Between Politics and Planning: UrbanSim as a Support System for Metropolitan Planning

Overview There has often been an uneasy relationship between politics and planning in the selection of the policies and investments that shape urban areas. Competing interests vie to shape these decisions through the political process, while planning attempts to rationalize the process through analytical methods. Experience has shown that politics all too often trumps analysis, leaving both sides frustrated and the outcome poorly informed. The quest to elevate the political process through informed and objective analysis is a central objective of the development of planning support systems. This paper describes the recent development of UrbanSim, an urban simulation system, and its application as a planning support system for metropolitan land use and transportation planning. The need to promote consistency between land use, transportation, and air quality planning has motivated a substantially different approach to planning than characterized these efforts in previous decades. Transportation planning, perhaps through the 1970s, was preoccupied with reducing congestion through capacity increases. The secondary effects of transportation on land use, and the resulting induced congestion and consequent increase in emissions from the new expansion of capacity, had been well and widely documented (e.g., Downs, 1992). But these ideas did not impact the planning practice in most metropolitan areas until the passage of federal legislation mandating that these interactions be considered in transportation planning. In the early 1990s, The Sierra Club and Environmental Defense Fund lawsuit in the San Francisco Bay Area took on the