Uncontrolled urban growth is probably the greatest obstacle to sustainable development in the United States. Cities are spreading over the natural landscape far faster than population increases or economic progress require, while older urban districts with their valuable infrastructures are underused or abandoned.
The design of new buildings can enhance sustainability; but a new colony of earth-sheltered, solar houses out on the suburban fringe is far more harmful to the environment than the same number of new, conventional houses on an existing street within an established community. Building on untouched sites always destabilizes natural systems and can mean losing valuable agricultural or forest land. Access to the new development requires more roads, more trips, more extensions of the urban infrastructure; in other words, more natural resources used and more pollution created.
Despite a generation's experience with increasingly detailed federal and state environmental legislation, most urban growth is still out of control. The environmental impact statement has undoubtedly made new projects more responsive to environmental concerns, but the review process is cumbersome and applies only to major developments. Coastal zone management and stricter air- and water-quality standards have helped save sensitive dunes and wetlands, brought rivers back to life, and reduced smog. But rapid growth continues to create new environmental problems.
Most development is still the result of thousands of local decisions made by individual communities about separate projects. Development regulations in the U. S. have traditionally been delegated by the states to local government, and home rule on development issues is strongly established and unlikely to change. Private real-estate investments in separate, competing developments have been the prime mechanism for urban growth; that is not likely to change either.
Sustainable development is nevertheless possible. It requires four policy innovations that are well within the existing powers of states and local government; and there are current prototypes for each course of action. Taken together and combined with existing environmental legislation, they would add up to successful regional growth management and local design.
1. Laws establishing growth limits around existing cities and relating new development to the availability of infrastructure and public facilities.
2. Local zoning that ties development directly to the carrying capacity of the natural landscape and environment.
3. Public policies that make the creation of communities the primary objective of development regulation.
4. Restoration of natural landscapes in by-passed and derelict urban areas, and other policies to restore vitality to older cities.
Growth Boundaries and Concurrency
Growth boundaries clearly separating land that may one day be urbanized from land that is expected to remain rural are the essential first step in achieving sustainable development. Without the boundary there is a continual tendency for urbanization to leapfrog outwards, seeking cheaper land prices, fewer rigorous regulations, and less community opposition. Without growth boundaries, zoning ordinances establish theoretical development potential far in excess of what is actually needed, property taxes rise according to the zoning, and banks lend money based on what the land might be worth in the future and not on current use.
If there were less abandonment of existing cities, if more new investment went into bypassed parts of already urbanized areas, if new development were in "pedestrian pockets" or other kinds of planned communities compact enough to be served by rapid transit, then even less new land would be needed.
While development regulation is a local issue, the power to make the regulations comes from the state and, as urban regions become larger and larger, the state needs to play a stronger role as the ringmaster for local decisions.
Oregon has had state planning legislation since 1973. The law requires each community to evaluate potential economic development and community needs and then draw a growth boundary around each city. Funds for highways, transit, public facilities, and infrastructure are targeted to areas within the growth boundaries. This kind of planning is not easy. It took until 1986 for all communities in Oregon to draw up plans that met state-planning-agency standards.
Growth boundaries are not the only method of limiting urbanization. Florida relies on the principle of concurrency: that is development should not be approved in new areas unless it is supported by roads, utilities, and public facilities constructed on the same schedule. One problem with concurrency is that it tends to push commercial development outward from existing centers because of estimates of increased traffic congestion, even when the real remedy for traffic problems would be greater centralization of offices and retail centers in already urbanized areas.
Concurrency can also promote the extension of existing utility systems into sensitive landscapes that would better be passed over. Using both concurrency and growth boundaries, as Washington state does, makes each policy more effective, as the state can establish limits to development and also moderate the pace of new construction.
But growth boundaries and concurrency are general guidelines that say little about the quality of what is built within or outside the limits they establish. More detailed growth management requires environmental zoning.
Environmental Zoning
Most local zoning codes assume a billiard table surface as the ideal for a development site, a concept that comes from defining land primarily as a commodity and not an ecosystem. Subdivision ordinances frequently mandate regarding to bring the actual land closer to the billiard-table ideal and that, in turn, requires stripping all existing vegetation. To preserve the ecosystem, a different approach is needed. A generation ago Ian McHarg in Design with Nature outlined a method of classifying land according to its carrying capacity for new development. Land judged to be the least subject to environmental constraints would be the best place to build. Lane Kendig in his book, Performance Zoning, shows how to take the kind of environmental analysis McHarg advocates and apply it to zoning.
Most zoning codes relate development density to land area. Kendig outlines a system of discounting land areas based on the sensitivity of the land to disturbance during development. For example, a portion of the site that is actually under water would be discounted 100 percent, shoreline areas 75 percent, mature woodlands 85 percent, slopes of 15 degrees or greater 70 percent, and so on.
Making these discounts an amendment to a zoning text can reduce development density in environmentally sensitive areas without controversial changes to the current zoning map or community-financed site surveys that determine precisely where the sensitive areas are located. A developer applying for a building permit must present, as part of the application, a site map showing all natural features, with contours described at two-foot intervals. Areas of environmental sensitivity are computed, discounted, and the zoning densities adjusted accordingly.
Environmental zoning works best in association with planned-unit-development ordinances that permit buildings to be clustered in the most buildable areas of the property. Planned-unit development in turn works best in association with environmental zoning, which prevents excessive densities being transferred to the portions of the site most suitable for new construction.
Regulations That Create Communities
Even after development has been confined by growth boundaries, and modified by environmental discounts, successful growth management requires communities to amend zoning and subdivision ordinances to permit affirmative decisions about where and how development should take place.
When zoning and subdivision prototypes were created in the 1920s, they were intended to govern relatively small additions to existing cities and towns. These regulations were never meant to be the sole control over development of hundreds or thousands of acres; and they don't work at this scale. Blanketing the countryside with single-family-house districts and mapping endless strip-commercial zones along highways is the formula for urban sprawl. Environmental zoning can make existing ordinances more responsive to the ecosystem, but, by reducing densities, they can spread out development even more.
Using already-built communities as the armature for new development within growth boundaries is one zoning strategy. When new communities are planned, they should be located only in places which are environmentally suitable for new construction and have good transportation access.
Since conventional zoning and subdivision by themselves will not create a community, new kinds of development regulation are needed.
Andres Duany and Elizabeth Plater-Zyberk have used their experience in planning new towns, including the well-known resort, Seaside, to draft an alternative to conventional large-scale or planned-unit-development zoning provisions for Dade County, Florida. This new rule book, called a '`Traditional Neighborhood Development District Ordinance," is intended to create neighborhoods instead of tracts and includes provisions that ordinarily appear in both zoning and subdivision ordinances.
Neighborhoods must be no smaller than 40 acres and no larger than 200. Larger developments must contain multiple neighborhoods. Within each neighborhood there must be a mix of residences, shops, workplaces, and civic buildings. There are rules about squares and parks, the street organization, and the size and arrangement of blocks. There are rules about sizing streets, and about the character and placement of buildings. Another model is Sacramento County's Transit Oriented Development Design Guidelines, prepared by Calthorpe Associates in association with Mintier and Associates, which seek to create centralized community districts that are dense enough to support some kind of rapid transit. Such ordinances apply primarily to new development; there is also the whole task of restoring or creating neighborhoods in already developed areas or in fragmented, partially built-up commercial districts.
The State of California authorizes local governments to prepare Specific Plans. These provisions had been in the state code since 1965, attracting little attention until some amendments were made in 1980 that made the specific plan even more effective in repairing faulty zoning and development patterns. Among the 1980 amendments: an exemption from environmental-impact statement requirements for any development within the specific plan, as the plan itself must have an impact statement.
A specific plan is like a planned-unit development in that an individual design can become the zoning. It differs from planned-unit development in that it can apply to any number of property owners, can be prepared on a community's initiative, and — like a zoning ordinance — does not require the consent of the owners involved. Specific plans also resemble urban-renewal plans, but there is no need to make findings of blight or deterioration, nor for government to acquire any of the property. A local authority that has designated an area for a specific plan can assess the property owners within the designated area for the costs of preparing the plan.
This powerful planning mechanism is not as controversial as might be expected because it also provides benefits for property owners. Instead of playing zoning as a game with winners and losers, property owners can pool their advantages and attract development that none could have hoped for individually.
Restoring the Natural Environment
The Mystic River near Boston and is typical of riverfront land in older American cities where derelict industrial sites — mostly built on fill dredged out of the river and harbor — are sliced by expressways. When Carol Johnson & Associates was retained to turn this area into parkland, much of the soil was toxic to plants. The ground was turned into a growing medium by blending layers of clay, silt, sand, and peat, without importing topsoil stripped from other locations.
In the first stage, 80 acres were redeveloped at a cost of $5 million. The transformation of the riverfront gives houses in an urban Somerville neighborhood a setting comparable to choice locations much farther out in suburbia, while the park itself is an amenity rarely found in close-in urban neighborhoods.
Many depressed areas of older cities have been blighted by physical factors: railway and highway viaducts, exposed electrical substations, derelict industrial land. Highway departments routinely build landscaped noise barriers along highways in suburban communities; no such investment is made in the inner city. It is difficult, if not impossible, to restore blighted urban areas that are in the acoustic shadow of a highway, up against a railway track, or along a polluted river edge lined with derelict industry. Areas that house only people who have no other option are the places likely to have the worst social problems. Without a mix of incomes, without people who have choices and a sense of control over their own future, there can be no community.
Reviving older parts of the metropolis requires more than just physical improvements. But if growth is to be limited at the urban fringe, desirable development locations need to be created within already urbanized areas. Barriers along viaducts can reduce noise and local effects of air pollution. The restoration of river-edge environments also helps restart natural systems, leading to improvements in air and water quality. The cost seems low for the benefits generated.
People who live on the rapidly developing fringe of a city, who are unmoved by the plight of the poor trapped in deteriorating urban neighborhoods, may be alarmed by the influx of new neighbors willing to endure long commutes to escape urban problems. Understanding that rural growth and urban deterioration are two parts of the same problem can help build a constituency for the big investments necessary to make up for decades of neglect of urban areas.
Of course the world's ecosystem is the product of many additional factors. Growth boundaries, environmental zoning, planned communities, and the restoration of derelict cityscapes will not by themselves create sustainable development. But there won't be sustainable development without them.
Some suggested reading that gives more detail about the complex interactions of environmental and planning issues:
1. Building Sustainable Communities, a series of 11 handbooks developed by the Global Cities Project in San Francisco. 415/771-3910.
2. Balanced Growth, A Planning Guide for Local Government, published by ICMA, the International City Managers Association. 202/289 4262.
3. Sustainable Cities, the proceedings of a 1992 conference, published by Eco-Home Media in Los Angeles. 213/662-5207.
Jonathan Barnett is professor of architecture and director of the Graduate Program in Urban Design at the City College of New York, and is also a consultant to several cities and suburban communities.
