Road roughness is gaining increasing importance as an indicator of road condition, both in terms of pavement performance, and as a major determinant of road user costs. This paper defines roughness measurement systems hierachically into four groups, ranging from profilometric methods (2 groups), through response type road roughness measuring systems (RTRRMS's), and, subjective evaluation. The International Roughness Index (IRI) is defined, and the programs for it's calculation are provided. The IRI is based on simulation of the roughness response of a car travelling at 80 km/h. The report explains how all roughness measurements can be related to this scale, also when travelling at lower speeds than 80 km/h. The IRI emerges as a scale that can be used both for calibration and for comparative purposes.

This synthesis will be of interest to construction engineers, pavement designers, contractors, and others interested in construction of new highway pavements with smooth surfaces. Information is provided on the various devices and specifications that are being used to obtain smooth pavements. The public rates a pavement primarily on its smooth-riding characteristics and highway agencies recognize that constructing smooth pavements results in fewer problems later and lower annual maintenance costs. This report of the Transportation Research Board describes the devices and specifications highway agencies use to ensure that newly constructed pavements will provide a smooth ride.