Relationships between various classes of road surface roughness and ratings of riding quality

This paper discusses the development and application of a set of riding quality indexes that characterize the road roughness with different ranges of wavelengths. The indexes are based on the relationship between road surface profile data and rating made by a panel of riding quality and were derived through regression analysis. In the study the roughness was catagorized on the basis of wavelength through digital filtering; four bands spanning the range of 1.219 to 30.48m in wavelength were included. For each band characterizing measures of both the most severe roughness and the average roughness of each road section were computed. The waves in both wheel paths were analyzed along with the surface profile undulations of one wheel-path to the other; the latter causes a vehicle rolling effect. A set of SI (serviceability index) modes was developed that can be used to transform the roughness measures corresponding to each wavelength band into a measure of riding quality that is directly related to the PSR. This was achieved by regressing PSR on the roughness terms for each individual band. Separate models were developed for asphalt concrete and portland cement concrete pavements. In addition to the roughness measures, the models also contain a dummy variable to account for any possible visual or auditory differences between types of pavements that may not be explained in terms of roughness. Stepwise regression was used to develop the regression models and SI models were applied to test cases just before and just after hot mix overlay was performed.