Damage factor relationships for axle and tire configurations are presented. Adjustment factors are provided to account for variations in load distributions within axle groups, distances between axles of a tandem, and variations in tire pressure for both dual and flotation tire configurations.

Properly accounting for accumulated fatigue of a pavement requires an accurate Measure of traffic volume, proportions of vehicle styles (classifications) within the traffic stream, dates of service, estimate of the average damage factor for each classification, and estimate of the tire contact pressure. Weigh-in-motion equipment in its current form provides all of the above ingredients except for the tire contact pressure. A survey of tire pressures may be made and an average calculated to obtain a rough estimate of the effects of loads concentrated on a smaller area than assumed in the past. Such data described above may be used to determine trends in the use of vehicle styles as well as changes in truck volumes and load distributions.

Adjusting for actual conditions of usage may indicate a pavement design thought to last 20 years may last only 14 to 16 years. Such findings affect both new pavement designs and rehabilitation strategies with accompanying effects upon fiscal plans and policies. Adjusted design EALs might require a different pavement template for new designs and a resulting change in costs. Likewise, rehabilitation strategies may change, for example, from a simple overlay to milling and overlay or to complete rehabilitation because of overhead clearance problems, involving additional costs for shoulder paving and replacement or resetting of guard rails, etc. Therefore, estimating EAL requirements may be far more significant and important than previously recognized. Efforts should include the best method to determine the most accurate fatigue history possible.

All adjustment factors presented are based on the analyses of a limited number of structures and should be used with caution. The accuracy of these analyses are not in question, but the range of structures investigated was limited. They are intended to indicate the trend, shape, and sensitivity of various inter-relationships and their relative magnitudes. Modifications may have to be made upon the analyses of additional pavement structures. Kentucky traffic may differ from that in other areas in the United States, both in types of vehicles in the traffic stream and the type and direction cargo is being transported.

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Kentucky Transportation Cabinet, the University of Kentucky, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.