When private developers select new housing sites, they seek cheap land that can easily be prepared for construction. This land is often not contiguous to the existing built-up area. Sprawl is the development of suburbs at relatively low density and at locations that are not contiguous to the existing built-up area. Sprawl is also fostered by the desire of some families to own large tracts of land.

Land is not transformed immediately from farms to housing developments. Instead, developers buy farms for future construction of houses by individual builders. The peripheries of U.S. cities look like Swiss cheese, with pockets of development and gaps of open space (Figure 13-52).

Suburban Sprawl

Albuquerque, New Mexico.

Sprawl incurs costs:

• Local authorities must spend more money extending roads and utilities to connect developments not contiguous to existing built-up areas.

• More agricultural land is lost through construction of isolated housing developments. More energy is expended because trips to work and services must cover longer distances.

Density Gradient

As you travel outward from the center of a city, you can watch the decline in the density at which people live. Inner-city apartments or row houses may pack as many as 250 dwellings on a hectare of land (100 dwellings per acre). Older suburbs have larger row houses, semidetached houses, and individual houses on small lots, at a density of about 10 houses per hectare (4 houses per acre). A detached house typically sits on a lot of 0.25 to 0.5 hectares (0.6 to 1.2 acres) in new suburbs and a lot of 1 hectare or greater (2.5 acres) on the fringe of the built-up area.

This density change in an urban area is called the density gradient. According to the density gradient, the number of houses per unit of land diminishes as distance from the center city increases. Two changes have affected the density gradient in recent years:

• Fewer people living in the center. The density gradient thus has a gap in the center, where few live.

• Fewer differences in density within urban areas. The number of people living on a hectare of land has decreased in the central residential areas through population decline and abandonment of old housing. At the same time, density has increased on the periphery through construction of apartment and town-house projects and diffusion of suburbs across a larger area.

Density Gradient in Cleveland, 1900-2010

The red line shows the current City of Cleveland boundary.

These two changes flatten the density gradient and reduce the extremes of density between inner and outer areas traditionally found within cities.

U.S. & U.K. Suburbs

The supply of land for the construction of new housing is more severely restricted in European urban areas than in the United States. Officials try to limit sprawl by designating areas of mandatory open space. For example, several British cities are surrounded by greenbelts, or rings of open space. New housing is built either in older suburbs inside the greenbelts or in planned extensions to small towns and new towns beyond the greenbelts. On the other hand, restriction of the supply of land on the urban periphery has driven up house prices in Europe.

Suburban Development Patterns in the U.S. and U.K.

(a) The United States has much more sprawl than the United Kingdom, through construction of discontinuous suburbs. (b) In the United Kingdom, new housing is more likely to be concentrated in new towns or planned extensions of existing towns.

Harlow New Town, United Kingdom

Smart Growth

Several U.S. states have taken steps to curb suburban growth. The goal is to produce a pattern of compact and contiguous development and protect rural land for agriculture, recreation, and wildlife. Legislation and regulations to limit suburban growth and preserve farmland has been called smart growth. Oregon and Tennessee have defined growth boundaries within which new development must occur. Cities like Portland, Oregon, can annex only lands that have been included in the urban growth areas. New Jersey, Rhode Island, and Washington were also early leaders in enacting strong state-level smart-growth initiatives. Maryland’s smart-growth law discourages the state from funding new highways and other projects that would extend suburban sprawl and destroy farmland. State development money must be allocated to “fill in” already urbanized areas.

Portland, Oregon, Urban Growth Boundary

New developments must take place inside the boundary.

Portland Urban Growth Boundary and Mount Hood

Pause & Reflect 13.3.2

How might urban growth boundaries help to slow suburban growth?