The Highway Design and Maintenance Standards Model, HDM-III, based on the Brazil-UNDP field study conducted between 1976 and 1981, predicts the average annual road roughness of engineered unpaved roads as a function of five variables - traffic volume, material properties, road geometry, environment and grading frequency. This note presents examples of HDM-III predictions for a lateritic gravel road and for an earth road, and may be used more generally as a guide for the estimation of roughness of unpaved roads when more precise measurements are not available.