Urban sprawl and public health.

When regular steam ferry service between Brooklyn and Manhattan began in 1814, the first commuter suburb became possible. 1 Suburbs continued to develop slowly but steadily during the 19th and early 20th centuries, thanks to transportation advances such as commuter trains and streetcars, the innovations of early real estate developers, and the urge to live in pastoral tranquility rather than in urban squalor. As automobile ownership became widespread starting in the 1920s, suburban growth continued, a trend that accelerated greatly during the second half of the 20th century. One in two Americans now lives in the suburbs. 2 In recent years, the rapid expansion of metropolitan areas has been termed " urban sprawl " —referring to a complex pattern of land use, transportation, and social and economic development. As cities extend into rural areas, large tracts of land are developed in a " leapfrog, " low-density pattern. Different land uses— housing, retail stores, offices, industry, recreational facilities, and public spaces such as parks—are kept separate from each other, with the separation enforced by both custom and zoning laws. Extensive roads need to be constructed; for suburban dwellers, most trips, even to buy a newspaper or a quart of milk, require driving a car. Newly built suburbs are relatively homogeneous in both human and architectural terms, compared with the diversity found in traditional urban or small town settings. With the expansion of suburbs, capital investment and economic opportunity shift from the center to the periphery. Regional planning and coordination are relatively weak. Clearly, the move to the suburbs reflects a lifestyle preference shared by many Ameri-cans. Such a major shift in the nation's de