Mass transit systems transport large numbers of people simultaneously in single vehicles. Examples of mass transit systems include buses, ferries, rapid rail, light rail, commuter rail and intercity rail systems. Although popular before the age of the automobile, mass transit systems have become marginal transportation modes in many cities in the United States. Recently however, as the negative impacts of automobile use have become of greater public concern, a renewed interest in encouraging mass transit has emerged. The Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 explicitly allocated funds toward improving mass transit systems.

Transportation congestion is worsening in the United States. In addition to the opportunity costs of time associated with traffic congestion, there are environmental costs associated with automobile use: emission of greenhouse gases, air pollution, noise pollution, and increased suburban sprawl and land use. Other social costs include increased probability of traffic accidents, increased...