Impact of Equivalent Loading Frequencies on Flexible Pavement Distress Predictions

The Pavement ME methodology utilizes the concept of equivalent loading frequency to calculate strains within flexible pavement layers through static linear elastic analysis. These calculated strains are then directly used in calculating pavement damage and predicting distresses. Therefore, accurately calculating the loading frequencies is crucial because it can significantly influence pavement performance predictions. In this paper, the effect of loading frequencies on the prediction of long-term pavement distresses is analyzed. Four pavement structures, based on actual freeway designs in Michigan, are selected to examine the effects of loading frequencies on long-term (20-year) pavement distress prediction by comparing rutting and fatigue cracking predicted by the original and corrected Pavement ME frequencies using the Mechanistic-Empirical Pavement Analysis (MEAPA) software. The results show that the difference between bottom-up fatigue cracking predicted by these two frequencies is negligible (<5%), whereas the original Pavement ME frequency underestimates rutting with an error ranging from approximately 15% to 25% for asphalt concrete rutting and from 5% to 10% for total rutting, depending on pavement structures and traffic volumes. The corrected loading frequency method consistently forecasts substantially higher levels of top-down cracking compared with the original Pavement ME, with discrepancies reaching up to 130%. However, it should be noted that the top-down cracking model in MEAPA is based on principal tensile strains near the surface, which is different from the model used in the current Pavement ME model. Nonetheless, there is a potential that the original Pavement ME method may substantially underestimate the extent of top-down fatigue cracking.