Vehicle Activity–Based Procedure for Estimating Emissions of Heavy-Duty Vehicles

Abstract

A new procedure for estimating the emissions of heavy-duty vehicles (HDVs) is presented. This procedure combines second-by-second data on actual in-use speed and acceleration of HDVs with data on average emissions rates of HDVs operating at corresponding speeds and acceleration rates. The initial implementation of this procedure used a limited amount of newly collected emissions data and a somewhat larger amount of previously collected HDV activity data. Validation tests provide a reasonable level of confidence about the validity of the nitrogen oxide (NO x ) emissions factors produced using this initial implementation. However, these tests also indicate that the small amount of emissions data used in the initial implementation is insufficient to produce meaningful estimates of emissions factors for carbon monoxide or particulate matter. The research, the procedure that was developed, the validation tests, the results for NO x emissions, and NO x speed correction factors derived from these results are briefly described. The speed correction factors are of particular interest. The minimum values for these factors occur at speeds higher than those currently used by the U.S. Environmental Protection Agency, and the factors grow more slowly at higher speeds than do the factors generated by MOBILE.