Some Surface Roughness, Loss, and Slipperiness Characteristics of Unpaved Roads

Abstract

An extensive investigation into the performance of materials used in wearing courses for unpaved roads in southern Africa has recently been completed. This involved the routine monitoring of 110 sections of selected gravel roads covering a range of material types, climatic regimes, traffic volumes, and road geometrics. Monitoring involved the routine measurement of road roughness, gravel loss, corrugation and rut development, and a routine description of the surface condition. This paper briefly describes the results of the roughness, gravel loss, and slipperiness investigations. Models for the prediction of roughness and gravel loss are described and compared with models developed in other countries. Significant differences between the models are noted. The investigation into the slipperiness of unpaved roads is described, and the slipperiness when dry is shown to be directly related to the grading and plasticity of the material.