Linked simulation of land use and transportation systems: Developments and experience in the Puget sound region

Strategies to reduce motor vehicle travel by altering urban spatial structure are one piece of a comprehensive program to slow global warming. While the connections between urban spatial form and urban travel have long been recognized, there have been few attempts in the United States to model the interactions within the context of a public planning program in an urban region. One such effort, the Vision 2020 plan in the Seattle region, is described in this paper. The modeling tools utilized widely available travel and land-use models, applied interactively. A wide range of variables, consisting of transportation facility investments, demand management measures and land-use controls, were grouped into identifiable long-term alternatives. The analysis suggested some ambiguity in the ability to model the processes, particularly within a highly political planning program, and indicated rather modest effects of land-use changes on reducing urban travel over 20 to 30 years. Land use and demand management were most effective when supported by significant investment in facilities, including transit. Although attempting to alter urban spatial structure may not be the most cost-effective place to seek reductions in vehicular emissions over this period of time, planning programs like Seattle's may be an opportunity to mold less travel-dependent urban regions for the next century.