STATE-OF-THE-ART REVIEW ON EQUIVALENT AXLE LOADING FOR FLEXIBLE PAVEMENT DESIGN

In an effort to estimate the damage associated with the heavier vehicles using today's highways, considerable work has been directed toward evaluation of load equivalency factors for different axle loads and axle configurations. Various methods of evaluating equivalency factors were reviewed. The AASHTO load equivalency factors were based on empirical performance data obtained at the AASHO Road Test. For the most part, other methods have been based either on pavement response (maximum surface deflection, maximum tensile strain, etc.) or pavement distress (rutting, fatigue cracking, etc.). The AASHTO equivalency factors were calculated for single and tandem axle configurations only. Accordingly, extrapolation has been required to evaluate newer axle configurations. The results of a survey (telephone, written correspondence, and research report review) indicate that the 18 kip (80 kN) single axle equivalency factors developed at the AASHO Road Test are still in wide use both in the United States and abroad. /FHWA/