published journal article
policy brief
Sales of plug-in electric vehicles (PEVs), which include battery electric vehicles (BEVs) and plugin hybrid electric vehicles (PHEVs), have grown substantially in recent years (Figure 1), but market growth will need to accelerate significantly to meet California’s target of 5 million zero emission vehicles by 2030.
published journal article
We use panel data to investigate the before-and-after impact of a new light rail transit line on active travel behavior. Participants were divided into a treatment group and a control group (residing ¡1/2 mile and ¿1/2 mile from a new light rail transit station, respectively). Self-reported walking (n = 204) and accelerometer-measured physical activity (n = 73) were obtained for both groups before and after the new light rail transit opened. This is the first application of an experimental-control group study design around light rail in California, and one of the first in the U.S. Our panel design provides an opportunity for stronger causal inference than is possible in the much more common study designs that use cross-sectional data. It also provides an opportunity to examine how an individual’s previous activity behavior influences the role that new light rail transit access plays in promoting active travel behavior. The results show that, when not controlling for subject’s before-opening walking or physical activity, there was no significant relationship between treatment group status and after -opening walking or physical activity. However, when controlling for an interaction between baseline walking physical activity and treatment group membership, we found that living within a half-mile of a transit station was associated with an increase in walking and physical activity for participants who previously had low walking and physical activity levels. The results were opposite for participants with previously high walking and physical activity levels. Future policy and research should consider the possibility that sedentary populations may be more responsive to new transit investments, and more targeted “soft” approaches in transit service would be needed to encourage people to make healthy travel choices. (C) 2016 Elsevier Ltd. All rights reserved.
Preprint Journal Article
The development of mobility-on-demand services, rich transportation data sources, and autonomous vehicles (AVs) creates significant opportunities for shared-use AV mobility services (SAMSs) to provide accessible and demand-responsive personal mobility. SAMS fleet operation involves multiple interrelated decisions, with a primary focus on efficiently fulfilling passenger ride requests with a high level of service quality. This paper focuses on improving the efficiency and service quality of a SAMS vehicle fleet via anticipatory repositioning of idle vehicles. The rebalancing problem is formulated as a Markov Decision Process, which we propose solving using an advantage actor critic (A2C) reinforcement learning-based method. The proposed approach learns a rebalancing policy that anticipates future demand and cooperates with an optimization-based assignment strategy. The approach allows for centralized repositioning decisions and can handle large vehicle fleets since the problem size does not change with the fleet size. Using New York City taxi data and an agent-based simulation tool, two versions of the A2C AV repositioning approach are tested. The first version, A2C-AVR(A), learns to anticipate future demand based on past observations, while the second, A2C-AVR(B), uses demand forecasts. The models are compared to an optimization-based rebalancing approach and show significant reduction in mean passenger waiting times, with a slightly increased percentage of empty fleet miles travelled. The experiments demonstrate the model’s ability to anticipate future demand and its transferability to cases unseen at the training stage.
working paper
This paper describes the development and implementation of an agent-based activity microsimulation kernel based upon the concept that human activity is the negotiated interaction of socially and physically situated individuals and organizations. The kernel uses a modification of the contract-net protocol from the distributed artificial intelligence literature to represent the “physics” of interaction in human activity settings. The details of the kernel design and implementation are discussed.
published journal article
book/book chapter
published journal article
published journal article
research report
In California, there has been a growing concern about housing unaffordability and its negative consequences, but it has remained unclear how transportation is related to this issue. This report synthesizes the literature on the causes and consequences of local growth control which has been viewed as one of the most significant barriers to expanding housing supply and thus managing travel demand more effectively. Emphasis is on what insights can be gained from the literature and what further research is needed to better understand how transportation influences and is influenced by growth control actions.