Yonah Freemark, Neema Nassir, and Jinhua Zhao (2022). “Multimodal Relationships: Shared and Autonomous Vehicles and High-Capacity Public Transit.” In Shared Mobility and Automated Vehicles, edited by Ata Khan and Susan Shaheen. London: IET Books. 119-144.
Today’s urban transportation system does not function adequately for most of its users. Those who take transit are frequently beset by infrequent service, crowded trains, delayed buses, and inadequate coverage. Those who drive or are driven are stuck in traffic, contributing to climate change, and subject to the ever-present possibility of committing vehicular carnage. Those who walk or bike are confined to poorly maintained, often discontinuous, dangerous, and circuitous routes. Few receive the transportation services that adequately meet their needs, and some are excluded from the transportation system altogether due to their inability to pay, their age, or their physical abilities.
Part of the problem is that no mode, by itself, provides the capacity necessary to carry all people over all the necessary distances and with reasonable directness, which requires serving the full array of origins and destinations. Transportation network companies (TNCs), for example, offer direct door-to-door services but have limited capacity to carry large numbers of passengers; typical public transportation options, on the other hand, are high capacity but not direct. The introduction of autonomous vehicle (AV) technology, which we expect to be largely an extension of today’s private automobile and TNC system, will not by itself alter this dichotomous relationship. In Figure 7.1, we compare several of the key advantages of AVs and public transit. A transportation system that is made up primarily of these two modes would offer options that are demand responsive and offer economies of scale, respectively—but not both at the same time.
In this chapter, we consider the potential for a more integrated transportation system that merges access to services offered across modes in order to effectively bridge the gap between the three demands of capacity, directness, and distance, and that combines the respective advantages of AVs and transit as enumerated in Figure 7.1. Our examination specifically considers whether the advent of AV technology—particularly shared autonomous vehicles (SAVs)—can be used as a lever to enhance transit systems, not only by improving their efficiency, but also by filling the major gap that has limited transit’s success in attracting riders, especially in the United States: directness. Thus the fundamental motivation for our text is an effort to understand whether and how the transportation system can maintain the capacity benefits of transit (and thus its congestion-relieving and sustainable characteristics), while improving services to more people.