Phd Dissertation

The Perception-Intention-Adaptation (PIA) model : a theoretical framework for examining the effect of behavioral intention and neighborhood perception on travel behavior

Publication Date

June 14, 2013

Author(s)

Abstract

Recent research has indicated convincing evidence of a link between characteristics of the built environment and travel behavior. However, few land use – travel behavior studies include cognitive factors (such as attitudes, perceptions, and environmental norms) that have been found to affect travel mode choice in the social psychology literature. This dissertation develops and empirically tests a theoretical framework called the Perception-Intention-Adaptation (PIA) model that brings land use and attitude-behavior theory together in order to address gaps in the travel behavior literature. Following a detailed description of the PIA model, the dissertation is comprised of three empirical essays. The analyses in these essays are based on cross-sectional and panel data collected during the Expo Line Study, the first experimental-control, before-and-after evaluation of a rail transit investment in California. The first essay evaluates the predictive power of the core socio-psychological constructs of the PIA (attitudes, norms, and control beliefs) in combination with a comprehensive set of built environment and socio-economic measures. Regression models of transit use are used to analyze cross-sectional data obtained before the opening of the Exposition light rail line in Los Angeles. The analysis indicates that two PIA constructs, attitudes toward public transportation and concerns about personal safety, significantly improve the model fit and were robust predictors of transit use, independent of built environment factors. The second essay uses panel data collected before and after the opening of the Exposition light rail line to examine changes in travel behavior. A quasi-experimental approach with experimental (within ℗ư mile of an Expo station) and control (beyond ℗ư mile) households is used to evaluate the travel effects of the opening of the Expo line at the household level. The results show a statistically significant reduction in vehicle miles traveled (VMT) in the experimental group, though overall transit ridership and travel-related physical activity did not change significantly. The final essay uses the before and after opening panel data to examine socio-psychological aspects of travel behavior change in response to the Expo Line opening. Random effects models of transit use, car driver trips, and active travel trips all show that the socio-psychological constructs hypothesized in the PIA model do have a significant impact on travel behavior. In addition, cross-lagged models designed to examine the attitude-behavior relationship show an apparent causal pathway from attitudes to behavior for all three travel outcomes.

Phd Dissertation

Properties, Simulation, and Applications of Inter-Vehicle Communication Systems

Abstract

The growth of urban vehicle traffic generates serious transportation and environmental problems in most countries of the world. Intelligent transportation systems (ITS) are effective means to solve basic traffic problems, such as driving safety, road congestion, disaster supplies, emissions, etc. Inter-vehicle communication (IVC) system is one of the most important components of ITS. In recent years, the rapid development of information technologies leads a revolution in IVC, enabling IVC be a powerful multifunctional system. However, there exist numerous challenges for ITS studies. This dissertation is aimed to address three urgent and critical issues in IVC: efficiency of information exchanging among connected vehicles, simulation methods, and IVC applications. Information transmission efficiency, which can be measured by communication throughput or capacity, is a fundamental property of vehicular ad hoc networks. This dissertation theoretically analyzes communication throughputs, including broadcast and unicast communications, under discrete and continuous vehicular ad hoc networks (VANETs). We also examine influence of transmission range, interference ratio, market penetration rate of IVC-equipped vehicles, percentage of senders, and traffic waves on throughputs. Furthermore, we derive a theoretical formulation to calculate communication capacities under uniform traffic streams. And, an integer programming (IP) model is improved to explore capacities in general traffic, and a genetic algorithm is constructed to search the solutions efficiently. The second contribution of this dissertation is the development of a hybrid traffic simulation model to evaluate transportation systems incorporated with IVC technologies. As IVC-equipped vehicles are able to obtain more road information and they are controlled to pursue some objectives, they will behave differently from others, and transportation systems will become heterogeneous. This dissertation presents a hybrid traffic simulation model coupling microscopic and macroscopic models to address heterogeneity in transportation systems. In the model, equipped vehicles are regulated by a car-following model, while the other vehicles are described as continuous media with the Lighthill-Whitham-Richard (LWR) model. We analytically study the model on a single-lane road using a modified Godunov method. The hybrid model shows its potential of accurate wave propagation from individual vehicles to continuous traffic streams, and reversely; i.e., the model is capable of analyzing heterogeneous traffic. Moreover, consistency, stability and convergence of the hybrid model are carefully investigated. The model also shows the advancement of computational efficiency and control flexibility on traffic simulations. Finally, for IVC applications in environment, we propose a green driving strategy to smooth traffic flow and lower pollutant emissions and fuel consumption. In this dissertation, we study constant and dynamic green driving strategies based on inter-vehicle communications. Generally, speed limit control in successful strategies guarantee a vehicle’s speed profile be smooth while still following its leader during a relative long time period. A theoretical analysis of constant strategies demonstrates that optimal smoothing effects can be achieved when a speed limit is set to be close to but not smaller than average speed of traffic. We consider a dynamic strategy in which controlled vehicles share location and speed information based on a feedback control system. The influence of market penetration rate of equipped vehicles and communication delay on the strategy is also analyzed. Besides the development of the green driving strategy, we construct a green driving APP for smartphones on the Google Android platform and design a field experiment to check the feasibility of the strategy. The results are promising and support the advancements of IVC on reducing emissions and fuel consumption.

Phd Dissertation

Integration of Locational Decisions with the Household Activity Pattern Problem and Its Applications in Transportation Sustainability

Publication Date

June 14, 2013

Abstract

This dissertation focuses on the integration of the Household Activity Pattern Problem (HAPP) with various locational decisions considering both supply and demand sides. We present several methods to merge these two distinct areas—transportation infrastructure and travel demand procedures—into an integrated framework that has been previously exogenously linked by feedback or equilibrium processes. From the demand side, travel demand for non-primary activities is derived from the destination choices that a traveler makes that minimizes travel disutility within the context of considerations of daily scheduling and routing. From the supply side, the network decisions are determined as an integral function of travel demand rather than a given fixed OD matrix.

First, the Location Selection Problem for the Household Activity Pattern Problem (LSP-HAPP) is developed. LSP-HAPP extends the HAPP by adding the capability to make destination choices simultaneously with other travel decisions of household activity allocation, activity sequence, and departure time. Instead of giving a set of pre-fixed activity locations to visit, LSPxviii HAPP chooses the location for certain activity types given a set of candidate locations. A dynamic programming algorithm is adopted and further developed for LSP-HAPP in order to deal with the choices among a sizable number of candidate locations within the HAPP modeling structure. Potential applications of synthetic pattern generation based on LSP-HAPP formulation are also presented.

Second, the Location – Household Activity Pattern Problem (Location-HAPP), a facility location problem with full-day scheduling and routing considerations is developed. This is in the category of Location-Routing Problems (LRPs), where the decisions of facility location models are influenced by possible vehicle routings. Location-HAPP takes the set covering model as a location strategy, and HAPP as the scheduling and routing tool. The proposed formulation isolates each vehicle’s routing problem from those of other vehicles and from the master set covering problem. A modified column generation that uses a search method to find a column with a negative reduced price is proposed.

Third, the Network Design Problem is integrated with the Household Activity Pattern Problem (NDP-HAPP) as a bilevel optimization problem. The bilevel structure includes an upper level network design while the lower level includes a set of disaggregate household itinerary optimization problems, posed as HAPP or LSP-HAPP. The output of upper level NDP (level-ofservice of the transportation network) becomes input data for the lower level HAPP that generates travel demand which becomes the input for the NDP. This is advantageous over the conventional NDP that outputs the best set of links to invest in, given an assumed OD matrix. Because the proposed NDP-HAPP can output the same best set of links, a new OD matrix and a detailed temporal distribution of activity participation and travel are created. A decomposed xix heuristic solution algorithm that represents each decision makers’ rationale shows optimality gaps of as much as 5% compared to exact solutions when tested with small examples.

Utilizing the aforementioned models, two transportation sustainability studies are then conducted for the adoption of Alternative Fuel Vehicles (AFVs). The challenges in adopting AFVs are directly related to the transportation infrastructure problems since the initial AFV refueling locations will need to provide comparable convenient travel experience for the early adopters when compared to the already matured gasoline fuel based transportation infrastructure. This work demonstrates the significance of the integration between travel demand model and infrastructure problems, but also draws insightful policy measurements regarding AFV adoption.

The first application study attempts to measure the household inconvenience level of operating AFVs. Two different scenarios are examined from two behavioral assumptions – keeping currently reported pattern and minimizing the inconvenience cost through HAPPR or HAPPC. From these patterns, the personal or household inconvenience level is derived as compared to the original pattern, providing quantified data on how the public sector would compensate for the increases in travel disutility to ultimately encourage the attractiveness of AFVs.

From the supply side of the AFV infrastructure, Location-HAPP is applied to the incubation of the minimum refueling infrastructure required to support early adoption of Hydrogen Fuel Cell Vehicles (HFCVs). One of the early adoption communities targeted by auto manufacturers is chosen as the study area, and then three different values of accessibility are tested and measured in terms of tolerances to added travel time. Under optimal conditions, refueling trips are found to be toured with other activities. More importantly, there is evidence xx that excluding such vehicle-infrastructure interactions as well as routing and scheduling interactions can result in over-estimation of minimum facility requirement.

Phd Dissertation

Shared-ride Passenger Transportation Systems with Real-time Routing

Abstract

This dissertation describes a series of real-time vehicle routing problems with the associate optimization and simulation modeling for flexible passenger transport systems such as the High Coverage Point-to-Point Transit (HCPPT) and shared-taxi, which involve a sufficient number of deployed small vehicles with advanced information supply schemes to match real-time passenger demands and vehicle position for passenger transportation over large areas. HCPPT is an alternate design for mass passenger transport developed in recent years at the University of California at Irvine. The designs rely on transfer hubs, trunk route connections between the hubs where the vehicles are non-reroutable, and local areas around the hubs where the vehicles are reroutable. First, we relax the restriction in the existing heuristic rules of HCPPT, expecting to yield higher efficiency for general cases. Optimization schemes are proposed for both trunk and local vehicle routing problems to consider global optimality for large-scale problems. Significantly, the new algorithms allow globally optimal vehicle movements over multiple-hubs, unlike the earlier designs that allowed travel only to the adjacent hubs. This in turn ensures that the scheme has scalability in large areas and has design flexibility in adjusting the distances between hubs. Second, for an efficient and productive taxi system of the conventional kind, a design of shared-taxi operation is proposed, which also can be potentially used for local area operations in HCPPT. Three algorithms are developed and compared with different objective functions. Another contribution of this research is the development of a simulation platform targeting large-scale flexible point-to-point transit systems with various vehicle operation schemes. Traditionally, real-time DRT operations are simulated with commercial traffic simulators such as mesoscopic or microscopic simulation models, which is cumbersome because the available software were not designed for such real-time routed vehicle simulation, and also because they include details of less relevance to large-scale real-time Demand Responsive Transit (DRT) systems. The simulation studies in this research evaluate the vehicle routing algorithms through the proposed platform for Orange County, U.S.A. and Seoul, Korea. Finally, this thesis studies two large-scale fleet applications of Electric Vehicles (EV) as a future transportation alternative, as the hub locations which are part of the designs developed in this research are particularly suitable as energy replenishment nodes. Since EVs have a limited driving range and need to visit charging stations frequently, this part mainly focuses on the vehicle charge replenishing schedules in conjunction with passenger pickup and delivery schedules and measures the benefits from combining EVs and DRT fleets.

working paper

Density Estimation using Inductive Loop Signature based Vehicle Re-identification and Classification

Abstract

This paper presents a new method for estimating traffic density on freeways, and an adaptation for real-time applications. This method uses re-identified vehicles and their travel times estimated from a real-time vehicle re-identification (REID) system which attempts to anonymously match vehicles based on their inductive signatures. The accuracy of the section- 6 based density estimation algorithm is validated against ground-truth data obtained from recorded video for a six-lane, 0.66-mile freeway segment of I-405N in Irvine, California, during the morning peak period. The proposed density estimation algorithm results are compared against a g-factor based method which relies on inductive loop detector occupancy data and estimated vehicle lengths from the Caltrans Performance Measurement System (PeMS) as well as a selected REID method which uses a sparse REID algorithm based on long vehicle detection and volume counts at detector stations. Although the g-factor approach produces real-time density estimates, it requires seasonally calibrated parameters. In addition to the calibration effort to maintain overall accuracy of the system, the g-factor approach will also produce errors in density estimation if the actual composition of vehicles yields a different observed g-factor from the calibrated value. In contrast, the proposed method uses an existing vehicle re-identification model based on the matching of inductive vehicle signatures between two locations spanning a freeway section. This approach does not require assumptions on the vehicle composition, hence does not require calibration. The proposed algorithm obtained section-based density measures with a mean absolute percentage error (MAPE) of less than four percent when compared against groundtruth data and provides accurate density estimates even during congested conditions, improving both the PeMS and selected alternative REID based methods.

published journal article

On Activity-based Network Design Problems

Abstract

This paper examines network design where OD demand is not known a priori, but is the subject of responses in household or user itinerary choices to infrastructure improvements. Using simple examples, we show that falsely assuming that household itineraries are not elastic can result in a lack in understanding of certain phenomena; e.g., increasing traffic even without increasing economic activity due to relaxing of space-time prism constraints, or worsening of utility despite infrastructure investments in cases where household objectives may conflict. An activity-based network design problem is proposed using the location routing problem (LRP) as inspiration. The bilevel formulation includes an upper level network design and shortest path problem while the lower level includes a set of disaggregate household itinerary optimization problems, posed as household activity pattern problem (HAPP) (or in the case with location choice, as generalized HAPP) models. As a bilevel problem with an NP-hard lower level problem, there is no algorithm for solving the model exactly. Simple numerical examples show optimality gaps of as much as 5% for a decomposition heuristic algorithm derived from the LRP. A large numerical case study based on Southern California data and setting suggest that even if infrastructure investments do not result in major changes in link investment decisions compared to a conventional model, the results provide much higher resolution temporal OD information to a decision maker. Whereas a conventional model would output the best set of links to invest given an assumed OD matrix, the proposed model can output the same best set of links, the same daily OD matrix, and a detailed temporal distribution of activity participation and travel from which changes in peak period OD patterns can be observed.

MS Thesis

A Case Study of Transportation Behavior and Analysis at UC Irvine

Publication Date

March 29, 2013

Author(s)

Abstract

The purpose of this study is to provide a comprehensive analysis of UC Irvine affiliate transportation patterns and behavior. Through this analysis, recommendations on how to best promote more sustainable transportation on the UC Irvine campus was made to the two study sponsors, UCI Transportation and Distribution Services (TDS) and Anteater Express. With the assistance of TDS, an online survey was sent through a campus-wide email, and achieved overall sample size n = 2,034. Due to technical errors, freshmen did not receive the email. However, through the assistance of UCI Student Housing, surveys were sent to on-campus freshmen. Consequently, this still left out the off-campus freshmen and this exclusion impacted our analysis. Set aside from this limitation, the current study provided a framework, to the study sponsors, for an unprecedented comprehensive campus-wide transportation analysis at UC Irvine based on the study sponsor’s goals and objectives. Results indicate there is room for improving the use of alternative transportation for UCI affiliates who live within the City of Irvine in which UC Irvine is located. One recommendation pertains to increasing awareness of more sustainable transportation option and shedding light on transportation impacts early on such as during incoming student orientation and when students move out of the dorms and into local rental communities. That way when new UCI affiliates attempt to get acclimated to their new surroundings, with the early information, they can get the idea to explore alternative transportation as a potential way to be included within their daily life.

Phd Dissertation

Location Based Services in Vehicular Networks

Publication Date

March 14, 2013

Author(s)

Abstract

Location-based services have been identified as a promising communication paradigm in highly mobile and dynamic vehicular networks. However, existing mobile ad hoc networking cannot be directly applied to vehicular networking due to differences in traffic conditions, mobility models and network topologies. On the other hand, hybrid architectures in vehicular networks, with ad hoc-based inter-vehicle and infrastructure-based vehicle-to-roadside communications, can facilitate robust and efficient communication services using geographical information. In this dissertation, we focus on the design and evaluation of location-based protocols and algorithms to improve scalability, efficiency, and resiliency in hybrid vehicular networks. We first provide a cross-layer self-localization algorithm for moving vehicles. A new ultra-wide band (UWB) coding method, based on an orthogonal variable spreading factor and time hopping, is proposed for minimum interference during ranging. Then, a UWB based non-metric multidimensional scaling derives accurate and robust self-localization results. In addition, we employ an online compressive sensing scheme to count and localize sparse roadside units (RSUs) for war-driving applications. Online war-driving records received signal strength (RSS) values at runtime, and can recover the number and location of RSUs immediately based on far fewer noisy RSS readings. After obtaining the location information of vehicles and RSUs, we address multiple channel scheduling in hybrid vehicular networks. We use the natural beauty of Latin squares to achieve fair and deterministic scheduling in micro-time scale for channel access and macro-time scale for channel assignment. A grid based scalable scheme is proposed to map Latin squares to grids for dynamic single-radio multi-channel scheduling. Another interference graph based scheme uses nodal location and social centrality to reflect the social behavior patterns related to access in vehicular networks, and then form adaptive clusters for multi-radio multi-channel scheduling. We also investigate several vehicular environments, and propose corresponding location- and environment-aware data dissemination solutions. We first present an efficient on-demand bounce routing method in vehicular tunnels. It applies a hybrid signal propagation model and location-based forwarding metric to choose the best data dissemination strategy. Then, we design a hybrid routing scheme for robust and reliable data dissemination in urban transportation environments, in which the choice of communication method is dependent upon geographical connectivity, by taking network coding based multicast routing in dense network and opportunistic routing using carry and forward method in sparse network. In addition, we propose an online learning based knowledge dissemination in unmanned aerial vehicle (UAV) swarms under delay/disruption-tolerant networking, where each UAV adaptively chooses broadcast probability by learning link status. A fractionated Cyber-Physical System framework, based on partial ordering for knowledge sharing and colored Petri net for work flow, is implemented to achieve distributed knowledge management in UAV swarms. Our extensive simulation and real testbed results show the robustness and efficiency of location-based services in vehicular networks with hybrid architectures.

research report

High Occupancy Vehicle (HOV) System Analysis Tools: Statewide HOV Facility Performance Analysis

Abstract

The two most common types of high occupancy vehicle (HOV) lanes in California are continuous access, prevalent in Northern California, and buffer-separated limited access, prevalent in Southern California. This report describes the evaluation of operational performance of HOV facilities in several regions in California with different access types as well as a before-after comparative study of California facilities where access types were converted in recent years. A set of performance measures were defined and selected to indicate how well the HOV facilities achieve intended goals – congestion relief, travel time saving, greater highway capacity. Additionally, an alternative methodology of indicating how well the operations perform in terms of the traffic flow fundamental diagrams was also adopted.