Relation between power spectral density of road roughness and international roughness index and its application

Abstract

To address issues on the relation between the power spectral density (PSD) of road roughness and international roughness index (IRI), a simple method based on stochastic mathematics is used to derive the relation between the IRI and relative vertical velocity of sprung and unsprung masses of a quarter-car vibration system. The relation between the PSD of road roughness and IRI is also derived. Furthermore, two new concepts comprising time and spatial frequency IRI suitable for any form of longitudinal road-profile PSD are proposed. Based on the up-to-date ISO road classification and the proposed concepts, car-based and truck-based road classifications are presented. Compared with IRI, a new index named IRItr is found to be a better index for ranking road roughness from the perspective of the dynamic wheel load of a truck.