A Simulation of the Effects of Transportation Demand Management Policies on Motor Vehicle Emissions

Increasingly, planners and policy analysts are paying significant attention to the interactions connecting transportation, land use and air quality in a metropolitan setting. These efforts are driven largely by transportation conformity, a Clean Air Act provision requiring both total emission budgets and mobile-source emission sub-budgets in nonattainment areas. All transportation plans in these areas must pass a conformity review to ensure that plan implementation over a 20-year planning horizon will not violate any emission budget in any year. Many nonattainment areas have adopted or have under consideration a set of transportation demand management (TDM) tools that can be adopted to earn emission "credits" toward meeting the transportation emission budget. These measures may include smart growth policies, which are aimed primarily at the supposedly inefficient use of land in suburban development and which are believed by many observers to reduce VMT and emissions as well. They may also include a variety of transportation policies designed to reduce if not completely internalize the congestion externality. In this paper we focus on the latter type of policies. We compare the emission-reducing properties of a number of transportation policies designed primarily to address congestion. The modeling platform we use is LUSTRE, a spatially detailed and behaviorally complex simulation of transportation, land use and economic activity in the Washington, DC region. LUSTRE also calculates an overall welfare measure that is consistent with utility theory, and we add that measure to the comparison.