Relating Axle Load Spectra to Truck Gross Vehicle Weights and Volumes

Abstract

Axle load spectra have been used to develop the mechanistic-empirical pavement design guide (M-E PDG). Use of these load spectra provides a more direct and rational approach for the analysis and design of pavement structures to estimate the effects of actual traffic on pavement response and distress. However, the demand for specific truck- and axle load-related data makes the collection of axle load spectra a very complicated, costly, and labor-intensive operation. Due to limited resources available in state and local highway agencies for traffic data collection, the M-E PDG allows for various levels of traffic data collection and analysis. These levels vary from site-specific (Level 1) to regional average (Level 3) traffic load and volume data. This paper explores the possibility of extracting axle loads from truck weight and volume data and presents a practical method of modeling axle load spectra. Axle load-related data used in the analyses cover diversified geographical locations in the United States. The results show that truck weights and proportions on a highway can be used to estimate individual axle load spectra for various axle configurations. The practical implication of these results is that truck weights, which can be measured easily or estimated from existing data, can be related to the axle loads if accurate and rational models are developed for a region based on the local truck traffic characteristics and weights. Such estimates will be superior to assuming a Level 3 input for axle load spectra in the new M-E PDG.