Americans living in the fifty most congested cities spend an average of thirty-three hours each year stuck in traffic. Congestion causes much more than driver aggravation: air quality suffers, vehicle idling and stop-and-go traffic reduce fuel economy by as much as 30 percent, and we lose billions of dollars in productivity. These are the consequences as the automobile does what it is designed to do—transport a highly mobile population. Continued suburban expansion, reduction in household size, increase in number of workers per household, and general changes in lifestyle have all contributed to increased travel demand and greater congestion.

Even without congestion, from the perspective of capital utilization and energy consumption, automobile and roadway use is inefficient. First, the majority of personal transportation energy is consumed in moving personal vehicles that contain only one occupant and drive one or two hours a day. Second...