What about cars is bad? In turn, what should transportation planners do? In the early years of the automobile era, the transportation planner’s job was to develop street and highway networks. Sometimes the thinking was as simple as drawing lines on a map to connect concentrations of trip origins and trip destinations, and then building highways along the path that most closely corresponded to those lines. Air quality problems were not conclusively linked to automobile travel until the 1950s. Issues such as the displacement of persons from residential neighborhoods and the impact on habitat were secondary concerns at best until the 1960s. The primary, almost exclusive, focus during the first decades of the automobile era was to build a street and highway network that could accommodate a new mode of transportation. This began to change by the late 1960s. Planned highway networks neared completion in many cities. At the same time, the broader social costs of transportation became more apparent. Automobile emissions are a major contributor to urban air pollution. Traffic congestion has been a perpetual problem for several decades in most cities. Neighborhoods severed by highway projects often quickly deteriorated. Scholars and policy analysts now ask whether transportation resources are fairly distributed across different segments of society and how transportation access is linked to labor market success. As all of these issues have moved to the fore, transportation planning has increasingly focused on how to manage the social implications of transportation projects. Modern transportation planning now necessarily focuses as much on managing the social costs of travel as on facilitating travel. Because 87 percent of all trips in the United States in 1990 were by private vehicle (mostly cars and light trucks), the social costs of travel are, first and foremost, the social costs of the automobile. Public concerns regarding air quality, congestion, neighborhood stability, and equity gave rise to new regulatory agencies, technological innovations, and legal frameworks for transportation planning. Yet the demand for cleaner, less congested, more fair transportation systems persists. This is the context for the new urban designs. They seek, in large part, to address the social costs of automobile travel.
An inter-comparison of the social costs of air quality from reduced-complexity models