Comparing Standard Load Equivalency Calculations for Pavement Management Systems

Pavement Management, at the network level as well as at the project level, requires that load equivalencies be used to define traffic inputs. For the past 30 years, load equivalencies have been calculated using the performance equations developed for the AASHO Road Test. In these performance equations, traffic and accumulated loads are used as indications of performance (that is, serviceability versus accumulated load applications or pavement distress versus accumulated load applications). The paper discusses the load equivalencies recently developed from reanalyses of the AASHO Road Test data. This paper refutes the load equivalencies presented in the book, Road Work, published by the Brookings Institution. This paper also briefly reviews load equivalencies derived from two other studies, one by Illinois Department of Transportation and one by Paul Irick. The paper concludes that the conventionally accepted load power ratio of the fourth power law is still correct and the AASHO Road Test load equivalencies are nearly correct and should remain as a standard for calculating load equivalencies.