This report describes the techniques used to evaluate the effects of various axle configurations with dual and single tires on pavement performance and the current State of Washington Regulation RCW 46.44.042. Equivalent wheel load factors were developed for various widths of single tires on both rigid and flexible pavements. Single tires with widths 10 to 18 inches were analyzed and it was found that by equivalent axle loads the predicted damage to pavements was greater for axles with single tires that those with dual tires.
To verify the theoretical analyses, two field experiments were conducted. First, extensometers were placed in the outer wheel path of the pavement ramp at the Fife I-5 weigh station. Truck induced pavement surface deflections were measured after the vehicles were weighed on the scale. A comparison of measured and calculated deflections revealed good agreement thus in part verifying the theoretically based calculations. Second, a field site near Edmondton, Alberta was also used in the verification process by use of the WSDOT Falling Weight Deflectometer. Again the theoretical approach was further verified.