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New Zealand's road network utilizes pavement types of widely differing properties, ranging from very smooth asphaltic concrete to coarse chipseal surfaces having macro-texture levels not often found elsewhere in the world. An experimental program, therefore, was undertaken to investigate the effect of surface texture on the rolling resistance of a typical tire/car combination. A comparison of the coastdown and steady-state torque methods established that the latter was more suitable for measuring vehicle drag forces on public roads. Accordingly, it was used to obtain static and dynamic rolling resistance coefficients for twelve different road surfaces having approximately the same roughness, but with macrotexture depths which varied from 0.14 to 2 mm. The coarsest-textured surface investigated had a static component of rolling resistance that was 55% greater than that of the smoothest. Regression analyses established that the static component of rolling resistance is strongly correlated to surface profile wavelengths between 2 and 50 mm. In addition, a limited investigation of rolling resistance changes due to aging/traffic loading effects was conducted for a porous friction course surface.
rolling resistance, road surface texture, vehicle operating costs, road/tire interaction, chipseal, coastdown, steady-state torque method
Section Head, Works Consultancy Services Ltd., Central Laboratories, Lower Hutt,