Clear, accessible definitions for common urban planning terms.
What Is an Urban Growth Boundary?
Some cities and regions limit the growth of sprawl by setting an urban growth boundary—a strict geographic limit on where real estate development can occur.
Urban growth boundaries are geographical limits for sprawling development around a city, county, or region. Development is permitted inside the urban growth boundary; agricultural land and natural space is protected outside the urban growth boundary. Urban growth boundaries are sometimes also called urban limit lines, urban development boundaries, or greenbelts, varying by jurisdiction.
Urban growth boundaries (UGBs) are designed to protect natural and agricultural lands by preventing greenfield development, or real estate development in previously undeveloped areas. Most UGB laws allow regions and cities to expand the UGB through a public vote or through legislation when it's deemed necessary.
Sometimes, governments pair urban growth boundaries with designated growth areas or urban growth areas—land targeted for development by investments in infrastructure (e.g., roads and sewers), development incentives (e.g., tax breaks or by-right permitting), land-use regulations (e.g., permissible building and zoning codes), and land acquisitions, among other actions.
While on the one hand, an urban growth boundary presents a clear obstacle to development on the fringe, on the other hand, they can serve as an incentive for development by making it easier and quicker for projects inside the urban growth boundary.
The decision to set UGBs as well as the decision to expand UGBs once they are in place can be politically contentious processes. As we'll see in more detail below, the consequences of UGBs—on sprawl, density, and the affordability of housing—are also a subject of ongoing research and debate.
Oregon: Urban Growth Boundary Trail Blazers
The idea of urban growth boundaries (UGBs) originates in the U.K. in the early 20th century—first outside of London and then for the entire country. In the United States, Senate Bill 100 in Oregon was the first law to mandate UGBs in response to concerns about sprawling development overwhelming natural landscapes and rural communities.
Under Senate Bill 100, Oregon required every city and county in the state to define a UGB as part of a state-required comprehensive land use plan. Other states soon followed Oregon's model, including Washington State, with the Growth Management Act of 1990, which required UGBs for the state's more urban counties.
California requires each county to have a Local Agency Formation Commission, which sets urban growth boundaries for each city and town in the county.
Since Oregon first adopted its requirement, numerous U.S. jurisdictions have adopted UGBs, including the cities of Boulder, Colorado; Honolulu, Hawaii; Virginia Beach, Virginia; Lexington, Kentucky; Knoxville, Tennessee; and San Jose, California. Entire regions, namely Miami-Dade County, Florida and the Minneapolis–Saint Paul metropolitan area of Minnesota, have also instituted UGBs.
Where UGBs cover multiple jurisdictions, like in the Twin Cities region, a regional urban planning power is frequently empowered by the state or regional government to manage the boundary. The same use of regional planning power is at work in Portland, Oregon as well. Every six years, the Metro Council, the metropolitan planning organization, or MPO, must prepare an Urban Growth Report to assess the existing supply of land. In the Urban Growth Report, the Metro Council forecasts population and employment growth in the region for the next 20 years and proposes adjustments to the region's UGB as necessary to meet that forecasted growth.
Why, or Why Not, Urban Growth Boundaries?
With so much development potential (along with the tax revenues and economic activity that result from development) and critical natural resources at stake, urban growth boundaries (UGBs) create almost constant controversy, but especially whenever housing prices rise. In most parts of the country and many in the world, sprawling, horizontal development on the fringe of metropolitan areas is the preferred approach to housing a growing population. Urban growth boundaries create an obvious obstacle to the unrestrained development of land considered by some to be a hallmark of the U.S. system of property rights.
Opponents list numerous negative outcomes as consequences of UGBs, like increased housing prices and housing density in developed areas, as well as a lack of housing options available for the middle class.
Proponents argue that suburban living comes with extra costs that aren't considered when only factoring in the relative cost of housing on the edge of regions (such as additional transportation costs for residents and extra infrastructure costs for local and regional governments).
Some proponents will instead focus on the pressure created by UGBs for cities and regions to use "smart growth" planning strategies that accommodate growth with dense, mixed-use development in walkable neighborhoods, in addition to a well developed public transit system for longer trips within the urban area. Proponents argue that UGBs revitalize city centers by closing the pressure release valve of suburban sprawl that many regions differ to as the status quo.
Proponents also call attention to the environmental benefits of urban growth boundaries from protection of farmland, forests, natural areas, and open spaces around the edges of metropolitan areas. Urban growth boundaries are also credited with reducing greenhouse gas emissions and other effects of the automobile trips enabled by sprawl, like additional air and water pollution, while creating other environmental risks, like wildfire.
Since Oregon adopted Senate Bill 100, researchers have found conflicting evidence on either side of the debate. According to research that attracted media coverage in 2017, residential population leaves the Portland region, beyond the limits of the UGB in nearby counties in Washington, rendering the UGB ineffective as a deterrent of sprawl.
In another study from 2006, researchers found that developed areas of Knoxville, Tennessee, since the implementation of a UGB. Also in the favor of proponents, the same researcher that found the Portland region's UGB did not slow sprawl also found that the UGB did not significantly increase housing prices.
Another case for UGBs has been made in the wake of wildfires in Northern California in 2017—an environmental risk predicted to occur more frequently as a consequence of climate change and as sprawl expands farther into the wildland-urban interface, where wildfires can threaten the built environment. According to reports, firefighters were able to protect the city's of Windsor and Healdsburg, well defined by UGBs. The city of Paradise, California, destroyed by the Camp Fire in 2018, is using greenbelts as a resilience strategy to prevent similar disasters in the future.