Much of the recipe for urban sprawl can be found in local zoning and subdivision regulations. The endless ribbons of commercial development along highways all follow zoning and so do the big tracts of suburban houses, each the same size on the same-sized lots. The drastic stripping and bulldozing of the suburban landscape is often required by the subdivision ordinance.

Most U.S. land regulation is based on prototypes published by the U. S. Department of Commerce in the 1920s. Zoning and subdivision codes that have evolved from these early models do not deal appropriately with office parks and big-scale housing developments, or with modern retailing.

There are two basic problems with current zoning and subdivision laws: they treat land as a commodity and not an ecosystem, and they protect the neighbors from negative influences rather than creating a positive template for the whole community.

Protecting the environment

The subdivision ordinance, which regulates the division of tracts of land into building lots, can be a means of bringing environmental considerations into land-use policy. The ordinance can specify that there should be no changes to natural drainageways and steep hillsides, and it can require the developer to show how buildings will be kept away from sink holes, easily eroded soils and landforms or any flood plains and wetlands.

In addition, there can be retention that water should leave the property no faster after development than it did before. As most zoning codes base the amount of development permitted on the area of the lot, an amendment to local zoning can reduce the amount of environmentally sensitive land counted in the lot area for zoning purposes, bringing development into harmony with the carrying capacity of the landscape.

Building neighborhoods

But environmental protection by itself may just spread new construction more thinly. Zoning codes also have to promote neighborhoods instead of tracts, and towns instead of strips of commercial development along highways. Communities can add a neighborhood zone to their ordinance to permit different lot sizes within the same overall density, something that used to happen all the time before zoning but is now forbidden by most codes. Zoning maps can make commercial strips at key intersections into mixed-use zones, the equivalent of traditional town centers. And strip-commercial zoning can be phased out in favor of multi-family districts that relate to nearby neighborhoods instead of to the highway.

Here is a way to rebuild zoning and subdivision codes to meet modern conditions:

1. Enact a grading and tree-protection ordinance. Bulldozing the land and chopping down stands of mature trees should require a permit conditioned on an approved development plan. Agricultural activities and minor domestic changes in landscaping can be exempted in well-drafted ordinances.

2. Make environmental protection part of zoning and subdivision ordinances to safeguard such areas as steep slopes, natural drainageways and places with unstable subsoil conditions. Some localities will also want to subtract the most environmentally sensitive land from the density calculations.

3. Add a neighborhood category to the zoning ordinance. A neighborhood zone permits a mix of different lot and house sizes and allows for civic buildings and a percentage of shops and other services. It permits developers to propose communities instead of subdivisions.

4. Add specific plan districts to the zoning ordinance. The specific-plan procedure is for areas in multiple ownership. The plan becomes the zoning for the area. Where enabling legislation permits, it can be made compulsory; otherwise the owners have to agree on the plan. This measure is particularly useful for replanning commercial districts.

Jonathan Barnett, a professor of practice in city and regional planning, adapted this article from Planning for a New Century (Island Press), a book based on an interdisciplinary seminar at the University.

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