The need for improved traffic estimation procedures has been emphasized by several studies that demonstrated that previously available data were not adequate. Some data were not considered representative of actual traffic conditions because of overloaded trucks avoiding weighing scales and insufficient traffic sampling programs. In addition, previous forecasting procedures did not reflect the increases in legal load limits, the significant increase in the number of heavy trucks, or the shift toward larger vehicle types that has occurred in recent years.

Improved estimates of current traffic loadings based on larger samples of much higher quality data would allow development of procedures for making improved estimates of historical traffic loadings and better forecasts of traffic loadings during the design period. The emergence of automatic vehicle classification equipment, permanent and portable weigh-in-motion (WIM) systems, and the application of microprocessors and microcomputers to these data acquisition functions now offer tools that may be used effectively in meeting these needs.

Representatives from four States (Florida, Kentucky, Oregon, and Washington) met on several occasions to discuss the subject of traffic forecasting for pavement design. Information was compiled on all aspects of the traffic forecasting process, options were presented for each step of the process, and recommendations were developed to assist highway agencies in improving current practices and procedures.

Report Date


Report Number


Digital Object Identifier



This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange . The United States Government assumes no liability for its contents or use thereof.

The contents of this report reflect the views of the contributors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the policy of the Department of Transportation.

This report does not constitute a standard, specification, or regulation. The United States Government does not endorse products or manufacturers. Trade or manufacturers' names appear herein only because they are considered essential to the objective of this document.