Evaluating the cumulative impacts of a long range regional transportation plan: Particulate matter exposure, greenhouse gas emissions, and transportation system performance

Long range regional transportation plans (LRTPs) are typically evaluated with performance measures calculated for the first and final years of the planning period. We call this the endpoint modeling method. Planning periods span 20-30 or more years, and therefore the endpoint method can overlook important changes that occur during interim years as well as cumulative impacts. For example, the impact of GHG emissions accumulating in the atmosphere and chronic or deadly diseases caused by exposure to high concentrations of toxic vehicle emissions cannot be reversed by plans that only perform well in the distant future. In this study we evaluate the annual performance of a LRTP created for the Albuquerque, New Mexico metropolitan area over a 28-year period by modeling land-use, travel demand, vehicle emissions and emissions exposure using an incremental and highly integrated land-use and travel demand modeling method. We call this the annual modeling method. We find non-linear and sometimes complex changes in annual emission rates, pollution exposure and other performance measures, indicating that end of period performance metrics may not be robust indicators of average and overall plan performance, which we argue are important considerations. Furthermore, we find that the annual modeling method has a large effect on land-use, traffic and emission exposure forecasts. By the plan's final year, the annual modeling method forecasts greater population and employment, and correspondingly greater traffic congestion and air pollutant concentrations in the region's largest activity centers than the endpoint modeling method, which is used by most MPOs.