Predicting traffic volume growth rates resulting from changes in highway capacity and land development

The magnitude of potential highway user benefits and costs resulting from proposed highway improvements must be estimated with a reasonable degree of accuracy for highway agencies to make rational decisions in the public interest. The Highway Economic Evaluation Model (HEEM) has been developed for that purpose. One of the important aspects of the model is the assumed growth rate pattern which average daily traffic volume (ADT) will exhibit during the projection period under consideration. This study examines 18 case study areas in Texas, along with a detailed look at Dallas County, to determine the factors which significantly affect ADT growth rates for use in the HEEM. The factors include highway capacity, and different categories of land development. The accuracy of ADT projections in Dallas County, along with population and land use projections, are examined, as well as factors which seem to be influencing the size of the errors. Various alternative changes to the HEEM's traffic growth rate formulas are proposed, along with a simple multiple regression model to project ADT. The data are reported in narrative, graphic, and tabular form. Implementation of the findings and recommendations of this report should result in more accurate estimates generated from the HEEM at a lower cost of running the model.