This report summarizes a brief analysis of Washington State Department of Transportation (WSDOT)'s weigh-in-motion data. The report includes data from ten permanent WIM sites: four bending plate scales and six piezo-electric scales. The intent of this report is to provide an overview of the truck loading patterns observed at these sites, and to provide improved ESAL loading estimates for use by WSDOT. The ten sites selected for this study reflect the variety of traffic loading conditions found within the state. They are geographically dispersed across the state, represent a number of functional roadway classes, and serve a range of traffic volumes.
The WSDOT collected the data according to the 13 vehicle classifications set by the FHWA; the results in this report are presented with reference to both the FHWA system and to the WSDOT system. The WSDOT system, which is used in its pavement design guide and is incorporated into its traffic data computer system (TRIPS), divides vehicles into four classes: cars, single units, double units, and multitrailer units.