TRR No. 1260 Pavement Design, Management And Performance, pp.106-111
Road roughness is normally characterized by a summary index that applies over a length of road. Summary index measures are obtained most directly by measuring the longitudinal profile and then applying a mathematical analysis to reduce the profile to the roughness statistic. The moving average smoothing filter can be used to obtain a profile of one such roughness measure-the international roughness index (IRI). The roughness profile provides another dimension to the description of roughness, showing with maximum detail how the roughness is distributed over the length of the road. The baselength used for the IRI averaging must be considered. Specifying the baselength becomes particularly important when specifications for road quality are formulated, or when profiling accuracy is prescribe. That the variation in IRI found over the length of a road is more extreme when the baselength is short should be taken into account when reporting instrument accuracy or writing roughness specifications. Specially, the accuracy of high-speed profiling systems should be specified according to baselength.