U.S. Cities Find Right Sizes for Their Greenbelts

The idea of an urban growth boundary (UGB) is simple: draw a line around a city, restrict development outside that line, and promote development inside that line. Cities grow more compact, and the outlying areas, whether they are used for agriculture or conservation, remain open and green. Simple as it is, some UGB's aren't worth the paper they're drawn on. 

A session at the recent American Planning Association conference in Seattle analyzed the implementation of UGB's in three American cities: Portland, Oregon; King County (Seattle), Washington; and Denver, Colorado. Panelists agreed that the success of a UGB depends not on simply drawing a line but rather on sustained political support for the boundary and for the development patterns needed to complement the boundary. In some cities, weak political support leads to changing boundaries and renegotiations that render UGB's almost useless.

Some highlights: 

• Portland: Since the UGB was created in 1979, "the population of Portland has grown 60 percent, while the urban growth boundary has expanded just 14 percent." Despite an expected addition of 200,000 homes to the area by 2035, the city does not currently expect to expand its boundary.
• King County: "In 1990, there was a bipartisan agreement that led to the growth management act, which down-zoned two-thirds of the county from development areas to rural land, agriculture, and forests....98 percent of growth has been in the urban growth boundary." Rural landowners can transfer development rights to cities (but not vice-versa) to further encourage growth within the boundary. 
• Denver: The UGB of the Denver area has grown from encompassing 750 to 921 square miles since its inception in 1997. Cities "self-certify" their participation in the UGB plan, meaning that it relies on "peer pressure" to promote compact development.