FACTORS THAT AFFECT TRAFFIC GROWTH RATES AND PROJECTION OF TRAFFIC VOLUMES FOR USE IN HIGHWAY ECONOMIC MODELS

The magnitude of potential highway user benefits and costs that result from proposed highway improvements must be estimated with a reasonable degree of accuracy for highway agencies to make rational decisions in the public interest. One of the important aspects of most highway economic analysis models is the assumed traffic growth-rate pattern, which is based on one or more projected traffic volumes. The effects of different growth-rate patterns on the estimate of future benefits from a proposed project, as well as the factors that affect traffic projection errors from data collected in Dallas County, Texas, are examined. These factors include the year the projection was made, the percentage of commercial and industrial land development, and changes in highway capacity. A simple model for projecting future traffic volume is also presented, which is based on a multiple regression analysis of historical traffic volume data and adjustments for capacity changes and land development. The model is tested against the traffic projections collected for the Dallas County study sites, with the model producing somewhat more accurate projections in this sample.