
|
Return On Investment (see ROI ).
|
|
A hierarchical traffic control strategy where a control
decision (e.g., to change or extend a phase) is executed based
on current system status and conditions projected over a fixed time horizon that
is "rolled" forward to reflect the most recent control decisions, sensor data,
and projections.
|
|
A path through a network; a series of links and nodes connecting an
origin and a destination. Used interchangably with path.
|
|
Route choice is often used synonymously for trip assignment,
the fourth major step in the four step model sequence, but
it is sometimes reserved for the application of stochastic route choice models
(compared to the deterministic models used in most trip assignment).
In this context, Route Choice is based on the theory that a traveler
will choose the route that maximizes utility.
|
|
Realtime provision of location and directions using
in-vehicle systems; also occasionally associated
with the provision of transit routing and scheduling information.
|
|
See Right Of Way (ROW).
|
|
R-squared is the short name for the coefficient of determination.
It is a goodness-of-fit measure defined as the ratio
of explained to total variance in a regression model.
|
|
The Regional Transportation Improvement Program lists the
transportation projects that a region proposes for funding, compiled from priority
lists submitted by local jurisdictions and agencies. RTIP projects must be consistent
with the regional transportation plan (RTP). RTIPs are combined
with state-level projects in the State Transportation Improvement Program
(STIP).
|
|
Right Turn On Red permitted
after a full stop.
|
|
The Regional Transportation Plan (RTP), prepared by the
designated Metropolitan Planning Organization (MPO), comprises
policies, programs, and specific projects to meet long-range transportation needs.
The RTP is updated every three years and must reflect funding constraints and air
quality regulations.
|
|
Regional Transportation Planning Agency
(see RTPA).
|
|
Real-Time TRaffic Adaptive Control System
is a cooperatively-developed system for executing multiple traffic control algorithms.
|
|
A knowledge-based system utilizing a set of "if/then" rules
on which decisions are based.
|
|
Random Utility Maximization (or Model)
(see RUM).
|
|
Settled areas not part of metropolitan areas and
characterized by very low population densities
(see metropolitan classification).
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(A program that fosters) Designated walking and cycling paths that link residential
areas and neighborhood schools.
|
|
The Safe, Accountable, Flexible, and Efficient
Transportation Equity Act -- A Legacy for Users,
the federal transportation authorization enacted in 2005
continuing the series of Federal Aid Highway Acts, addressed
metropolitan and statewide planning by modifying a range of requirements to address
flexibility and efficiency of the planning process.
SAFETEA-LU was preceded by ISTEA, the Intermodal
Surface Transportation Efficiency Act of 1991, and
TEA-21, Transportation Equity Act for
the 21st Century [ web ].
|
|
An aggregation technique that averages individual
choice probabilities from a disaggregate model over
the part of the sample that made that choice. Assumes the sample used in
estimation is representative of the population
(see naive aggregation).
|
|
Self-Administered Survey Instrument
(see SASI).
|
|
The assumption due to Herbert Simon that decision-makers select a satisfactory
rather than a strictly optimal alternative from a choice set, perhaps due to
limitation in the choice alternatives considered or the complexity of the
decision process. Compare with bounded rationality and
utility maximizing approaches.
|
|
Simulation and Assignment of Traffic to Urban
Road Networks is a combined simulation and assignment model
designed to analyze travel behavior resulting from network changes
[ web ].
|
|
"Redesigning Communities to Reduce Greenhouse Gases", the 2008 California
law linking land use planning and greenhouse gas reduction
(GHG), requires MPOs to prepare a
"Sustainable Communities Strategy" (SCS) to meet GHG
targets by reducing vehicle miles traveled (VMT) or
other strategies (see AB 32)
[ web ].
|
|
The Southern California Association of Governments,
southern California's six-county MPO (all of southern
California except San Diego County) [ web ].
|
|
An algorithm's or a software's ability to continue to perform, or perform
efficiently, when the dimension of the problem increases significantly.
The ability of a digital graphic format to change scale without distorting
the original image.
|
|
South Coast Air Quality Management
District, the AQMD for southern California.
|
|
Sydney Coordinated Adaptive Traffic System) ...
|
|
Split, Cycle and Offset Optimization Technique,
an adaptive control system developed by TRL
based on the TRANSYT optimization and analysis model.
|
|
A traffic signal phase where red is displayed to all vehicle movements, allowing
pedestrians to cross in all directions, including diagonally, simultaneously. Also
known as a Barnes Dance after Henry Barnes, an early pioneer
in traffic operations and control. Can lead to greater delay for vehicular and
pedestrian traffic by eliminating overlap phasing but may be appropriate when there
are large pedestrian volumes.
|
|
A control line for which estimated and observed performance measures are aggregated
and compared for model validation or for performance assessment, a screenline
splits a study area into two parts, capturing performance measures for flows from
one part of the study area to the other. While screenline is usually defined
on a regional scale, a cutline usually refers to a local area.
With definition of spatial scale somewhat arbitrary, these terms are often used
interchangeably (see also cordon line).
|
|
Sustainable Communities Strategy (see SCS).
|
|
Transportation facilities and services fully integrated both physically and
operationally to allow users to efficiently change modes and/or service areas.
|
|
[1] An economic sector is a basic component of an economy that is
defined in terms of primary economic activity, either as a specific
industry or in fundamental terms such as extraction, manufacturing,
or services.
[2] A geographic sector is spatially defined as a wedge-shaped portion
of a metropolitan area extending radially from a central business district
(CBD) (see also ring).
|
|
A descriptive model of urban development developed by Hoyt (1939) based on a
modification of the Concentric Ring Model with sectors
defining different land uses extending radially along major
transportation corridors to capitalize on accessibility.
Compare with the Multiple Nuclei Model.
|
|
An error introduced in GPS signals to prevent non-military
receivers from obtaining highly accurate position data (deactivated in 2000).
|
|
A evolving travel survey format designed to reduce cost
and time expenditures, and to control respondent burden while increasing data
quantity and quality (e.g., CHASE). A web-based instrument
(e.g., REACT!), can be accessed by the respondent when
convenient, integrates data quality checking, and transmits recorded data to a
server at the end of each survey period.
|
|
A bias present in statistical modeling where individuals in a sample exhibit
behavior associated with a priori preferences rather than as resulting
from hypothesized explanatory variables. For example, individuals who prefer
to use transit and not car may select to live in a transit-oriented
development based on this preference, so the resulting behavior is not
determined by (but is accommodated by) characteristics of the TOD.
|
|
A traffic control system where selected signal indications are determined by
detection of vehicle or pedestrian arrivals at a sensor. When all movements
are controlled by detection, the control is fully-actuated.
|
|
The process of investigating a model's response to small, defined changes in
model variables, parameters, or constraints. A component of both model
specification and model validation,
sensitivity testing defines the ability of the model to respond to relevant
policy variables that describe the current and planned transportation and activity
systems. Ideally, sensitivity analysis should be used for all components of the
modeling process (see also reasonableness tests).
|
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A device for identifying the presence or passing of a vehicle at a specified
location, often used interchangeably with detector (see
inductive loop detector). A sensor is a transducer that converts
a signal, such as the inductance in an ILD, to a digital measure
(such as count or occupancy).
|
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A model system where the output of one component serves as the input to a
subsequent component (for example, the Four Step Model).
Compare with simultaneous model.
|
|
Non-basic employment, defined as employment directed toward serving local
demands, thus supporting population and other local employment
(see basic employment).
|
|
The implicit value associated with a resource constraint, equal to the amount
the optimal solution will increase by relaxing the constraint by one unit.
In the transportation algorithm, if the difference in
relative shadow prices between a demand and a supply location (an
opportunity cost) exceeds the transportation cost, then
the solution can be improved (see LaGrange Multiplier).
|
|
A buzzword with two distinct meanings. The original shared economy reflected
individuals sharing resources in the sense of lending items, labor, or expertise
to other individuals at no cost other than a willingness to return the favor.
This concept was adapted by technology firms to sell primarily services for
profit where the economic transaction ("sharing") is between the technology
provider, a contracted physical provider, and a customer paying for the service.
Transportation examples include Uber and Lyft,
which are only marginally different in function and the service provided from taxi
and other conventional paratransit services.
|
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A shared-lane marking used on roadway travel lanes that may be simultaneously
utilized by various modes (cars, bicycles, and other non-motorized vehicles).
The term sharrows combines the conventional terms "shared lane" and "arrow".
|
|
An economic activity analysis and prediction method that models growth as a function
of total national growth, a proportional shift due to a national sector's performance
relative to the national economy as a whole, and a differential shift due to a local
sector's performance relative to the national sector. The constant share approach
assumes that regional sectors maintain a constant share of national sector growth.
The constant shift approach compares regional sector changes to corresponding national
sector changes to determine differential growth rates.
|
|
The moving discontinuity between two roadway sections with different speed-density
characteristics, represented in continuum flow models and observed
in the field (see web).
|
|
See Minimum Path.
|
|
[1] the less congested periods before and after the congested peak periods of
travel, providing commuters the opportunity to depart earlier or later to reduce
commuting times (producing peak spreading).
[2] the portions of a roadway adjacent to the travel lanes reserved for a wide
variety of safety-related functions (including use by emergency vehicles and
non-vehicular traffic).
|
|
Standard Industrial Classification (see SIC).
|
|
SIDRA Intersection is a micro-analytical traffic software package
for the evaluation of intersection capacity and performance. Developed by
Akcelik and Associates [ web ].
|
|
The coordination of a series of traffic control signals to optimize the progression
of traffic flow along an arterial or designated route by setting signal
cycle length, phasing, and
offsets so that traffic approaching a signalized intersection
receives a green phase prior to slowing to minimize stops and delay
(AKA signal synchronization ).
|
|
An interruption in the normal operation of a traffic control signal
to immediately serve a demand on a particular movement (e.g., to allow
an emergency vehicle to pass). The control system and the vehicle must
be able to communicate to coordinate the preemption
(see signal priority).
|
|
Where signal preemption interrupts programmed
signal operations (e.g., for emergency purposes), signal priority
only alters signal timing, such as by extending the current green phase to
accommodate an approaching transit vehicle (e.g., for schedule adherence).
The control system and the vehicle must be able to communicate for
priority treatment.
|
|
Same as Traffic Signal Coordination.
|
|
The standard algorithm to solve linear programs, developed
by Dantzig (1947), which uses a standardized tableau format for the objective
function and constraints and systematically searches corner points from an
initial basic feasible solution.
|
|
An often cited, rule-of-thumb, transit fare elasticity
value of -0.33, based on data from a 20 year period (Curtin, 1968).
|
|
A traffic microsimulation software package linked to
SYNCHRO, software for traffic systems operations and analysis.
Developed by Trafficware [ web ].
Other traffic microsimulation packages include AIMSUN,
CORSIM, Cube Dynasim,
Paramics, TransModeler,
and VISSIM.
|
|
An abstraction of real behavior via a simplified, manageable process that
models that behavior. Typically computer-based and often stochastic,
simulation provides experimental results for complex real behavior.
A distinction increasingly has been made between a simulation that
is designed to replicate a system's behavior (necessarily dynamic) versus
a simulation that is designed to produce similar outputs (typically
static).
|
|
A model where all outputs are determined at the same time (for example,
most direct demand models).
Compare with sequential model.
|
|
A gravity model used for trip distribution
derived via the Most Probable Distribution (Maximum Entropy)
approach where only trip productions are constrained to match those input from trip
generation. Until recent years, such models were predominant in travel
forecasting applications (see Doubly Constrained Gravity Model).
|
|
A State Implementation Plan, required of states with areas that do
not achieve conformity with CAAA requirements,
documents the proposed regulations and process to be implemented to achieve conformity.
|
|
Access and egress points from a land development site to
the adjacent transportation network. Site access design is a key component of
traffic impact studies, influencing the directional distribution
of traffic to and from the site and thus traffic impacts and
options for mitigation.
|
|
Same as Traffic Impact Analysis.
|
|
Sketch planning is the application of simplified methods of analysis to provide
approximate performance estimates in the initial screening of alternatives. With
advances in computing, traditional sketch planning methods are of less benefit
relative to full model applications. However, for smaller area analysis, "What if?"
models that integrate GIS, databases, and graphic user interfaces
have become popular tools in public participation forums
such as charrettes.
|
|
Skimming a network is the process of systematically identifying network
paths (typically) based on the minimization of travel time,
distance, or generalized cost. The resulting matrices of zone-to-zone
impedances are called skims.
|
|
Ad hoc ridesharing combining elements of hitchhiking and carpooling to
enable SOV drivers to utilize HOV facilities
by picking up "sluggers" waiting at designated locations.
|
|
An increasing trite buzzword implying a process or technology that
facilitates transportation planning, design, or management, or increases
the efficiency of transportation operations. Similar terms include
"advanced" and "intelligent".
|
|
A credit-card-sized authentication device with an imbedded microchip containing
personal identification information that can be read via proximity or contact
with a sensor/reader. Used in car sharing systems to
provide vehicle access to only the reservation-holder during the reservation
period.
|
|
The interconnection of municipal systems (e.g., public services, energy generation
and distribution, transportation) via information and communications technologies.
Also known as the Connected City.
|
|
The evolution of the domestic power generation and distribution system that
can respond to dynamic electricity demands in real time.
|
|
A planning concept focused on increased density and diversity, circulation
continuity, alternative travel modes, and a better sense of neighborhood
scale. By reducing automobile travel, land consumption, and the need for
new transportation infrastructure, smart growth seeks
to minimize impacts on the built and natural environments. Also known as
New Urbanism, neo-traditional design,
and transit-oriented development.
|
|
A GIS sketch planning tool for comparing alternative
and use and transportation scenarios and evaluating outcomes using community
and environmental performance indicators. Developed by Criterion Planners for
USEPA in 2002
[ web ].
See also INDEX.
|
|
A version of PLACE3S from the Electric Power
Research Institute [ web ].
|
|
Standard Metropolitan Statistical Area
(see census areas).
|
|
A generic term for visibly poor air quality, smog is an historical
contraction of smoke and fog. Today's photochemical smog is
characterized by a stagnant haze produced by chemical reactions of sunlight
and various air pollutants including
nitrogen oxides and volatile organic compounds.
|
|
System Optimal (see SO).
|
|
The time interval since the end of a vehicle's last trip, a key factor in
determining engine emissions and cold starts.
|
|
A combination of socio-economic and demographic
characteristics of a population.
|
|
Another name for K Factors, calibration parameters that provide
a means for cell-by-cell adjustments in gravity models, and which
typically are related to socio-economic variables to lend credibility in forecasting.
|
|
Characteristics of the population, including income, employment status, and auto
ownership, usually defined at the household and individual levels. While often used
interchangeably with the term demographic data, socio-economic
data are perhaps best viewed as time-varying attributes that define status within a
state (such as auto ownership or income) whereas demographic data correspond to fixed
characteristics of population that define the state (such as age and gender).
Socio-economic and demographic data, together with land use data,
are key inputs to trip generation.
|
|
A distinct, non-home activity on a trip chain.
Multi-purpose activities occuring at the same location (a single stop on a trip chain)
typically have been considered as a single sojourn (although this may be a survey
limitation).
|
|
Single Occupant Vehicle (see HOV).
|
|
Oxides of sulfur are criteria pollutants produced in the
combustion of sulfur-containing fuels.
|
|
The average speed of all vehicles occupying a defined section of roadway at a
point in time (the harmonic mean speed). With volume and
density, space mean speed defines the
fundamental diagram of traffic flow.
Compare with time mean speed.
|
|
The three dimensional representation of human activity and travel developed
by Hagerstrand depicts the space that an individual can
access, in the time available and reflecting the speed of movement through
the defined space, as a prism. In idealized space, the prism is a cone
expanding radially in 2-D space as it extends vertically in time from a
fixed location, intersecting a second cone collapsing to an alternate
location in space and time that the individual is constrained to visit.
|
|
The distance (in feet) between successive vehicles traversing a section
of roadway, usually averaged over all vehicles on a defined section.
Spacing s (distance headway) is the inverse of density d:
s = 5280/d in feet/vehicle (see also headway).
|
|
Pertaining to dimensions of space such as location, distance, direction,
elevation, and area. Often used synonymously with "geographic".
|
|
Theory and models that address the interdependence between geographical areas.
Trip distribution utililizes models of spatial interaction.
|
|
The geographical separation of employment and housing, paricularly for
low income or minority groups.
|
|
A location or zone that exhibits trip rates or patterns that can not be captured
by a study area's trip generation model. Separate surveys and
models are used to estimate productions and
attractions for special generator. Examples include airports,
college campuses, and military bases.
|
|
Part of a comprehensive plan corresponding to a defined
function and/or spatial area and containing development standards and criteria
that supplement those of the comprehensive plan.
|
|
The process of defining model structure, functional form, variables, and parameters
(see estimation, calibration,
validation, and application).
|
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Speed is distance traveled per unit time (the inverse of unit travel time).
In traffic operations, two measures of average speed are
space mean speed and time mean speed. SMS is
the average speed of all vehicles occupying a defined section of roadway at a point
in time. TMS is the average speed of all vehicles passing a point on a roadway for a
defined period of time. With volume and density,
space mean speed defines the fundamental diagram of traffic flow
(which provides a direct link to performance functions). Speed and
travel time are standard performance measures in system evaluation.
|
|
A raised section of pavement across a travel lane designed to reduce vehicle speed.
Speed bumps are more pronounced than speed humps, thus, humps
have become more common on roads (see also traffic calming).
|
|
See look-up table.
|
|
A traffic stream model that depicts the relationship between
speed and density, such as
Greenshields' or Greenberg's models.
|
|
An often pejorative term referring to the expansive spatial growth of a metropolitan
region, often at lower development densities. The development of most American
suburban areas is considered sprawl.
|
|
Any individual or group that holds some intrinsic interest in and may be
impacted by a specific plan, policy, or project.
|
|
Employer groups identified by primary economic activity to standardize data
collection and analysis (see sector [1]), since replaced
by NAICS.
|
|
Part of the overall transportation planning process, the SIP is a statewide
plan mandated by the CAA and containing procedures to monitor,
control, maintain, and enforce compliance with NAAQS.
|
|
The highest level of research and development of a specific technology or concept
at the current time (see state-of-the-practice).
|
|
The level of general deployment of a specific technology or concept
at the current time (see state-of-the-art).
|
|
A geographical coordinate system based on distance from a defined origin. SPC
systems may vary by state to minimize distortion. GPS utilizes
latitude and longitude.
|
|
A individual's preference expressed in response to a set of hypothetical choices.
Compare with revealed preference.
|
|
A travel forecasting model developed for an entire state
to address statewide planning issues (such as freight
modeling) and to coordinate input to and improve consistency of
regional models, increasing common in the post-ISTEA era.
|
|
Network assignment with fixed (versus dynamic) demand
(see dynamic assignment).
|
|
Large, fixed facilities such as power plants, oil refineries, and chemical processing
industries (also known as point sources). See also
mobile sources and natural sources.
|
|
A car sharing system linked to rail transit systems
where a reserved shared-use vehicle is accessed at the end of a rail trip
using a smart card and is later returned to the station
to make the return rail trip. A balanced system has a shared-use vehicle that
is returned to the station at the end of the work day to be picked up by a
commuter returning home to use the car until the next morning
(e.g., ZEVNet).
|
|
Surface Transportation Environment and Planning
Cooperative Research Program, part of SAFETEA-LU.
|
|
The State Transportation Improvement Program combines
RTIPs and state-level projects and determines which transportation
projects will be funded. All STIP projects must be consistent with the long-range
transportation plan (LRTP). The STIP typically covers a five year
period and is updated every two years (see TIP).
|
|
A probabilistic function or process; having a random component
(see deterministic).
|
|
A network loading process that assumes a distribution of perceived travel times
and thus produces a multipath assignment (e.g.,
Dial's Algorithm). Compare to Wardrop's
Principles, both which assume perfect knowledge of all path travel times and lead
to deterministic assignments.
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|
An equilibrium trip assignment that
satisfies a stochastic version of Wardrop's 1st Principle
that states that no traveler can improve his perceived travel time by
unilaterally changing routes. An SUE is obtained using MSA
with stochastic loading (e.g., Dial's )
whereas UE typically uses Frank-Wolfe and deterministic loading
(e.g., AON ).
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[1] A designated location on a transit line where a transit
vehicle stops to allow passenger boarding and unboarding.
[2] A vehicle coming to a complete stop, due to traffic control, congestion,
of other factors, contributing to the overall delay on a trip.
|
|
A linear-in-parameters multivariate statistical technique for estimating causal
relationships. SEM, which includes regression, path analysis,
simultaneous equations, and factor analysis as special cases, is confirmatory
rather than exploratory. It combines a structural model with measurement models
for exogenous and endogenous variables
which allows for the estimation of latent variables.
|
|
Infrastructure (e.g., a bridge) characterized by deteriorated conditions and a reduction in
structural load-carrying capacity (see functionally obsolete).
|
|
A defined region within which estimates of travel demand and system performance
are desired. A corridor is a linear study area focused on
one or more transportation facilities along the corridor.
|
|
A portion of a defined study area for a regional travel
forecasting model that is selected for focused analyses, a process that often
involves extraction of a sub-area network and a sub-area
trip table.
|
|
The process of extracting a sub-area model from a larger
(typically regional) model that involves defining the spatial extent of the sub-area
and extracting a sub-area network and the corresponding sub-area
trip table. The external network and travel data is removed, with
the resulting model serving essentially as a window on the
regional model (compare with a focus model).
|
|
Characterized as predominantly residential areas adjacent to cities and usually
with significant social and economic interaction. Geographically, the part of a
metropolitan area outside of a center city
(see metropolitan classification).
|
|
The movement of population from urban areas to the development periphery (or
suburbs), classically characterized by lower density, automobile-dominated housing.
|
|
A linear-in-parameters multivariate statistical technique for estimating causal
relationships. SEM, which includes regression, path analysis,
simultaneous equations, and factor analysis as special cases, is confirmatory
rather than exploratory. It combines a structural model with measurement models
for exogenous and endogenous variables
which allows for the estimation of latent variables.
|
|
A buzzword for a typically public-funded project characterized by achievement
of one or more expected objectives within the expected budget, when similar
projects have not met objectives or have incurred cost overruns
(compare with boondoggle).
|
|
Stochastic User Equilibrium (see SUE).
|
|
Oxides of sulfur (SOx) are criteria pollutants produced
in the combustion of sulfur-containing fuels.
|
|
The degree of banking of a roadway on a curve to counter the centrifugal force
on a vehicle traversing the curve.
|
|
The physical extent of transportation system infrastructure and services provided.
Supply is often referenced as the broadly defined counterpoint of
demand, but performance is utilized
when level-of-service characteristics are relevant.
|
|
The overall, performance-based, production and distribution management of a
commodity from obtaining raw materials through intermediate and final consumption.
|
|
In Transportation Systems Analysis, the supply function
represents the relationship between transportation infrastructure and services that
a supplier (often a government agency) is willing to provide and the state of the
current system, the costs of system alternatives, and expected system behavior. In
travel forecasting, supply procedures typically are not specified analytically;
rather, they are where the analyst "breaks" and controls the overall TSA process and
evaluates alternative system options from a "what if?" approach. Supply alternatives
are typically specified exogenously, then performance and
demand functions are equilibrated to determine flows for the
specified alternative.
|
|
Travel demand that was not previously observed due to high
costs of travel but when capacity is increased or price decreased, is now observed
on improved facilities. A more common term, induced demand,
suggests that the "improvement" itself is be sufficient to increase demand rather
than demand being determined by activity and lifestyle behavior and cost factors.
Suppressed demand would not include that associated with socio-demographic growth.
|
|
The systematic collection of data representing the behavior of a defined population
(see: cross sectional, Longitudinal, or
Panel Survey;
household travel, external travel, or
origin-destination
|
|
The translation of survey data into defined categories suitable for
data processing and analysis.
|
|
The long-term stewardship of the natural and built environments, reflecting
the environmental, economic, and social dimensions of resource maintenance
and consumption.
|
|
Under SB375, California MPOs must
include a Sustainable Communities Strategy (SCS) that incorporates
regional land use and housing strategies into the Regional Transportation
Plan (RTP), with the objective of achieving targeted
reductions in Greenhouse Gas (GHG) emissions from cars
and light trucks (see also Alternative Planning Strategy).
|
|
[1] A land use pattern characterized by growth and development occurring in a
manner supported by infrastructure and financial resources, and proportional to
the preservation of the current built and natural environments.
[2] a general social, economic, and environmental perspective toward addressing
current needs without compromising future needs.
|
|
A component of sustainable development but otherwise not
consistently defined beyond transportation systems supported by sustainable
infrastructure as well as financial, natural, and other resources to meet
mobility needs. Sustainable mobility, also called "new mobility", commonly
extends the definition to more formal operational terms.
|
|
A general agent-based modeling software platform developed
by the Sante Fe Institute
[ web ].
|
|
StateWide Integrated Traffic Records System
is a database of traffic incidents maintained by the California Highway Patrol
(see also TASAS ).
|
|
A comprehensive software package for traffic systems operations and
analysis, linked to SimTraffic, a traffic
microsimulation software package.
Developed by Trafficware [ web ].
|
|
Disaggregate household level data that is synthesized from population-level
marginal demographic distributions and small-sample joint distributions.
|
|
A collection of independent but interrelated components, real or abstract,
acting in form and/or function as a integrated whole.
|
|
The comprehensive approach to defining, formulating, and solving problems
associated with complex systems, such as transportation systems, and applied
to planning, design, implementation, operations, and
management tasks.
|
|
A system state where overall demand and system performance are in
equilibrium. In travel forecasting,
this would corresponds to full equilibration of trip frequency, destination,
mode, time-of-day, and route. In the four step model, only
route choice is in equilibrium, unless system feedback
is applied. See network equilibrium.
|
|
A system optimal (SO) trip assignment satisfies
Wardrop's 2nd Principle that states, for a given
origin-destination pair, that the total travel time is a minimum. An SO
assignment is optimal but is not an equilibrium result, since individual
travelers could improve their travel times by unilaterally changing routes
(see also user equilibrium).
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| T | [ back to top ] |
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A test of variable significance in least squares and
other estimation methods, a t statistic is computed as the ratio of a
variable's estimated coefficient to the standard error of that coefficient.
If the calculated value is greater than the critical value, then the null
hypothesis that the variable's actual coefficient is
equal to zero is rejected. In binary regression, the t statistic is the square
root of the F statistic.
|
|
Technical Advisory Committee, often associated with
travel forecasting and related modeling efforts to provide
peer review during model development and application.
|
|
The Traffic Accident Surveillance and Analysis
System is a database that integrates traffic incident data from CHP's
SWITRS with a Highway Data Base maintained by
Caltrans.
|
|
Traffic Analysis Zone (see TAZ).
|
|
Transportation Control Measure (see TCM).
|
|
Transportation Development Act, California state law
(1971) that dedicates 0.25 percent on each dollar on retail sales to transit
and non-motorized transportation.
|
|
Travel Demand Management (see TDM).
|
|
The Transportation Equity Act for the 21st Century,
the federal transportation authorization enacted in 1998 and
continuing the series of Federal Aid Highway Acts, continued
the metropolitan and statewide planning requirements from ISTEA
but consolidated the broad range of factors to be considered in the planning process.
TEA-21 was preceded by ISTEA,
the Intermodal Surface Transportation Efficiency
Act of 1991 and followed by SAFETEA-LU,
the Safe, Accountable, Flexible, and Efficient
Transportation Equity Act -- A Legacy for Users
(2005) [ web ].
|
|
A standing committee organized and utilized by MPOs and
transportation authorities to provide regular review of
technical planning and modeling activities, typically comprising engineers,
planners, and similar professionals from local and state agencies.
|
|
Activities that foster the dissemination and application of a innovative
technologies and methodologies.
|
|
Replacing a commute trip by performing a work activity at home (or a
telecommuting center closer to home than the workplace is), creating
a potential trip reduction (at least in the peak commute period). A
substitution of telecommunications for travel.
|
|
The conveyance of information via electronic means, whereas transportation is the
conveyance of people or freight via physical means. Substituting telecommunications
for travel can affect trip rates and the associated system impacts.
|
|
A transportation component of the built environment that includes the
interface facilities that allow for transfers between different modes.
|
|
The excess time incurred at the origin and destination of a trip, accessing or
egressing an activity and beginning a trip's primary travel component. Terminal
time is often added to skim tree results to better reflect
full point-to-point travel time.
|
|
A Twenty-Foot Equivalent Unit container, the standard unit
of measure to quantify container traffic flows. One (8 foot by 8 foot by) 20-foot
long shipping container equals one 20-foot Equivalent Unit.
|
|
An independent provider of transportation, warehousing, and logistics
services to buyers and/or sellers.
|
|
A trip with both its origin and its
destination located outside of the study area
(see also internal trip and external trip).
|
|
Ttransportation Investment Generating Economic
Recovery (part of ARRA).
|
|
Topographically Integrated Geographic Encoding and
Referencing files are digital maps produced by the US Census Bureau.
|
|
A simulation where all variables are updated at a fixed
time increment (e.g., every second); in an event-based
simulation, variables are updated with the occurance of specified events (e.g.,
arrivals or departures for a queue).
|
|
The average amount of time an individual allocates for daily travel. Time budget
theory postulates that people with similar socio-economic and
life style characteristics tend to have similar time budgets.
Empirical evidence supports population averages over a wide range of infrastructure
and land use characteristics.
|
|
A conceptual framework for the analysis of activity and travel that reflects
the simultaneity of time and space and the constraints that define possible
actions, typically expressed in a three dimensional graphical representation
(see Hagerstrand ).
|
|
A time in motion study produces the distribution of trips from
a travel survey based on reported trip start and end times,
providing the proportion of total trips actually in motion at a specified time.
|
|
The average speed of vehicles passing a point on a road over a defined period
of time (the arithmetic mean speed). Compare with space mean speed.
|
|
In the conventional Four Step Model, Time-of-Day (TOD)
modeling can be considered a 5th step, often executed at a point prior to
trip assignment to convert generated daily trips to those
trips occurring during a particular period of analysis (such as the
peak hour).
|
|
The proportion of daily vehicle-trips occuring in a designated period, such as
a peak-hour or a peak-period. In travel forecasting, these
parameters are based on travel survey data and are used to convert daily
PA trip tables to period-specific OD
trip tables prior to assignment.
|
|
Data defined and ordered for specified (usually regularly distributed) points in
time, as well as methods and models used to describe and forecast with such data.
|
|
A plot of vehicle trajectories over time and space, with space defined along an
arterial or other roadway and time reflecting movement and queueing.
|
|
See space-time prisms.
|
|
How individuals allocate their time to activity and travel over defined
time periods.
|
|
The concept that an amount of money today can be invested and earn interest by
a future time, forming the basis of project appraisal.
|
|
Transportation Improvement Program (see TIP).
|
|
That portion of the Civil Rights Act of 1964 that ensures
environmental justice in the location of transportation
infrastructure and for improvements in system performance.
|
|
Trip Length Frequency Distribution (see TLFD ).
|
|
Traffic Management Center (see TMC ).
|
|
USDOT's Travel Model Improvement Program is designed
to foster the development and application of improved transportation modeling
methods and capabilities to meet local, state, and federal planning requirements
[ web ].
|
|
A software package for travel forecasting and transportation network analysis.
Developed by T-Model Corporation and owned by PTV
[ web1 ;
web2 ]
Other travel forecasting packages include Cube,
EMME/2, MinUTP, QRSII,
Tranplan, and TransCAD.
|
|
Traffic Operations Center, same as TMC.
|
|
[1] Time-of-Day (see TOD[1] )
[2] Transit Oriented Development (see TOD[2]).
|
|
Time-Of-Day Factor (see TODF)
|
|
A fixed or distance-based fee charged to users of certain roadways and bridges.
As federal and state revenues are declining from fuel excise taxes, increased
pressure has been placed on alternative revenue sources such as tolls, including
as part of congestion pricing where tolls can
serve to regulate demand as well as generate revenues.
|
|
A trip chain -- a sequence of trips
and activities, typically starting and ending at home.
|
|
A variation of the conventional trip-based travel forecasting model that uses
tours rather than individual trips and
thus can account for the linkages between individual trips and activities (and
thus better represent the underlying connectivity of travel behavior). Compare
with trip-based and activity-based models.
|
|
A software package for travel forecasting and transportation network analysis
that evolved from TranPlan. Marketed by Citilabs
[ web ]. Other travel forecasting
packages include Cube, EMME/2,
MinUTP, QRSII, T-Model,
and TransCAD.
|
|
An traffic simulation software suite integrating NETSIM
for arterials and FRESIM for freeways, that evolved into
TSIS/CORSIM.
|
|
The units of transportation flow, such as pedestrians or vehicles, moving along a path.
Compare with transportation and transit.
|
|
A defined zone for travel forecasting and traffic simulation
studies, represented in the network by a centroid.
See also census tract.
|
|
The process of loading vehicle traffic onto a network,
traffic assignment is often used interchangeably with trip
assignment, which more broadly defines the process of loading trips,
vehicle-trips or person-trips, to appropriately defined modal networks.
|
|
Local street design techniques that reduce traffic speeds and discourage traffic
incursion in residential neighborhoods to improve local street safety and
neighborhood quality of life. Techniques include physical traffic barriers
(e.g., diverters, chokers, speed humps),
revised street alignments (e.g., traffic circles, chicanes),
and traffic speed enforcement.
|
|
A State of California program enacted in AB 2928 (2000) that designates
funding for specific projects to address traffic congestion.
|
|
The control of traffic via any of a number of passive rules or signs (including
travel way delineations, rights-of-way and other rules-of-the-road, and traffic
markings and signs) or active human agents or control devices (police officers
and traffic signals), to optimize safe and efficient flows.
|
|
Observed volume counts on network links, often collected
annually for a 24-hour period. Detectors such as
ILDs are becoming more widely deployed to provide
continuous traffic data (see PeMS), replacing the need
for annual field studies using mechanical detectors such as pneumatic tubes.
In travel forecasting, counts are used in model
validation as well as for updating
trip tables, particularly for real time traffic management.
|
|
The Institute of Transportation Engineers (ITE) defines
Traffic Engineering as "the phase of transportation engineering
that deals with the planning, geometric design, and traffic operations of
roads, streets, and highways; their networks, terminals, abutting lands,
and relationships with other modes of transportation."
|
|
Established and experimentally verified principles that describe mathematically
the interactions between vehicles, drivers, and transportation infrastructure.
|
|
The process of completing a Traffic Impact Study.
|
|
A Traffic Impact Study (TIS) is conducted to assess the effects on
traffic flows of changes in land development. The analysis often follows the
general steps of the four step model but while regional
travel forecasting models may be used with large scale
development changes (often as part of an EIS), various
heuristic methods are often used for smaller scale land use changes. The
TIS focus is the quantification of traffic impact and the development of
mitigation measures and impact fees.
|
|
In queueing theory, the ratio of the mean arrival rate to
the mean service rate (must be less than 1.0 for most queueing relationships to
apply).
|
|
A hub for management, operations, and control of traffic networks, incorporating
real time data collection via loops, CCTV,
and other sensors; communication technologies such as
VMS and HAR; traffic analysis capabilities
such as expert systems, microsimulation,
and control optimization software, and visual display capabilities. A TMC
addresses special events, incidents, and public relations, and the day-to-day
management of traffic systems.
|
|
Optimizing the performance of an isolated traffic signal, with regard to signal
phasing and timing, or a series of
signals, with regard to phasing, timing,
and coordination.
|
|
The coordination of a series of traffic control signals to optimize the progression
of traffic flow along an arterial or designated route by setting signal
cycle length, phasing, and
offsets so that traffic approaching a signalized intersection
receives a green phase prior to slowing to minimize stops and delay
(AKA signal coordination ).
|
|
Macroscopic speed-density models that describe basic uninterrupted traffic flow,
including the Greenshields, Greenberg,
and Underwood single-regime models, and multi-regime models
such as Edie's.
|
|
Integrated software for intersection capacity analysis and traffic impact analysis.
Developed by Dowling [ web ].
|
|
A software package for travel forecasting and transportation network analysis.
Evolved into TP+.
Marketed by Citilabs [ web ].
Other travel forecasting packages include Cube,
EMME/2, MinUTP, QRSII,
T-Model, and TransCAD.
|
|
A software package for travel forecasting, incorporating an integrated
GIS. Developed by Caliper [ web ].
Other travel forecasting packages include Cube,
EMME/2, MinUTP, QRSII,
T-Model, and Tranplan.
|
|
The degree to which a model developed for a particular time and location can
be successfully applied to a different time and/or location.
|
|
A third generation travel analysis software package, incorporating microsimulation
and activity-based approaches to provide more accurate assessment of travel impacts,
especially regarding performance and air quality assessment. Developed by Los Alamos
National Laboratories ( LANL ),
a commercial version was marketed by IBM Business Consultants
[ web ] and an open-source version is
available via FHWA [ web ].
|
|
Often used synonymously with transportation, particularly
in journalism (if for no other reason because "transit" has half as many letters as
"transportation"), transit reflects the carrying of people or goods through space,
but most often refers to local conveyance, especially of people by public modes.
A transit agency thus refers to an institution that primarily addresses conveyance
of people via public modes (see public transit).
Compare with transportation and traffic.
|
|
An individual lacking alternative modes of transportation and thus dependent
on public transit to meet private mobility needs.
|
|
A defined route along which a transit
vehicle travels, usually on a defined schedule and stopping at designated
transit stops.
|
|
Residential, commercial, or mixed use developments designed to maximize access
to and usage of public transport. New urbanist or
neo-traditional development designs typically are more amenable
to transit-oriented development than are conventional urban development approaches,
but none of these design alternatives require transit to be integrated.
Transit-Oriented Developments (TODs) may be designed jointly with new transit
systems. The growth in domestic rail transit systems initially was accompanied by
expectations for joint development where TOD accessibility
benefits could be taxed to help pay for the rail project; today, however, TODs
may receive tax concessions and other financial incentives to encourage development
supportive of transit use.
|
|
The transfer of a commodity from one form of transportation
(carrier, mode, container type) to another that explicitly involves unloading and
reloading of the commodity with the goal of reducing overall transportation cost.
Compare to transshipment.
|
|
A traffic microsimulation software, linked to TransCAD.
Developed by Caliper [ web ].
Other traffic microsimulation packages include AIMSUN,
CORSIM, Cube Dynasim,
Paramics, SimTraffic,
and VISSIM.
|
|
An electronic tag attached to a vehicle and scanned by a roadside device
that identifies the vehicle and takes appropriate action (e.g., charge a
toll).
|
|
Various strategies to reduce private vehicle usage and/or improve traffic flow to
reduce vehicle emissions. Examples include ridesharing programs, freeway service
patrols, and improved transit programs.
|
|
The most general expression for all system elements relating to the process
or action of moving people or freight through space. A transportation agency
thus refers to an institution that addresses most if not all system elements
relating to the process or movement over space of people or freight.
Compare with traffic and transit.
|
|
Same as Travel Demand Management.
Programs and projects to reduce transportation demand,
including ridesharing, transit service enhancements, and parking management.
Transportation Systems Management is the corresponding
supply-side process.
|
|
The interdisciplinary development and application of economic concepts and methods
to the planning, analysis, and operation of transportation systems.
|
|
The Institute of Transportation Engineers (ITE) defines
Transportation Engineering as "the application of technology and
scientific principles to the planning, design, operation, maintenance, and
management of systems and facilities for any mode of surface transportation
in order to provide for the safe, rapid, comfortable, convenient, economical,
and environmentally compatible movement of people and goods."
|
|
A sub-discipline of geography that studies the spatial patterns of movement
of people, goods, and information.
|
|
A fee levied on a developer by a jurisdiction to
compensate for the expected transportation impacts of the development,
usually determined as part of a traffic impact study.
See impact fees.
|
|
The Transportation Improvement Program (TIP) is a plan for
state and federal funds to be allocated to local and regional transportation
projects. In California, the TIP is cooperatively prepared by local governments,
local and regional transportation agencies, and Caltrans. It covers a 5-7 year
period and is updated every 2 years. A Regional TIP lists
highway and transit projects from priority lists developed by local jurisdictions.
The state TIP is submitted to the
California Transportation Commission and incorporates elements
of the regional TIPs.
|
|
Not-for-profit organizations that coordinate and/or provide transportation services
in defined employment centers, TMAs are often public/private partnerships.
|
|
The "continuing, comprehensive, and collaborative" (3C) process
to develop and maintain a transportation system to meet needs for the effective
and efficient movement of people and goods reflecting social, economic, and
environmental constraints. The Transportation Planning Process
involves defining goals and objectives, monitoring system performance, identifying
problems, generating and analyzing alternatives, evaluating, selecting, and
implementing a preferred alternative.
|
|
A general term for models used in
transportation planning, usually implying models used for
travel forecasting but also including land use
and other models used in planning.
|
|
The Transportation Planning Process is the system-analytic application of
continuing, comprehensive, and cooperative planning. Often represented as five
broad stages of (1) problem definition,
(2) solution generation, (3) solution analysis, (4) evaluation and choice, and
(5) implementation and monitoring.
Travel forecasting occurs during the third stage, solution analysis.
|
|
A fundamental problem in operations research that seeks the
single commodity, minimum cost flow for N supply points directly connected to
each of M demand points. Optimal versus descriptive, it is directly applicable
to freight distribution problems but not to conventional travel forecasting
(see Hitchcock Transportation Algorithm).
|
|
The Transportation Research Board, a branch of the National
Academy of Science, promotes innovation and progress in transportation through
research and facilitates the sharing of information on transportation practice
and policy [ web ].
|
|
In the Manheim/Florian framework for transportation systems analysis,
the Transportation System constitutes the networks (modes,
links, nodes, etc.) connecting a region's Activity System.
The Transportation System in defined by supply functions
and is a key element in defining performance functions.
|
|
Transportation Systems Analysis (TSA) as formalized by Manheim
and later expanded by Florian (1986) is a framework for the systematic analysis and
evaluation of transportation systems. The framework is flexible to allow components
to be specified exogenously or endogenously
based on the scale and scope of the models and policies being studies. Basic components
include demand and performance procedures, as well
as activity location and supply procedures.
|
|
Programs and projects to increase performance of the
transportation system via lower cost improvements in the design, maintenance,
and operations of existing facilities rather than investing in major increases
in infrastructure. Travel Demand Management is the
corresponding demand-side process.
|
|
The movement of freight from one carrier and/or mode to another carrier and/or mode.
Compare to transloading.
|
|
An generalization of the Transportation Problem that seeks
the single-commodity, minimum cost flow for networks with intermediate
(transshipment) points. The system optimal formulation
of the trip assignment problem is a multi-commodity
transshipment problem.
|
|
The TRAffic Network StudY Tool, an optimization and
analysis model for traffic operations, was developed by TRRL
to optimally determine fixed-time traffic control (cycle length, offsets, and
splits) [web:
UK version ;
US version ].
|
|
The official FHWA version of TRANSYT
combines signal optimization with macroscopic simulation, incorporating
platoon dispersion and queue spillback. The objective function can include
signal progression, delay and stop reduction, fuel consumption variables to
obtain an optimal fixed-time signal plan [web:
US version ].
|
|
A land use model software package developed by de la Barra (1990), based on
a spatial input-output framework. Similar packages include
MEPLAN, MUSSA,
UrbanSim, PECAS, and
ITLUP
[ web ].
|
|
A primary component of household travel surveys, the travel and
activity diary records all trips and activities for all household members for one
or more days. In the past, diaries recorded daily travel behavior by trips and
associated characteristics (including trip purpose). Now, most diaries record
activities and associated characteristics (including travel attributes). While in
theory the same data is collected, results suggest that activity diaries provide
a more complete recording of all travel and activity. Recent develops include the
use of GPS and the application of computer-based diaries to
complement or replace manual recording.
|
|
The travel and associated activities in which individuals engage over space and time
(see activity analysis and time use).
|
|
Travel cost can refer to the actual monetary expenditure on a trip or to a more
general measure of travel disutility. Regarding monetary expenditure, travel cost
can refer to actual out-of-pocket costs on a trip or a more complete cost accounting
of total cost. Regarding general measures, in travel forecasting
models, travel time is often individually used for travel cost
or as a component of generalized cost.
|
|
The derived demand to access locations via the transportation
system to perform activities (see demand).
|
|
The process of estimating, calibrating,
validating, and applying models of
travel demand and performance to
estimate the impacts of alternative transportation systems.
Perhaps better expressed as travel forecasting since inputs
and outputs include elements of both demand and supply.
|
|
Programs and projects to reduce transportation demand,
including ridesharing, transit service enhancements, and parking management.
Transportation Systems Management is the corresponding
supply-side process.
|
|
A (typically) mathematical abstraction of travel behavior,
based on statistical and/or algorithmic representations of observed travel patterns.
The objective is to forecast outcomes of alternate transportation
and activity system scenarios as a function of current
transportation and activity systems, empirical distributions of travel patterns
(by frequency, destination, mode, time-of-day, and route), and projections of future
socio-demographic characteristics. A misnomer since most such
models reflect both demand and supply
of transportation in a particular area at a particular time.
|
|
The process of estimating, calibrating,
validating, and applying models of
travel demand and performance to
estimate the impacts of alternative transportation systems. Also referred to
as travel demand forecasting (or travel demand modeling).
Although the basic model structure (the four step model)
appears relatively unchanged since its introduction in the 1960s, model
components and software have evolved significantly. Changes have included a
move from aggregate to disaggregate models and data, a greater behavior basis,
and more sophisticated equilibration algorithms. The evolution continues with
tour-based, activity-based, dynamic,
and microsimulation approaches.
|
|
The primary mechanism to collect data on travel behavior are travel surveys.
A Household Travel Survey provides the primary data for regional
travel forecasting model development. Other surveys include
external, transit on-board, and
commercial vehicle surveys. Travel data complements
non-travel data from census, land use, and employer surveys.
|
|
Travel time is a key determinant of travel behavior, frequently used as the sole
measure of travel cost in conventional travel forecasting.
In Transportation Systems Analysis, travel time is an output
of performance functions and an input to demand
functions, both of which are equilibrated to solve for
system flows. In the four step model,
travel time is a key variable in the trip distribution,
mode choice, and trip assignment steps, and
the basis for feedback in the model system. Mean travel time
(overall, by time-of-day, by trip type, etc.) is a key
performance measure in alternatives analysis
and system evaluation. See value of time.
|
|
A mathematical function of travel time used in
spatial interaction models, with standard forms including
inverse power, negative exponential,
and combined gamma functions, as well as
friction factors.
|
|
The degree of certainty or predictability of travel times
in a transportation system.
|
|
A classic problem of operations research that seeks the minimum
cost route between multiple network locations, visiting each location only once
and returning to the starting point. An NP-Hard problem solved
via dynamic programming, heuristic algorithms, and a variety of other approaches.
|
|
The Transportation Research Board, a branch of the National
Academy of Science, promotes innovation and progress in transportation through
research and facilitates the sharing of information on transportation practice
and policy [ web ].
|
|
See Minimum Path Tree.
|
|
A regular pattern evident in data that can be associated with an hypothesized
system behavior and thus can be used to predict future states of the system
(see trend projection).
|
|
Applying statistical methods to identify and extrapolate
trends in observed data, such as using a time-series model to predict a future
state. Used for demographic projections (such as population projection via
linear, exponential, or logistic
models) and for forecasting other inputs to transportation models (such as
auto ownership or labor force participation rates).
|
|
A movement by an individual from one location to perform an
activity at a different location. The fundamental
unit of analysis in conventional travel forecasting.
|
|
Trip Assignment (TA), the fourth step in the conventional
four step model of travel forecasting, is a process by
which trips, defined by time-of-day and mode, are loaded
on feasible paths between an origin and a destination in a network.
The output of assignment is the number of vehicle-trips (or passenger-trips)
allocated to paths and links on a modal network, as well as associated
performance measures (such as VMT and
travel time).
Also known as traffic assignment or Network Assignment
(see also route choice).
|
|
A trip generated (typically) by a household has both a production
and an attraction. The number of trip attractions in a zone is
proportional to the level of activity (land use) in that zone associated with the
type of trip in question. If the trip maker's residence (home) is one end of the
trip, then the other trip end is the attraction. If the trip maker's residence (home)
is at neither trip end (i.e., a NHB trip), then the attraction is
the same as the trip destination. Trip attractions are typically
represented as aggregate regression models using data pooled from zones into
districts (since travel surveys are residential-based, there
are usually not enough observed attractions in all zones to estimate zonal attractions
directly. See also production or origin.
|
|
In trip generation, separate models are estimated for
trip productions and trip attractions, for
each defined trip purpose, as a function of activity (and in
theory LOS characteristics). Trip attraction models are usually
regression models expressed at the zonal
level, often as a function of employment variables.
|
|
In trip generation, trip productions and
attractions are independently estimated, thus, for a given
trip purpose, total productions will not equal total
attractions. Since productions are typically considered to be more accurate
estimates, zonal attractions are normalized so that total
attractions are balanced with total productions for each trip purpose.
Typically, trip balancing reflects both internal
and external trips.
|
|
The predominant framework for travel forecasting models used
in practice, trip-based models reflect the basic assumptions of the
four-step model and focus on individual trips, not trips
linked into tours nor the activities
that generate these trips. Compare with tour-based and
activity-based models.
|
|
An individual's process of linking trips and non-home activities into sequences
without intervening trips returning to home. A trip chain
(or tour) is defined such that the destination of the first
trip becomes the origin of the second (a simple round trip is a trip chain with
one non-home activity). From a policy viewpoint, multiple-activity trip chains
are more efficient than a series of single-activity round trips.
|
|
Trip Distribution (TD) is the second step in the conventional
four step model of travel forecasting. TD is the process
of pairing generated productions and attractions (or origins and destinations)
to determine the number of trips between all pairs of zones in the study area.
The primary TD output are trip tables (typically 24-hour
person trips, specified by trip purpose).
TD follows trip generation in the four step model sequence,
and is followed by mode choice or time-of-day
factoring. The gravity model is the most common tool applied.
In disaggregate terms, it is the process by which a trip's destination is selected,
given the trip's purpose, origin, and travel cost to possible
destinations.
|
|
Either end of a trip. In trip generation,
trips are represented as trip ends, with
origins (or productions) modeled separately
from destinations (or attractions).
Trip end mode choice models were applied to the trip ends
produced in trip generation rather than the more conventional trip interchange
mode choice models that were applied after trip distribution.
|
|
The number of trips per unit time (typically, daily trips).
|
|
Trip Generation (TG) is the first step in the conventional
four step model of travel forecasting. TG is the process of
estimating trip productions (or origins)
and attractions (or destinations)
for all zones in the study area. In regional travel forecasting
studies, category or regression models are
applied to estimate trip ends by trip purpose
as a function of individual, household, or zonal socio-economic, land use, or
accessibility characteristics (results are typically aggregated to the zone level).
In traffic impact studies, land use-based trip rates (such as
ITE) are applied at the project or parcel level in place of regional
TG models. The outputs of trip generation analysis ("Os and Ds" or "Ps and As") serve
as input to the second step of the four step process, trip distribution.
|
|
A cell of a trip table indicates a trip interchange, the
total number of trips from an origin
(or production) to a destination (or
attraction). Interchanges are estimated in
trip distribution.
|
|
A graphical or tabular display of travel times or trip distances, typically
represented in discrete categories. TLFDs are used in the calibration of
gravity trip distribution models.
|
|
A trip generated generally by a household as a function of household socio-economic
or residential land use characteristics. If the trip maker's residence (home) is
either end of the trip, then that location or zone is the production. If the trip
maker's residence (home) is at neither trip end (i.e., a NHB trip),
then the production location is the same as the trip's origin
(compare with attraction and destination).
|
|
In trip generation, separate models are estimated for
trip productions and trip attractions, for each
defined trip purpose, as a function of activity (and in theory
LOS characteristics). Trip production models are typically
category models expressed at the household
level, usually as a function of household characteristics.
|
|
The purpose of virtually any trip is the activity in which the trip maker will
participate at the location of the end of the trip. The demand for the trip is
derived from the demand for the activity. Conventional
travel forecasting models often employ aggregate trip purposes
in lieu of actual trip purposes. Such purposes usually identify both ends of the
trip preceding the activity, such as home-work (or HBW),
home-other (or HBO), or non-home-based (or NHB).
Many larger metropolitan areas use additional purpose categories.
|
|
For a specified land use or geographic area, a trip rate is the number
of trips per unit time, typically scaled per areal or other unit. For example,
the number of vehicle-trips entering a 7-11 store in a peak hour for every 1000
square feet of retail floor space. Trip rates may be expressed as mode-specific
or by time of day. The Institute of Transportation Engineers (ITE) publishes a
widely-used compendium of average trip rates for a variety
of land uses and land use characteristics. Trip rates, in general, are modeled
in the four step model in trip generation
via techniques such as category analysis (which yields a trip
rate model).
|
|
A decrease in the number of trips (typically vehicle trips in peak periods)
resulting from policies to reduce congestion
(such as alternative work schedules).
|
|
A matrix of trips from each origin
(or production) to each destination
(or attraction) in a region (also thus referred to as
O-D or P-A matrices). Trip tables may
be specified for a particular trip purpose, time period, or mode, and for person-
or vehicle-trips. Trip tables are produced in trip distribution
models (and modified in subsequent steps of the four step model).
Trip tables may also be estimated or
updated using traffic counts.
|
|
The UK's Transportation Research Laboratory, formerly
the Transportation Road Research Laboratory
(TRRL) [ web ].
|
|
The UK's Transportation Road Research Laboratory,
now renamed the Transportation Research Laboratory
(TRL) [ web ].
|
|
Traffic Software Integrated System, a traffic
simulation software suite integrating CORSIM and support
utilities [ web ].
|
|
Texas Transportation Institute,
TTI's Urban Mobility Report is an annual assessment of
traffic congestion in metropolitan areas.
|
|
The trajectories of vehicles approaching an intersection. For a typical 4-way
intersection, each approach has left-turn, thru, and right-turn movements. Field
surveys provide these basic inputs to traffic signal optimization
and intersection capacity analysis.
|
|
In standard travel forecasting, intersection movements are not explicitly modeled.
Turn penalties and prohibitions are introduced to partially
capture intersection behavior. A turn penalty is a specified increment
added to the path travel time of traffic being assigned from an intersection
approach link to an intersection exit link, corresponding to a turning movement
that is subject to an average delay at the real intersection.
|
|
In standard travel forecasting, intersection movements are not explicitly modeled.
Turn penalties and prohibitions are introduced to partially
capture intersection behavior. A turn prohibition is a flag that prevents
traffic from being assigned from an intersection approach link to an intersection
exit link, corresponding to a turning movement that is prohibited at the real
intersection.
|
|
A macroscopic traffic flow model proposed
by Herman and Prigogine (1979) based on analogy to molecular behavior in fluid
condensation (Bose-Einstein), where the velocity of moving vehicles is related to
the proportion of stopped vehicles, fs, or:
vr = vmax [ 1- fs ]n
|
|
The error of rejecting the null hypothesis (H0) when it
is actually true. Level of significance is the probability of committing a
Type I Error and defines the critical region for rejecting H0
(see Type II Error).
|
|
The error of accepting the null hypothesis (H0) when it
is actually false. The power of the test is the probability of not committing
a Type II error (see Type I Error).
|
|
| U | [ back to top ] |
|
|
A "shared economy" technology firm that provides transport
services for profit where the economic transaction ("sharing") is between the technology
provider, a contracted physical provider, and a customer paying for the service.
(see also Lyft). The technology is a smart phone application that
links customers seeking immediate transportation with affiliated drivers in the vicinity.
|
|
The University of California Transportation Center
[ UCTC web ], one of 13 regional
University Transportation Centers (UTC)
[ UTC web ].
|
|
User Equilibrium (AKA Deterministic User Equilibrium)
(see UE).
|
|
A GIS-based travel demand modeling system that integrates node-based delay and GPS
data handling. Developed by RST [ web ]. Other
travel forecasting packages include Cube, EMME/2,
MinUTP, QRSII, T-Model,
Tranplan, and TransCAD.
|
|
Unified Mechanism Of Travel, a model proposed by Zahavi
(1979) based on aggregate relationships involving travel time and money budgets,
and other parameters claimed to be transferable over time and space.
|
|
The former Urban Mass Transportation Administration,
currently the FTA, in the US DOT.
|
|
An estimator is unbiased if its expected value is equal to the
population parameter.
|
|
A non-linear single-regime traffic stream model
developed by Underwood (1961), relates space mean speed
to density, addresses limitations in
Greenberg's model, and is incorporated in
Edie's two-regime flow model.
Underwood: u = uf exp(-d/dm) where uf is
mean free speed; dm is density at max flow.
|
|
An MPO's management plan to coordinate tasks in the overall
transportation planning and programming process for the metropolitan area.
|
|
Travel time per unit of distance, the inverse of speed,
expressed in minutes per mile.
|
|
A journey by transit from an origin to a destination may have multiple segments
that are completed on different vehicles or modes. The overall O-D journey is
one linked trip comprising multiple unlinked trip
segments (and multiple transit boardings).
|
|
Traffic or infrastructure that is located behind the current position, opposite
the direction of movement (as opposed to downstream traffic
or infrastructure that is ahead of the current position in the current direction
of movement).
|
|
Unified Planning Work Program
(see UPWP ).
|
|
Developed areas such as cities and towns that exceed a defined
population (e.g., 50,000 people within a defined boundary) or
density (e.g., 1,000 people per square mile) threshold
(see metropolitan classification).
|
|
The integrated spatial pattern of urban activity and
transportation systems.
|
|
A defined boundary around a metropolitan area intended to accommodate projected
population and employment growth within a defined planning period. Such a
smart growth strategy is intended to control sprawl
beyond the boundary.
|
|
The Texas Transportation Institute's (TTI)
Urban Mobility Report is an annual assessment of congestion in metropolitan
areas [ web ].
|
|
Controversial urban land redevelopment programs, implemented in the post-war
decades, that brought freeways and public housing projects to many cities.
|
|
An often pejorative term referring to the expansive growth of a metropolitan region.
The development of most American suburban areas is considered sprawl.
|
|
An urban design concept characterized by medium density, mixed use zoning
and a strong orientation toward the use of transit and walking. A variation
on Neo-traditional Design, New Urbanism,
and Transit-Oriented Development.
|
|
A densely settled area that contains 50,000 or more people, as delineated by
the Census Bureau.
|
|
A comprehensive land use model software package developed by Waddell (2000)
utilizing a micro-simulation approach to modeling transportation and land use
interactions. Similar packages include MEPLAN,
MUSSA, PECAS, TRANUS,
and ITLUP [ web ].
|
|
The United States Department Of Transportation,
includes FHWA, FTA, and other transport
agencies. All states have an equivalent agency, in most cases also named a
DOT [ web ].
|
|
A user equilibrium (UE) trip assignment satisfies
Wardrop's 1st Principle that states, for a given
origin-destination pair, that travel times are equal on all paths actually
utilized, and are less than or equal to the travel time on any other paths.
A UE assignment is optimal for individual travelers and is also a
Nash Equilibrium, since no traveler can improve his travel time
by unilaterally changing routes (see also system-optimal).
|
|
[1] Urban Traffic Control, the general term for the hardware
and software systems and algorithms for the coordinated operation of traffic
signals in congested areas, historically by centralized control but increasingly
with distributed localized control.
[2] The University Transportation Centers program, created
to advance US technology and expertise in transportation through education,
research, and technology transfer at university-based centers of excellence
[ UTC web ].
|
|
Urban Traffic Control System, an arterial network
simulation model developed by FHWA in the 1970s to facilitate
the development and evaluation of advanced, urban traffic control systems.
UTCS-1 evolved into NETSIM that, together with
FRESIM (which evolved from the freeway simulation model
INTRAS), formed the integrated software suite TRAF (now
TSIS/CORSIM).
|
|
The value to a decision maker of a particular choice alternative. A rationale
decision maker is assumed to maximize utility when making a
choice. A utility function expresses this unobserved utility as a function of
characteristics of the alternatives in the decision maker's
choice set as well as characteristics of the decision maker.
|
|
Standard economic assumption that decision-makers always seek to maximize overall
utility when faced with a choice situation. Utility maximizing models reflect both
observed choice attributes and error terms to reflect differences in decision-maker
perceptions. Compare with bounded rationality and
satisficing approaches.
|
|
The Urban Transportation Modeling System is a
generic name for the formal application of conventional travel forecasting
models. UTPS was the first computer implementation of,
and became synonymous with, UTMS. Currently, a more common generic name is
the four step model.
|
|
The Urban Transportation Planning System, one of the
first travel forecasting modeling packages, was developed in the 1970s by the US
Department of Transportation. Its widespread use in the first travel forecasting
led to its name becoming synonymous with the modeling process itself. Designed
for mainframe computers, UTPS has been replaced by various PC or workstation-based
software packages (e.g., see TransCAD).
|
|
| V | [ back to top ] |
|
|
An independent test of a calibrated model's predictive
capabilities using data that was not used in estimating or calibrating the
model. The objectives are to verify that the model can replicate observed
system performance and that the model is sensitive to proposed changes in
model variables, parameters, and constraints. While model
estimation and calibration might occur every
10 years, model validation should be completed prior to any forecasting
application within that period. Validation is often
linked with elements of calibration: if model predictions are no longer
within acceptable error bands, then model parameters should be re-calibrated.
Note: In travel forecasting, model validation usually
has involved only an assessment of the ability of the model to replicate observed
system-level performance and often only the outputs of the final steps (e.g.,
trip assignment) are validated. Instead, a range of model
sensitivity and reasonableness tests
are conducted to assess the ability of the model to properly reflect policy
changes in forecasting.
|
|
The economic value of a final or intermediate output minus the value of all
intermediate inputs, reflecting the contributions of the factors of production
(labor, capital, land, and entrepreneurship).
|
|
The opportunity cost of travel time, value of time is
the monetary amount that a traveler would be willing to spend to save time (e.g.,
the marginal rate of substitution between time and cost). VOT
is a parameter used in benefit-cost analysis to quantify
travel time benefits of transportation infrastructure and service improvements.
|
|
A euphemism for congestion pricing, the operational policy
of tolling facility use via fees that vary with the level of congestion or, by
proxy, by time of day. Increasingly associated with managed
lanes that parallel unpriced lanes, emphasizing the value tradeoff between travel
time and cost.
|
|
A video traffic detection system that automates the process of vehicle
detection and traffic data collection in lieu of loops
[ web ].
A similar systems is Autoscope
[ web ].
|
|
Costs that vary based on the level of transportation operations
(such as fuel or labor costs). Also known as operating costs. Compare to
fixed cost.
|
|
An expression for demand that is sensitive to cost. In
standard trip assignment, demand is fixed and represented
by static trip tables. Variable demand can be modeled
with feedback or by using a combined distribution/assignment
procedure (such as Evan's). Same as elastic demand.
|
|
In trip assignment, an alternative but equivalent mathematical
formulation of the user equilibrium problem.
|
|
[1] A scalable graphic data format comprising geometric objects such as points,
lines, and polygons, in contrast to raster format
(comprising a rectangular grid of pixels).
[2] in matrix algebra, a single column or row or any given length.
|
|
One vehicle traveling for one hour. Total vehicle-hours traveled, or
VHT, is an indicator of system performance measuring the
total amount of vehicular travel in a region based on total time spent traveling.
|
|
Development and application of communication between vehicles and roadside
infrastructure to improve safety and efficiency of the transportation system
(see IntelliDrive)
[ web ].
|
|
One vehicle traveling one mile. Total vehicle-miles traveled, or
VMT, is an indicator of system performance measuring
the total amount of vehicular travel in a region based on distance traveled
(see person-mile).
|
|
A class of OR problems to find the routes that minimize the total
cost of assigning fleet vehicles from one or more depots to multiple demand points
such that each point is visited only once by a single vehicle, all routes start and
end at a depot, and the total demand does not exceed total vehicle capacity. The
Traveling Salesman Problem is a well-known special case. The
Vehicle Routing Problem with Time Windows (VRPTW) has been used in activity-based
modeling (see HAPP) as well as in numerous OR applications.
|
|
A single trip by a single vehicle, regardless of the
number of occupants of the vehicle. A vehicle with three occupants on the
same trip equals one vehicle-trip or three person-trips.
The inputs to trip assignment are vehicle-trips for
highway modes and person-trips for non-vehicular modes.
|
|
The design of a roadway alignments in the vertical plane, including grade
tangent sections and parabolic vertical curves, and reflecting topography,
safety, facility type, speed, and other design concerns (see
horizontal alignment and
cross-sectional design).
|
|
Vehicle-hours traveled. VHT is a common performance
measure for traffic flow indicative of the total amount of travel in a region
(see VMT).
|
|
Vehicle Infrastructure Integration (see VII).
|
|
An alternative to tree-based path algorithms, vine-based algorithms
are designed to allow paths to pass through nodes more than once to accommodate
turn-prohibitions.
|
|
An activity-based travel forecasting software package, linked with
VISUM, a comprehensive travel forecasting
software package.
Developed by PTV [ web ].
|
|
[1] The process of defining and documenting values, goals and objectives, and plans.
[2] Software for displaying graphic representations of systems or system components.
|
|
A traffic microsimulation software package, linked with
VISUM, a comprehensive travel forecasting
software package.
Developed by PTV [ web ].
Other traffic microsimulation packages include AIMSUN,
CORSIM, Cube Dynasim,
Paramics, SimTraffic,
and TransModeler.
|
|
Techniques used in the development and presentation of transportation programs,
plans, and designs to analysts, stakeholders, and the public
in an accessible, graphical format to improve comprehension and evaluation.
|
|
A comprehensive travel forecasting software package, integrated with
VISSIM, a traffic microsimulation software
package, and VISEM, an activity-based travel
forecasting software package.
Developed by PTV [ web ].
|
|
Variable Message Sign (same as CMS).
|
|
Vehicle-Miles Traveled. VMT is a common aggregate
performance measure indicative of the total amount of
travel (in vehicle-miles) in a region.
|
|
Volatile Organic Compounds are a broad family of both
human-made and naturally-occurring chemical compounds, including
hydrocarbons (HC) and reactive organics
(ROG) which are contributors to the creation of smog.
|
|
The number of units of flow (e.g., vehicles) passing a defined
point (or over a uniform roadway segment) during a defined time period, typically
measured in flow units (vehicles) per hour (vph) (see also LOS
and capacity).
|
|
The ratio of volume to capacity for a given
transportation facility. A common performance measure used in
assessing network performance output from four step models and
a key variable in modeling link and intersection performance.
|
|
A link performance function, a functional performance
relationship between level-of-service and volume for a
specific facility.
|
|
Von Thünen's (1826) idealized land use model of a
monocentric agricultural region introduced fundamental land
economics to the relative location of land uses. Bid-rent
functions reflecting production and transportation costs, together with commodity
and land consumption demands, are used to determine land use, land rents, and
market prices. Comparable urban models were developed by Wingo, Alonzo, and others
(see also Central Place Theory ).
|
|
| W | [ back to top ] |
|
|
Wide Area Augmentation System (see DGPS).
|
|
The portion of a trip, often by public modes, that is spent waiting for the arrival
of a vehicle (during access/egress or transfer). Disutilities
are in general highest for waiting time.
|
|
A compact development pattern of mixed land uses that supports pedestrian
and other non-motorized transportation.
|
|
The defined maximum distance that a pedestrian is willing to walk to access a
bus stop (or other transit system) or an activity location.
|
|
Wardrop's (1952) First Principle is equivalent to user equilibrium
assignment; Wardrop's Second Principle is equivalent to system optimal
assignment.
|
|
Selected iterative trip assignment algorithms such as
origin-based assignment can significantly reduce computation
time when a base equilibrium solution is saved and used as a "warm start" in
model feedback or forecasting.
|
|
Minimum criteria necessary to authorize a roadway infrastructure or operational
change such as installation of a traffic control device. Criteria are often
based on performance measures such as average speeds, traffic
volumes, or accident levels.
|
|
World Conference on Transportation Research
Society, a international forum for the promotion of transportation
research and practice, including the organization of triennial research
conferences and publishing the journal Transport Policy
[ web ].
|
|
The estimation of vehicle and load weight while a truck is in motion.
|
|
Technologies for the interoperability of wireless, local
area networks based on IEEE 802.11 standards.
|
|
Weigh-In-Motion (see WIM).
|
|
A sub-area model extracted from a larger model by defining greater detail in the
transportation and activity systems within
the window and deleting external areas, a process equivalent to
sub-area extraction. Compare to focus model.
|
|
A GIS-based software package designed to investigate alternate development
patterns and associated land use, population, and employment projections
[ web ].
|
|
An international organization to promote the advancement of women in the field
of transportation [ web ].
|
|
Women's Transportation Seminar, known familiarly as
WTS [ web ].
|
|
| X, Y, Z | [ back to top ] |
|
|
Zero Emission Vehicle. A vehicle with no tailpipe emissions
(typically, an electric vehicle).
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An operational, research-oriented, shared-use,
station-car program in Irvine, CA that utilizes
electric vehicle, hybrid, and hydrogen-fueled vehicles
[ web ].
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A national car sharing company
[ web ].
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The basic geographical unit of analysis for conventional travel forecasting.
All locations in a study area are contained in one and
only one analysis zone, the number and size of which depend on the scale and
scope of the modeling effort. Zones should be as homogenous as possible with
respect to the associated travel behavior. Most often referred to as Traffic
Analysis Zones (TAZs).
See also census tract.
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The general term for land use regulation, with authorized land
use designations defined spatially (in "zones"). Applied at the local level (city
or county), zoning serves to control the compatibility of neighboring land uses
as well as the overall distribution of land use. Zoning regulates land use density
via requirements for setbacks, floor-area ratios, and height
restrictions, as well as transportation attributes such as parking and
site access. See Euclid v Ambler.
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The standard unit of measure to quantify container traffic flows.
One (8 foot by 8 foot by) 20-foot long shipping container equals one
20-foot Equivalent Unit (TEU).
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The Continuing, Comprehensive, and Cooperative transportation
planning process, mandated in the Federal-Aid Highway Act of 1962 and representing
the first legislation requiring a formal planning process as a pre-requisite to
receiving federal funding.
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The 3D process is a method for assessing travel impacts relative to changes in
measures of the built environment. The original 3D measures were
density, diversity, and design
(a fourth D was added as Destination accessibility).
The methodology utilizes a compilation of elasticities of vehicle
trip rates and VMT relative to the defined
"D" measures. These impacts are typically not captured in the standard
four step model. See also 4D Process.
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The conventional model for travel forecasting, so named for the four major steps
of the process: trip generation, trip distribution,
mode choice, and trip assignment.
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The 4D process assesses potential travel impacts of proposed
changes in the built environment by applying elasticities
(drawn from case studies or estimated locally) that reflect expected changed in
trip rates, VMT, or other performance measures for a percent change in planning
variables that measure density, diversity,
design, and destination accessibility.
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The 4D process is an extension of the 3D Process that reflects
a fourth measure of the built environment, Destination accessibility).
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An extension of the 4D Process as implemented in the
INDEX software. The fifth measure of the built environment
is distance from a heavy rail transit station.
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A nationwide 3-digit telephone number assigned by the FCC for traffic information
[ web ;
LA ].
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The speed at or under which 85 percent of free-flowing traffic are traveling,
representing a common standard for setting safe speed limits.
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Section 802.11 (a, c, g) of the IEEE standards
corresponding to local area communication standards, known familiarly
as Wi-Fi.
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Symbol representing the Activity System in the Manheim/Florian
framework for transportation systems analysis, constituting the
land uses and activities in a region, excluding only the
Transportation System T.
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Symbol representing the Transportation System in the Manheim/Florian framework
for transportation systems analysis, constituting the networks
(modes, links, nodes, etc.) connecting a region's Activity System.
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A | B | C | D |
E | F | G | H |
I | J | K | L |
M | N | O | P |
Q | R | S | T |
U | V | W | X |
Y | Z | # |
terms of use ]
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NOTE:
This glossary has been compiled over many years of teaching courses
on travel forecasting. Several text books and other glossaries have served as additional sources
of ideas and information, however, all entries in this glossary have been newly defined in an
consistent structure oriented toward transportation planning and modeling, as practiced in the
United States, in general, and in California, in particular.
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