International Roughness Index : Relationship to Other Measure of Roughness and Riding Quality

Different measures of road roughness with varying degrees of reproducibility and repeatability have been applied by various agencies in the world, but the exchange of roughness information has been hampered by a lack of an acceptable reference and a quantitative basis for relating the different measures. Presented in this paper is such a basis developed from an analysis of data from the International Road Roughness Experiment (IRRE) and other sources, The International Roughness Index (IRI), developed from the IRRE as a suitable calibration standard for all response-type and profilometr ic instruments, is the transferable reference scale. It is the metric equivalent of a reference inches/mile index. Two-way conversion relationships and confidence intervals are presented for the Quarter-car Index (QI), British Bump Integrator trailer index (BI), and various profile numerics of the French Analyseur de Profil en Long (APL) (longitudial profile analyzer) profilometer from the IRRE, and for the Serviceability Index from other sources. The characteristics of each scale, and the sources of variation and range of application of the conversions are discussed.