Author
María Arquero de Alarcón, with Jonathan Levine, Moira Zellner, and Yoram Shiftan 

Transit in the United States often suffers from the problem of inability to deliver travelers all the way from their point of origin to their destination. This “last-mile” problem is thought to deter transit use among riders with auto access, even when high quality transit service is provided for the majority of the trip distance. This study explores how transportation improvements, including automated driverless shuttles between origins of trips and nearby transit stations, and physical improvements enhancing pedestrians’ and cyclists’ commute might help overcome the last-mile problem particularly as they interact with policy shifts including changing in parking and fuel costs. To conduct this study, the authors developed an agent-based model representing the commuters and their preferences for different aspects of transportation disutility, namely cost, time and safety. Commuters in the model assess their transportation options in light of their preferences, the characteristics of their environment, and the various modes available to them. The model is calibrated with data from four Chicago neighborhoods, representing four different combinations of land-use patterns and household income. Simulations suggest significant potential for the combined shuttles and urban design improvements to shift downtown commuters to non-automotive modes (between 12 and 21 percentage point reduction in driving in three out of four neighborhoods). Less dense neighborhoods were more sensitive to higher parking costs, streetscape improvements and shuttle service than the denser and more pedestrian-oriented neighborhoods. Distance from the station encouraged driving, but the presence of shuttles encouraged shifts towards transit. Streetscape improvements tended to support transit use closer to train stations. In addition to anticipating a range of likely mode choice outcomes, the agent-based modeling approach facilitates exploration of the mechanism underlying travelers’ behavior. Rather than modeling through data fitting, this approach involved formulating theory of behavior first, using data to parameterize the conceptual model, and running simulations to see how the outputs would match observations. When discrepancies arose, the authors advanced the theory and reformulated the conceptual model to explain them. In this way, the authors found that a dense bus service shuttling travelers towards the commuter train station with express service downtown was critical in encouraging transit use, and extensive bus coverage throughout another neighborhood encouraged bus use to access downtown. Bike penalties representing various difficulties inherent to this mode (e.g., lack of physical fitness, the need for showering facilities at the destination, etc.) needed to be adjusted to higher values than those typically found in the literature, suggesting greater barriers to biking in this metropolitan area. Finally, the authors had hypothesized that pedestrian and biker presence would represent an important feedback promoting shifts away from driving, but this was not the case. Further in-depth empirical research is needed to improve the conceptual models of this feedback, and to understand how policy can leverage it to encourage greater transit, pedestrian and bicycle use.