Publication Detail

A Weighted Disaggregate Approach to Modeling Speed Correction Factors


Research Report

Suggested Citation:
Guensler, Randall L., Simon P. Washington, Daniel Sperling (1993) A Weighted Disaggregate Approach to Modeling Speed Correction Factors. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-93-06

Working within the constraints of California's existing speed correction factor (SCF) models, where average speed of emission testing cycle is the single independent variable, and four vehicle technology groups are used, we analyze an alternative disaggregate SCF modeling approach. The alternative model results in derived SCFs that better predict emission rates when compared to the existing modeling approach.

As an interim measure, we recommend that the disaggregate modeling technique developed in this paper be employed in estimating relationships between average speed and emissions. However, changing the analytical technique, or simply changing the regression model functional form and the resulting beta coefficients (as recommended in this paper) will not provide an adequate model. Neither the existing nor the recommended interim model, both of which employ average vehicle speed as the single explanatory variable, sufficiently nor convincingly explain the variation in emissions. Results indicate that additional data should be collected and that better models are needed. Ideally, these models will be based upon alternative functional forms and will include additional independent variables.