The Austrian guideline regulating pavement design is currentlybeing revised in the light of increasing heavy vehicle trafficand changes in the technical equipment of heavy freight vehicles.To calculate the expected traffic load for the design period themodification will not longer employ the well-known Fourth PowerLaw. Instead the damaging impact on the pavement structure (withfatigue as the criterion) is determined in a direct approach fromthe fatigue effects due to the passage of different axle loadsand axle configurations.

A comprehensive sensitive analysis examines the key componentsof fatigue caused by single and twin tyres and different axleconfigurations on asphalt pavements by taking into account theirlateral distribution in the cross section of a road lane. Detaileddata for lateral distributions of loads evaluated due to fieldmeasurements and comprehensive information on the distributionof axle loads and heavy vehicle types found in Austria's federalroad network provide the basis for computation of mean equivalencyfactors for different vehicle types and characteristic collectivesof heavy freight vehicles. These are used to determine the relevantdesign load for routine design purposes and will be incorporatedin the modified Austrian design guideline for asphalt pavements.