working paper

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 that depend on subject 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 itineraries the results provide much higher resolution 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 OD matrix, and a detailed temporal distribution of activity participation and travel, given a set of desired destinations and schedules.

working paper

Strategic Hydrogen Refueling Station Locations Analysis with Scheduling and Routing Considerations of Individual Vehicles

Abstract

Set Covering problems find the optimal provision of service locations while guaranteeing an acceptable level of accessibility for every demand points in a given area. Other than reliance on static,exogenously-imposed accessibility measures, these problems either exclude substantive infrastructure-vehicle interactions or only include fragmented infrastructure-vehicle interactions related to the routing considerations of households seeking refueling service as a requirement of performing routine, daily activities. Here, we address this problem by coupling a Location-Routing Problem (LRP) that uses the set covering model as a location strategy to the Household Activity Pattern Problem (HAPP) as the mixed integer scheduling and routing model that optimizes households’ participation in out-of-home activities. The problem addressed includes multiple decision makers: the public/private sector as the service provider, and the collection of individual households that make their own routing decisions to perform a given set of “out-of-home activities” together with a visit to one of the service locations. A solution method that does not necessarily require the full information of the coverage matrix is developed to reduce the number of HAPPs that needs to be solved. The performance of the algorithm, as well as comparison of the results to the set covering model, is presented. Although the application is focused on identifying the optimal locations of Hydrogen Fuel Cell Vehicle (HFCV) refueling stations, this proposed formulation can be used as a facility location strategy for any service activity that is generally toured with other activities.

research report

Deployment of a Tool for Measuring Freeway Safety Performance

Abstract

This project updated and deployed a freeway safety performance measurement tool, building upon a previous project that developed the core methodology. The tool evaluates the cumulative risk over time of an accident or a particular kind of accident. The probability is estimated using a model that takes as input only variables that are derived from common inductive loop detectors. The estimated models predict increased risk of any accident occurring, as well as a number of characteristics of those accidents. By using this safety performance measurement tool, Caltrans will be able to evaluate the safety impacts of roadway changes over time. Specifically, it is anticipated that new deployments of intelligent transportation systems elements can be evaluated for their safety impacts by comparing the net risk of different kinds of accidents before and after deployment. The model predictions are best used to evaluate the cumulative probability of accidents and accident characteristics over longer time horizons and extended stretches of roadway.

Phd Dissertation

Integrated Modeling of Air Quality and Health Impacts of a Freight Transportation Corridor

Abstract

Due to environmental concerns, transportation studies have extensively evaluated emission impacts associated with traffic operational strategies and transportation policies. However, the impact studies mainly relied on emission impacts found using demand forecasting models. Such planning models cannot capture individual vehicles. interactions (i.e., lane changes or stop-and-go movements) or detailed traffic operations such as with traffic signals. These limitations often lead to under-estimated emissions while evaluating several policies. Even though many studies utilized microscopic traffic models to better estimate emissions, the studies have not considered further steps such as air quality estimation and health impact studies. This research develops an integrated framework for evaluating air quality and health impacts of transportation corridors using a microscopic traffic model, a micro-scale emissions model, a non-steady state dispersion model, and a health impact model. The main advantage of this approach is to better estimate air quality and health impacts from vehicle interactions and detailed traffic management strategies. As a case study, we evaluate air quality and health impacts of several scenarios associated with major transportation corridors accessing the San Pedro Bay Ports (SPBP) complex, California. The study context consists of two 20 miles-long major freight freeway corridors and nearby arterials, as well as line-haul rail along the Alameda corridor and several rail yards associated with the SPBP complex. For the scenarios, we consider a clean truck program, cleaner locomotives, and modal shifts compared to the 2005 baseline. All scenarios performed with the integrated framework have provided larger improvements of air quality and health impacts associated with transportation corridors than conventional frameworks using transportation planning models. However, the difference in air quality and health impacts from modal shift scenarios between clean trucks and locomotives are minor. As exploratory research, pollution response surface models are developed. The main objective of the pollution response surface model is to avoid the high computational cost of the microscopic traffic model, which makes it difficult to estimate traffic for multiple days needed for evaluating emissions and health impacts over longer periods such a climate season. A conceptual framework for estimating pollution response surface models is proposed. Using a hypothetical network, response surfaces of NOX and PM are estimated.

Phd Dissertation

An Analysis of the Impact of an Incident Management System on Secondary Incidents on Freeways – An Application to the I-5 in California

Abstract

Accidents are the largest source of external costs related to transportation in the United States with annual costs estimated to exceed $200 billion per year. Incidents also create traffic backups and delays that can result in secondary incidents (i.e., collisions that occur as a result of other incidents). Although incident management has received a lot of attention from academics and practitioners alike, secondary incidents have so far been somewhat neglected. The main purpose of this dissertation is to investigate empirically whether the implementation of changeable message signs (CMS), which are one Intelligent Transportation System tool, can reduce secondary collisions. After reviewing previously published methods for estimating secondary accidents, I implement a Binary Speed Contour Map approach to detect secondary incidents using PeMS data. I also estimate the extra time lost to congestion because of incidents. My study area is a portion of Interstate 5 that stretches 55 miles from the Mexico-US border to Northern San Diego County, CA. This freeway portion has an x average annualized daily traffic volume of 230,000 vehicles. My unique dataset includes incident data for 2008 combined with detailed weather data, elements of freeway geometry, and information about CMS usage. I identify a total of 9,003 incidents in my study area in 2008. Using the BSCM approach, I find that 3.7 percent of collisions were secondary incidents. Moreover, my statistical model shows that incidents occurring during evening peak hours on Fridays or during midday on weekends are more likely to result in secondary crashes as do incidents with injuries or fatalities, incidents that involve more vehicles or trucks, or incidents that take place when the pavement is wet. Conversely, secondary crashes are less likely to occur in areas with a complex geometry (perhaps because drivers are more cautious there) or for incidents taking place on the side of the freeway. More importantly, changeable message signs (CMS) decrease the occurrence of secondary crashes. The maximum effectiveness of a CMS is approximately 11.75 miles for a range of 23.6 miles. Finally, annual incident-related congestion is approximately 1.9 hours per freeway vehicle, which represents five percent of the 37 hours of annual traffic delay experienced by the average San Diego motorist.

conference paper

Development of a real-time on-road emissions estimation and monitoring system

Abstract

Transportation has been a significant contributor to total greenhouse gas and criteria air pollutant emissions. Emission mitigation strategies are essential in reducing transportation’s impacts on the environment. In order to effectively develop and evaluate on-road emissions reduction strategies, it is important to have an information support system which can estimate and monitor on-road emissions under real world traffic operations. Emission data provided by such a system can be used to identify emission hot spots and their causes, and to develop and evaluate reduction strategies. In this paper, a system is developed to estimate and monitor operational on-road emissions with high accuracy and resolution in real time. The two sets of critical information for emission estimation, vehicle mix and vehicle activity, are directly generated from traffic detection using inductive vehicle signature technology. An initial implementation on a section of the I-405 freeway at Irvine, California is demonstrated. With more widespread deployment, the system can be used to perform before-and-after evaluation of certain mitigation strategies, to develop time sensitive optimal traffic control strategies with the purpose to control emissions, and to provide high fidelity greenhouse gas and air quality information to policymakers, researchers, and the general public.

Phd Dissertation

Of Planes, Trains and Automobiles: Market Structure and Incentives for a more Efficient, Cleaner and Fairer Transportation System

Publication Date

August 24, 2011

Author(s)

Abstract

The unifying theme of this dissertation’s three applications of economics to transportation is an attempt to make transportation more efficient, environmentally friendlier and fairer. In my first essay, I apply game theory and the notion of Cournot equilibrium to transportation. I compare two networks, hub-and-spoke and a point-to-point network, which is served by two non-cooperative transportation firms. I find that the way in which two firms set their respective network, either direct indirect service, has an effect on their costs and profits. In my second essay, I analyze the ownership of hybrid electric vehicles by U.S. households using the 2009 National Household Travel Survey to understand the impact of various government policies aimed at increasing hybrid vehicle ownership, such as granting access to high-occupancy vehicle lanes, tax credits, and parking incentives. I use a logit model; explanatory variables include socio-economic characteristics, along with urban form, as well as policy variables. Understanding which policies are most cost-effective at fostering HEV ownership would allow policy makers to make effective use of public resources. 2 In my third essay, I address equity in transportation by stratifying the NHTS into three income groups: low-income, middle-income and upper-income. The purpose is to determine whether income affects travel behavior. I analyze questions in the 2009 NHTS that were not available in previous NHTS surveys. These questions inquire about internet use, medical condition and physical activity. I also estimate a series of logit models and find that those living in poverty and who report having a medical condition are more likely to make medical trips. Upper-income individuals are more likely to report social and recreational trips, meal and trips labeled as “other.” Analyzing trips by income is important from an equity standpoint when allocating scarce public funds for transportation projects, since it tells us what income groups are likely to be affected by specific transportation projects.

Phd Dissertation

Assessing Benefits and Costs of Urban Environmental Attributes in a Hedonic Framework: Three Southern California Case Studies

Abstract

This dissertation research focuses on understanding benefits or costs of some urban amenities and disamenities using the Hedonic Pricing (HP) method. It includes three Southern California case studies where different hedonic models (fixed effects, spatial Durbin model, and geographically weighted regression) are estimated to obtain unbiased and consistent parameter estimates. In the first case study, I analyze 20,660 transactions of single family detached houses sold in 2003 and 2004 in the city of Los Angeles, CA, to estimate the value of urban trees, irrigated grass, and non-irrigated grass areas. I rely on fine-grained hedonic models with many covariates to control for unobserved neighborhood characteristics. I find that Angelenos like lawns: 78 percent of the properties examined would gain value with additional irrigated grass in their neighborhood and even more (83 percent) on their parcel. However, additional parcel trees would decrease the value of almost half (46 percent) of the properties examined and they would have only a small positive impact on most of the others. By contrast, additional neighborhood trees would slightly increase the value of over 80 percent of the properties analyzed. This suggests that while Los Angeles residents may want additional trees, they are unwilling to pay for them. These results have implications for urban tree planting programs that rely primarily on private property owners. The second case study quantifies the impact of urban green spaces on the value of 1,197 multifamily buildings sold in 2003-2004 in the city of Los Angeles, California; these green spaces are either on their parcels or in their vicinity (an area 200 meters outward of each parcel boundary). It is necessary to examine multifamily houses separately because they belong to a different market. To assess the robustness of the results, I contrast a spatial Durbin model with a geographically weighted regression model and conduct an extensive sensitivity analysis. I find that increases in grassy areas either on the parcels of multifamily buildings or in their vicinity would typically not enhance their value, and neither would more parcel tree canopy cover (TCC); by contrast, most multifamily properties would benefit from an increase in vicinity TCC. These results suggest that most multifamily building owners have no incentives to increase the tree canopy cover or the grassy areas on their properties. In the third case study, I investigate the impact of freeway traffic on property values using hedonic pricing models, with a particular interest for truck traffic. I analyze 4,715 sales of single family houses that took place in 2003 and 2004 in part of the busy transportation corridor that links the Ports of Los Angeles and Long Beach to downtown Los Angeles. These houses are located at least 200 meters from the nearest arterial road to filter out the impact of traffic on arterial roads. In order to minimize the risk of omitted variable bias and spatial autocorrelation, I estimate a fine-grained fixed effects model. I find that a one percent increase in the proportion of truck traffic could decrease the value of a $420,000 house located between 100 and 400 meters from the nearest freeway by between $2,000 and $2,750. These results are important for policy makers and owners of single family houses located close to freeways as the ports of Los Angeles and Long Beach are forecasting sharp increases in drayage truck activity as the economy recovers.

MS Thesis

Exploratory ideas for projecting the growth of alternative fuel vehicles : an ecological perspective

Abstract

The rise of alternative fuel vehicles has had an impact on vehicle choice in recent years. The acceptance and growth of these vehicles is dependent upon many factors. In this thesis we present some ideas drawn from analogies to ecology to help explain a possible demand towards alternative fuel vehicles. More specifically, using basic growth and decay rates of species populations, we present some preliminary analysis regarding how ecological modeling may relate to the growth of hydrogen and battery electric vehicles. We build upon the dynamics of the ecology equations to postulate potential vehicle growth patterns. We generate synthetic data to demonstrate potential applications of the analogous models for real world scenarios and to predict possible outcomes. Additionally, we look at migration probabilities between different vehicle population areas to see how vehicles travel on a limited range, as well as examine a mutualism dynamic that could possibly exist between vehicles and their refueling or charging stations. It is emphasized that the work presented here is exploratory in nature, and that any actual application of the models that are developed is well beyond the scope of this thesis. Rather, our purpose is only to identify and demonstrate certain aspects of ecological modeling that may shed light on the potential for alternative fuel vehicles to gain an appreciable market share of the current internal combustion vehicle marketplace.

MS Thesis

Understanding travel behavior and vehicle emissions from GPS and diary data an application to Southern California

Abstract

The purpose of this thesis is to explore the impact of socio-economic characteristics of drivers on travel behavior and on vehicular emissions of various air pollutants using microscopic data. My starting dataset was collected by SCAG in 2001 and 2002 during their post 2000 Census Regional Travel Survey. Of the 16,939 households who answered the survey, 297 provided self-reported 24-hour travel diary data and detailed GPS data for their vehicles, which was instrumented for SCAG’s survey. After selecting 100 out of these 297 households based on their socio-economic characteristics and the completeness of their answers, I relied on 2003 imagery in Google Earth to match diary and GPS data. An extensive clean-up of this dataset yielded a sample of 701 trips, for which I estimated emissions of CO, CO₂, NOx, HC, PM₁₀, and PM₂.₅ using OpMode in EPA’s MOVES2010 (Motor Vehicle Emissions Simulator) from second-by-second GPS travel data. A statistical analysis of the results reveals that men make longer trips than women, although the difference in their emission rates is not statistically significant. Moreover, people 60 or older are the greenest drivers: their driving patterns are more environmentally benign because they accelerate/decelerate less than younger people. Finally, I found significant differences in emission rates based on different household income levels.