Gravel Roads Surface Performance Modeling

Abstract

Twenty gravel road study sections at 10 sites in north-central Wyoming were monitored from September 2005 through June 2006. Windshield or mobile, visual survey ratings of the sections and field measurements were taken weekly. Surfacing gravel samples were collected, and their gradations were determined. Traffic speeds and volumes by class were collected with a two-tube system. (A two-tube system counts traffic by receiving signals from two tubes placed 8 ft apart across the road. By a comparison of the times at which signals are received from each tube, the speed of the traffic can be determined, as can the number and spacing of axles.) Statistical analyses generated regression models that allowed the prediction of the service life of an unmaintained gravel road. Traffic speeds, traffic volumes, and surfacing gravel properties were shown to have the greatest influence on gravel roads’ deterioration rates. For these typical Wyoming county roads with good geometry, good drainage, and adequate gravel thicknesses, the typical failure mode was shown to be either potholes or washboards (corrugations). The typical life of gravel roads without maintenance was shown to be in the range of several months to 1 year. Climatic effects were shown to be related to precipitation more than seasonality, at least in Wyoming's dry–freeze climate.