Handy, Susan L., Patricia L. Mokhtarian, Theodore J. Buehler, Xinyu Cao (2004) Residential Location Choice and Travel Behavior: Implications for Air Quality. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-04-48
The sprawling patterns of land development common to metropolitan areas of the United States have been blamed for high levels of automobile travel, and thus for air quality problems. The defining characteristics of “sprawl” include: low-density development, unlimited outward expansion, and “leapfrog” development (Burchell et al., 2002: 39). Most metropolitan areas in the United States are growing faster in land area than in population. Between 1982 and 1997, urbanized land increased by 47%, while population grew by only 17% (Fulton et al., 2001). This low-density pattern of growth has two important effects on travel, namely longer trip distances and greater reliance on the car. Although the causes of sprawl are complex, public policies have clearly played a role. The development of extensive freeway systems in metropolitan areas, which began in the 1950s, reduced travel costs and enabled suburban growth. Land-use policies, particularly conventional zoning practices, have also contributed to sprawl by requiring the separation of land uses and by restricting the density of development.