Abstract
This paper examines the impact of a regional simulation model on estimating vehicle emissions. The TRANSIMS software was used to simulate traffic for the Portland, Oregon, metropolitan area. Network and trip table data from the Portland METRO regional model were converted to TRANSIMS and calibrated against traffic counts. The TRANSIMS microsimulator was then used to generate detailed speed and volume information for 30-m link segments at 15-min intervals throughout the day. Second-by-second vehicle speeds were summarized with six speed bins (0, 16.8, 33.5, 50.3, 67.1, and 83.8 mph). The detailed simulation results were aggregated in various ways to produce the input data required by the MOBILE6 emission inventory software. MOBILE6 was also applied with specific parameters to test the impacts of various assumptions with regard to analysis year, seasons, vehicle types, facility types, and inspection and maintenance programs. The total emissions from each aggregation method were compared with the emissions estimated with the use of MOBILE6 with METRO's EMME/2 volumes and speeds. The analysis indicates that the emission estimates generated with simulation data are significantly different from the emission estimates produced by traditional modeling techniques. If simulation data are aggregated to levels that are more consistent with traditional regional outputs, the magnitude of the difference is minimized. In general, using the more detailed information produced by TRANSIMS or other simulation models will result in higher emissions than are currently estimated by using aggregate methods.
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