Book excerpt: "Urban mobility is rapidly evolving in the United States, particularly since the introduction of app-based transportation network companies (TNCs) such as Uber and Lyft. As these services become more widespread, many have begun to question what effect they are having on the cities where they operate, including on public transit ridership, single occupancy vehicle trips and traffic congestion. In the face of widespread declines in public transit ridership after a decade or more of growth nationally, these questions have become especially pressing. Speculation has grown around whether TNCs are leading to real changes in how people use public transit and private automobiles, or if these fluctuations are caused by other factors"--Summary.