First, the shops that local people can walk to could not survive if they relied exclusively on foot traffic. These problems would also be true of an suburban town center. If increased population density led to increased use of mass transit, as planners assume, then Portland should have seen a major increase in transit over the past twenty years. In fact, the share of trips using mass transit has declined from 4.1 percent in 1977 to 3.3 percent in 1994. This is not to say that the automobile is the perfect form of transportation.
Car drivers impose huge costs on others in the form of pollution, congestion, and safety.
The fact that drivers don't have to pay these costs is a major reason why cars seem more convenient than transit. The solution to these problems, however, is not planning or zoning but making people pay their full share of costs by, for example, charging fees for pollution emissions or rush hour highway tolls. It was the unplanned mixture of uses to which planners now want to return that led to demands for zoning in the first place. In 1920, no major U.S. city had a zoning ordinance. Architects and planners worried that inappropriate activities, such as factories and residences, were often located adjacent to one another.