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
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.