Impact of truck characteristics on pavements: truck load equivalency factors

Truck load equivalency factors relate vehicle axle loads to pavement damage and life. They provide a method to convert the effects of mixed traffic to a standard loading condition. Equivalent loadings for most pavement design and evaluation procedures are currently predicted using the AASHTO method of equivalency factors. This study was undertaken to evaluate various types of primary pavement response derived load equivalency factors. These use pavement response measurements such as strain and deflection to estimate the equivalent damaging effect of any axle loading condition. These types of factors are also expressed in terms of a relative number of equivalent standard axle loads. A number of primary response equivalency factor methods were evaluated and several selected for further study. Deflection and strain pavement response measurements were evaluated over an experimental factorial of axle type, axle load, tire pressure, speed, pavement thickness, and pavement temperature. Primary response load equivalencies were calculated using the selected methods and a number of statistical comparisons were made. Results of the study indicate that the concept of primary response truck load equivalency factors is viable and can be extremely useful for estimating load equivalence for pavement design and research purposes. Results also indicate which of the vehicle and pavement factors studied most significantly effect the estimate of load equivalency. Recommendations are also made for use of primary response load equivalencies and for further research into the subject.