University of Vermont Transportation Research Center

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In June 2012, the Environmental Protection Agency (EPA) released the “Operating Mode Distribution Generator” (OMDG) a tool for developing an operating mode distribution as an input to the Motor Vehicle Emissions Simulator model (MOVES). The tool converts basic information about traffic operations – idle time, grade, and average speed – into an operating mode distribution. This tool is designed to make project-level analyses for CO and PM hot-spots easier to conduct with basic traffic activity data. This paper compares the operating mode distributions obtained from this tool with those measured on a vehicle instrumented with the Total On-Board Tailpipe Emissions Measurement System (TOTEMS). TOTEMS generates a wealth of data, including a vehicle’s speed, idle time, and link grade – all of the inputs necessary to run the OMDG. The comparison is made for 4 signalized intersections on an urban arterial in Burlington, Vermont. This analysis shows that the OMDG, when compared to 31 test runs of an instrumented vehicle, was more accurate under circumstances of no to low grade and higher congestion (higher stop time). Estimation inaccuracies are most critical for specific operating modes -- for CO under high VSP conditions; for PM10 under braking conditions (i.e. VSP <0). This investigation has developed a method for quantitatively evaluating tools designed to simplify a mobile emissions analysis. Future work will include the development of models for estimating operating modes of a traffic stream using traffic microsimulation and highlighting those parameters that are most critical to calibrate for obtaining an accurate operating mode distribution estimate.