Relationship between International Roughness Index and Straightedge Index

Abstract

This study presents the regression relationships between two commonly used indicators of longitudinal road unevenness, the international roughness index (IRI) and the straightedge index. A total of 290 real longitudinal road-profile records were processed. The asphalt-concrete and cement-concrete road surfaces were analyzed separately. Five differently defined straightedge indexes, i.e., the deviations between straightedge and profiles, were considered. The one-parameter linear approximation without an absolute term seems to be an appropriate model for fitting the unevenness indexes relation. The conversion relationships between five differently defined straightedge indexes were derived. The results were calculated as a function of a straightedge length in the range of 3 to 7.8 m. The two-parameter power function was shown to be the most suitable approximation model of the straightedge indexes dependence on the straightedge length. The analyzed influence of the different slab lengths of cement-concrete profiles on the conversion relationships indicated the marginal impact for the typical slab lengths.