conference paper
WIP: Deployability improvement, stealthiness user study, and safety impact assessment on real vehicle for dirty road patch attack
Workshop on Automotive and Autonomous Vehicle Security (AutoSec)
Publication Date
January 1, 2021
Archives: Research Products
published journal article
An instantaneous kinematic wave theory of diverging traffic
Transportation Research Part B: Methodological
Publication Date
February 1, 2013
Author(s)
Suggested Citation
Wen-Long Jin and H. Michael Zhang (2013) “An instantaneous kinematic wave theory of diverging traffic”, Transportation Research Part B: Methodological, 48(1), pp. 1–16. Available at: 10.1016/j.trb.2012.12.001. research report
Factors affecting speed of motor vehicles on urban arterials: Case of chennai, India
Publication Date
January 1, 2006
Author(s)
Suggested Citation
Michael G McNally, R Jayakrishnan, Nesamani Subramanian Kalandiyur and KP Subramanian (2006) Factors affecting speed of motor vehicles on urban arterials: Case of chennai, India. published journal article
Child serum metabolome and traffic-related air pollution exposure in pregnancy
Environmental Research
Publication Date
January 1, 2022
Author(s)
Beate Ritz, Qi Yan, Di He, Jun Wu, Douglas I. Walker, Karan Uppal, Dean P. Jones, Julia E. Heck
Abstract
Background Maternal exposure to traffic-related air pollution during pregnancy has been shown to increase the risk of adverse birth outcomes and childhood disorders. High-resolution metabolomics (HRM) has previously been employed to identify metabolic responses to traffic-related air pollution in adults, including pregnant women. Thus far, no studies have examined metabolic effects of air pollution exposure in utero on neonates. Methods We retrieved stored neonatal blood spots for 241 children born in California between 1998 and 2007. These children were randomly selected from all California birth rolls to serve as birth-year matched controls for children with retinoblastoma identified from the California cancer registry for a case control study of childhood cancer. We estimated prenatal traffic-related air pollution exposure (particulate matter less than 2.5 μm (PM2.5)) during the third-trimester using the California Line Source Dispersion Model, version 4 (CALINE4) based on residential addresses recorded at birth. We employed untargeted HRM to obtain metabolic profiles, and metabolites associated with air pollution exposure were identified using partial least squares (PLS) regression and linear regressions. Biological effects were characterized using pathway enrichment analyses adjusting for potential confounders including maternal age, race/ethnicity, and education. Results In total we extracted 4038 and 4957 metabolite features from neonatal blood spots in hydrophilic interaction (HILIC) chromatography (positive ion mode) and C18 reverse phase columns (negative ion mode), respectively. After controlling for confounding factors, partial least square regression (Variable Importance in Projection (VIP) ≥ 2) selected 402 HILIC positive and 182 C18 negative features as statistically significantly associated with increasing third trimester PM2.5 exposure. Using pathway enrichment analysis, we identified metabolites in oxidative stress and inflammation pathways as being altered, primarily involving lipid metabolism. Conclusion The metabolite features and pathways associated with air pollution exposure in neonates suggest that maternal exposure during late pregnancy contributes to oxidative stress and inflammation in newborn children.
Suggested Citation
Beate Ritz, Qi Yan, Di He, Jun Wu, Douglas I. Walker, Karan Uppal, Dean P. Jones and Julia E. Heck (2022) “Child serum metabolome and traffic-related air pollution exposure in pregnancy”, Environmental Research, 203, p. 111907. Available at: 10.1016/j.envres.2021.111907. conference paper
US household preferences for alternative-fuel vehicles: Results from a national survey
Proceedings of the 91st annual meeting of the transportation research board
Publication Date
January 1, 2012
Author(s)
Abstract
This paper analyzes responses to a 2010 national survey of 835 US households to explore consumer preferences among five types of vehicles that differ in propulsion technology (gasoline, hybrid electric (HEV), compressed natural gas (CNG), hydrogen fuel cell (HFC), and electric (EV)), vehicle cost, fuel cost, fuel availability, vehicle range, and CO2 emissions during operation. Although gasoline-fueled vehicles are still preferred, there was strong interest in alternatives to gasoline vehicles, and especially in HEVs, while EVs are least popular. The authors estimated a panel rank-ordered mixed logit model to understand the impact of vehicle characteristics and of the socio-economic characteristics of respondents on their preferences for alternative fuel technologies. With the exception of CNG, respondents prefer alternative propulsion technology in cars as opposed to pick-up trucks, sport utility vehicles (SUV), or minivans. The region where people live is not statistically significant. Education matters only in the case of HEVs, but gender has no significant impact, and the influence of age is technology specific. It was found that environmental attitudes are strong predictors of AFV support, particularly for HFC vehicles and EVs. In addition, the authors elicited trade-offs people are willing to make between vehicle cost, fuel cost, vehicle range, and refueling time. In spite of consumer interest for alternative-fuel vehicles, environmental benefits still take second place to economic considerations.
Suggested Citation
Jean-Daniel Saphores and Hilary Nixon (2012) “US household preferences for alternative-fuel vehicles: Results from a national survey”, in Proceedings of the 91st annual meeting of the transportation research board, p. 18p. conference paper
Continuum car-following model of capacity drop at sag and tunnel bottlenecks
Transportation research procedia
Publication Date
January 1, 2018
Author(s)
K. Wada, Irene Martinez, Wenlong Jin
Suggested Citation
K. Wada, I. Martínez and W.-L. Jin (2018) “Continuum car-following model of capacity drop at sag and tunnel bottlenecks”, in Transportation research procedia, pp. 668–687. Available at: 10.1016/j.trpro.2019.05.035. published journal article
Inventory planning with forecast updates: Approximate solutions and cost error bounds
Operations Research
Publication Date
December 1, 2006
Author(s)
Suggested Citation
Xiangwen Lu, Jing-Sheng Song and Amelia Regan (2006) “Inventory planning with forecast updates: Approximate solutions and cost error bounds”, Operations Research, 54(6), pp. 1079–1097. Available at: 10.1287/opre.1060.0338.
policy brief
What Should Agencies Measure to Decide if Microtransit Is Working?
Publication Date
January 1, 2026
Associated Project
Author(s)
Michael Hyland, Kari Edison Watkins, Susan Shaheen
Areas of Expertise
Abstract
California state agencies, public transit agencies, and cities have invested in dozens of microtransit pilot programs, often with the stated goals of improving access, filling gaps in fixed-route public transit service, and serving communities that are difficult to reach by traditional bus or rail. As microtransit services mature, agencies increasingly face decisions about whether to expand, modify, or discontinue microtransit services—and how to allocate scarce operating funds across competing transit priorities.Despite growing investment, there is no consistent approach to measuring whether microtransit services are delivering meaningful benefits relative to their costs, or whether those benefits are equitably distributed. Without clear and well-balanced performance metrics, agencies risk drawing the wrong conclusions about success or failure.
published journal article
What Is the Connection? Understanding Shared Micromobility Links to Rail Public Transit Systems in Major California Cities
Sustainability
Publication Date
January 9, 2024
Associated Project
Author(s)
Mengying Ju, Elliot Martin, Susan Shaheen
Areas of Expertise
Abstract
As shared micromobility (bikes and scooters) has proliferated throughout urban areas, there has been growing interest in how it facilitates connections with rail transit systems. This study explores the magnitude of interactions between shared micromobility and rail public transit systems using shared micromobility trip data and rail transit schedule data. We evaluate over one million trips from October 2019 to February 2020 in four California cities (San Francisco, Los Angeles, Sacramento, and San Jose) and develop criteria to identify trips connecting to rail transit. These include spatial and temporal rules, such as whether a trip starts/terminates close to public transit stations and whether a trip takes place when transit systems are operating. The criteria are examined via sensitivity analyses. The results indicate the degree of interaction between rail public transit and shared micromobility varies across cities and systems (i.e., docked/dockless). Most connections take place in the downtown or around public transit hubs. About 5–20% of all shared micromobility trips are identified as accessing or egressing from rail transit. These connecting trips exhibit commute-driven patterns and greater measured velocities. We conclude by examining the applicability of incorporating schedule information into the identification process of shared micromobility trips connecting to rail transit systems.
Suggested Citation
Mengying Ju, Elliot Martin and Susan Shaheen (2024) “What Is the Connection? Understanding Shared Micromobility Links to Rail Public Transit Systems in Major California Cities”, Sustainability, 16(2), p. 555. Available at: 10.3390/su16020555.Related Publications
Phd Dissertation
Essays in urban economics
Publication Date
January 1, 2009
Author(s)
Areas of Expertise
Abstract
Three independent research papers, all broadly focused on urban and transportation economics comprise the chapters of this dissertation. These empirical papers address a variety of policy oriented issues surrounding the automobile. Although related in theme, the objective, scope, and empirical strategy of each paper differs. The first chapter, “Does traffic congestion reduce employment growth?”, examines the impact of traffic congestion on employment growth in large U.S. metropolitan areas. I use an historic highway plan and political variables to serve as instruments for endogenous congestion. The results show that high initial levels of congestion dampen subsequent employment growth. This finding suggests that increasing the efficiency of public infrastructure can spur local economies. A set of counterfactual estimates show that the employment-growth returns from modest capacity expansion or congestion pricing are substantial. The second chapter, “Induced demand and rebound effects in road transport” (with Kenneth Small and Kurt Van Dender) uses a simultaneous equations model and aggregate data to estimate how drivers’ respond to exogenous increases in vehicle fuel-efficiency. One consequence of efficiency improvements is an increase vehicle use, which can moderate fuel savings. Accurate measures of this so-called ‘rebound effect’, are of interest to policy makers assessing the effectiveness of the Corporate Average Fuel Economy standards. This research paper also measures how traffic congestion and highway infrastructure affect vehicle use. The third chapter, “Evaluating the effectiveness of metered parking policy: evidence from a quasi-experiment”, uses a unique observational data set to assess metered parking policy. Although metered parking is ubiquitous, we know little about its effectiveness, particularly its impact on the retailers it is designed to assist. Sharp twice-daily changes in parking meter enforcement allow me to compare shopping behavior in both free and metered parking environments. Using the regression discontinuity design, I find that parking fees can have large impacts on nearby commerce.