Cities have always expanded horizontally unless curbed by walls, natural barriers, or the inability to communicate over distance. Policies such as greenbelts or the exclusion of immigrants—the sixteenth- and seventeenth-century attempts to restrain the growth of London to exclude the poor, or the apartheid restrictions on black immigration—have not been able to maintain themselves over time. Recent urban policies have included either allowing low-density suburban expansion, building dense public housing on the periphery, establishing new towns, or allowing poor immigrants to squat in minimally controlled settlements.
American cities have chosen the first of these models. The suburbs in the early years of the twentieth century were made up of large lots and made possible by the invention of the telephone and pre-automobile street-cars. Before World War II, less than half the nation owned their homes and less than half the housing stock was in single-family homes. After the war, the percentage of families owning their homes jumped from nearly 40% in 1940 to 60% in 1960 due to higher incomes, the federal highway program, tax incentives for home ownership as a stabilizing social force, FHA and VA financing, and other factors. Levittown built 150 standard 25 ft x 30 ft cottages a week, each costing $7,900, requiring, with a government-subsidized loan, a monthly payment of $58 for 25 years. These suburbs attracted the planned shopping center, an architecturally unified development with large amounts of off-street parking. Today megamalls offer the shopping experience as a new form of entertainment and have become so large that pedestrians cannot cover them in a day. Suburban growth has broken the link between city center and its outskirts: in 1975, people who commuted from home to work in the suburbs outnumbered people who commuted to the central city by almost two to one. Outlying suburbs, now called "urban villages" or "edge cities,", are more diverse in land use, have larger houses (in 2000 the American house averaged over 2,000 square feet, twice as large as it was in 1970), and have become different cultural enterprises than the post-World War II suburbs: "a ranch-style tract house, a Chevrolet, and meat loaf for dinner will not do anymore as the symbols of a realized dream." The regional suburban city, in which people are able to cover very large distances, depends entirely on private automobiles. Private automobile traffic continues to increase, from 1.03 billion miles in 1970 to 1.49 in 1987, and road space over the same time decreased from 61 yards per vehicle to only 39. While the new cars are cleaner, the condition of the air is worse, in part because of the increase in car use.
Recently the large American low-density metropolis has been subject to growing criticism of its uncontrolled growth, now called "sprawl," a relatively undefined word, as "slums" were in the late nineteenth century. The economic wastefulness and ecological damage of "sprawl" has led to recent attempts to control or balance the growth of metropolitan areas. So, exacting impact fees on growth on the outside edge, marketing higher densities on smaller lots, calling for increased light-rail systems, land-banking open space and stimulating small-scale farming, are among the more common policies. Portland, Minneapolis and Vancouver have become some of the metropolitan governments to invoke "smart" growth. But the model of creating new growth points at radial train line stops to increase public transportation and develop new nodes has not proven in practice to be as appealing as in theory; this is one of the models of good metropolitan form which will need greater study in the future. There is also little attention to achieving greater social equity, surely a major attribute of any "good" city, through these spatial policies. Among practices which set out to reform American low-density development are those of the highly publicized "new urbanism." This practice has been unable to deal with fundamental issues such as decreasing automobile use or creating greater social equity despite some largely theoretical advocacy of higher densities and light-rail transportation, which the densities of American suburbs are incapable of supporting. This work has almost exclusively focused on methods of improving the micro-environments of developers' suburbs. The American downtown, on the other hand, has, with few exceptions, increased in population over the past two decades. It has become more diverse with a population that is made up largely of non-family residents, who have few children (only 17% of those living in downtowns are under 20) and rent housing at twice the rate of residents in the metropolitan area. There are many reasons given for this rebirth, among which is a theory of homeostasis in which external growth in living organisms like cities is balanced by internal growth.
Sennett, Richard. "The Space of Democracy." Harvard Design Magazine, Summer 1999.
Beinart, Julian. "Keeping Post Office Square as a Public Trust." The Boston Globe, June 6, 1984.