On March 2, 2010 the U.S. Environmental Protection Agency (EPA) released a federal register notice officially announcing the release of MOVES2010 and its adoption by EPA as the standard emissions model for the development of State Implementation Plans (SIP) and regional transportation conformity analyses.

Appendix A of the Motor Vehicle Emissions Simulator (MOVES) 2010 User Guide recommends that emissions rates between speed bins be interpolated relative to the estimated speed used in the analysis and the average speed of the speed bins used in MOVES2010. The typical speed bin in MOVES2010 covers a range of five miles per hour centered on an average speed for the bin. The emission rate for any given bin is particularly associated with its average speed. Since the typical average bin speed is separated by five miles per hour from its nearest neighbor, the concern expressed in the user guide is that a marginal change in speed could move traffic into the next speed bin. This could result in emissions estimates that are overly sensitive to changes in speeds. The interpolation of rates is meant to make the shift in emissions relative to the actual shift in speed. The incorporation of speed bin interpolation increases the post-processor’s run time. The additional cost and effort involved with interpolating speed bin rates may not be worthwhile if the ultimate difference in emissions estimates turns out to be marginal; however, a significant difference to emissions estimates could make this interpolation a critical aspect of the air quality modeling process.

This presentation uses an air quality post-processor developed for the Indiana Department of Transportation with travel demand model data from MPOs within Indiana to test the implications of applying or not applying speed bin interpolation. The post-processor along with all of the MOVES2010 emissions rates used for this study have gone through a rigorous interagency consultation group process and are currently accepted in Indiana for the development of SIPs. The presentation covers background on mobile source emissions modeling, detail on the logic of speed bin interpolation, and a review of the findings of the analysis.