Verification, Refinement, and Applicability of Long-Term Pavement Performance Vehicle Classification Rules

The Long-Term Pavement Performance (LTPP) project has developed and deployed a set of rules for converting axle spacing and weight data into estimates of a vehicle’s classification. These rules are being used at Transportation Pooled Fund Study (TPF) weigh-in-motion (WIM) sites across the country. This report examines the performance of those rules and the implications of their use for the development and application of default values for use within the Mechanistic-Empirical Pavement Design Guide. The report is divided into three parts. In part I, the report examines 1) how the LTPP rules differ from classification rules used by many States, 2) the performance of the LTPP rules in terms of their accuracy across truck types and at different LTPP WIM sites across the country, and 3) the size of the error that can be introduced into the estimation of traffic loading inputs for pavement design when load spectra developed from the LTPP TPF sites using these rules are combined with truck volume data collected using State-specific classification rule sets. Part II of this report examines the sensitivity of the pavement design models to the errors introduced by the use of these traffic loading inputs. Based on the results of these sensitivity tests, recommendations are made about the use of load spectra computed using Specific Pavement Studies TPF WIM data. Part III of this report describes minor changes to the LTPP classification rules recommended to improve their performance. Finally, the results of field tests of the recommended revised classification rules are presented