UC Irvine Institute of Transportation Studies

This paper describes a statistical framework that can be used for analysis of statewide traffic count data. It also provides a basis for designing a streamlined and cost-effective statewide traffic data collection program. The procedures described were developed as part of an in-depth evaluation study for the Washington State Department of Transportation. They were used to develop recommendations for an improved, statistically-based, statewide highway data collection program. The program is intended to be implemented readily, and is consistent with the FHWA Highway Performance Monitoring System and the recent FHWA draft Traffic Monitoring Guide. In the latter case, several modifications (improvements) to the statistical framework for volume counting and vehicle classification were investigated, particularly for deriving estimates of annual average daily traffic (AADT) from short duration axle counts at any location on the state highway system. AADT estimates can be derived for each vehicle type, if desired. The estimation of associated seasonal, axle correction and growth factors is also described. The methodology enables the statistical precision of all estimates to be determined. The results obtained from applying these procedures to Washington State traffic data are presented.