Road Ecology Center

Few would dispute that highway projects in the United States have had impacts on land use and local growth. Beginning in the 1950’s, the spreading interstate roadway system abruptly increased access to land and communities that had been relatively untouched by development. As transportation infrastructure has reached maturity, current projects are usually small improvements to existing roads, and the influence of transportation projects on local growth has become much less obvious. In 1990, the state of Washington became the seventh state to adopt a Growth Management Act as a prescription for controlling growth by affecting density, zoning, mixed uses, and development timing. Since enaction, GMA has accommodated growth rationally by emphasizing the compaction of residential and commercial development within Urban Growth Areas separated by areas zoned for limited development. The Maltby, Washington, UGA is typical of this GMA product. Facing increased congestion and public safety issues, the Washington State Department of Transportation recently developed plans to expand the capacity and two rural intersections of State Route 522, which transects the Maltby UGA. The GMA directs that state and local agencies develop transportation systems that complement land-use goals, and the question arose of whether the project would induce growth beyond that planned under GMA. If the project induces growth beyond that already planned, agencies are responsible to offset the potential for these indirect project effects to sensitive habitat and species. In order to assess indirect effects, an analysis must quantify the proportion of future (anticipated) development that is a result of the specific roadway improvement beyond what is already planned, or that is ascribable to the individual roadway section. WSDOT and the U.S. Fish and Wildlife Service conducted an exhaustive search of local planning commission files, interviews with relevant stakeholders, and information available through GIS databases to address the proportion of local growth attributable to the SR 522 project. The analysis provided estimates of future changes in Total Impervious Area and other environmental impacts based on GMA-based projections, but was not able to assign a percentage of these impacts to the current expansion project. Federal agencies concluded that the current project would not individually affect sensitive species and habitat. Long-term actions such as the gradual change from rural to urban land use patterns in Washington and other Growth Management states may incrementally degrade the environment of species sensitive to minor changes, but it is not possible to assign a percentage of that growth to an individual project or a project that upgrades an existing roadway.