Average speed is an essential input to the air quality analysis model MOBILE6 for emission factor calculation. Traditionally, speed is obtained from travel demand models. However, such models are not usually calibrated to speeds. Furthermore, for rural areas where such models are not available, there has not been a reliable method for estimating speed.

In this study, a procedure was developed based on the Highway Economic Requirement System (HERS) speed model to estimate average speed using as input various data such as roadway characteristics and traffic conditions. This procedure was coded in MS Excel macro and can be attached to a workbook that contains the roadway inventory data in the HPMS format.

The comparison between the measured speeds and those estimated by the model demonstrated the strong performance of the model. The data availability and accuracy issue during the implementation stage was discussed.

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