This study describes the analysis of truck volume data collected by the Washington State Department of Transportation (WSDOT) over four and one half years, from 1988 through 1993. The primary objectives of this research were to: investigate the patterns in truck volumes at various locations in Washington State; determine whether seasonal factors can be developed and applied to short duration truck volume measurements to better estimate average annual conditions; develop procedures for routinely calculating and applying these values in Washington; develop an easy procedure that other states can use to create their own seasonal factoring process, and produce a guidebook that explains this process and lists the necessary steps clearly and concisely.
This report summarizes all but the last of these objectives; this last objective is met in another summary report.
The project analyses show that it is very difficult to develop and apply truck seasonal adjustment factors that accurately predict annual truck volumes from a single short duration truck volume count. As a result, the project team recommends that, wherever possible and financially appropriate, each state should collect multiple, site specific vehicle classification counts in order to accurately estimate annual truck volumes whenever pavement design projects are to be performed.