APPLICATION OF THE INTERNATIONAL ROUGHNESS INDEX TO RESPONSE-TYPE MEASURING SYSTEMS. SIXTH INTERNATIONAL CONFERENCE, STRUCTURAL DESIGN OF ASPHALT PAVEMENTS, VOLUME I, PROCEEDINGS, UNIVERSITY OF MICHIGAN, JULY 13-17, 1987, ANN ARBOR, MICHIGAN

Characterizing the roughness of a road in a universal, consistent, and relevant manner has proven to be a persistent problem over the past 40 years. Two major problems are: (1) measuring methods have not been stable with time; and (2) measuring methods have not been transportable. In response to these problems, The World Bank and The Brazilian Ministry of Transportation initiated the International Road Roughness Experiment (IRRE), held in Brasilia, Brazil, in 1982. The experiment and subsequent analyses included the participation of researchers and equipment from Brazil, England, France, Belgium, Australia, and the United States. Representative roughness measuring equipment was operated over test sites in the area around Brasilia that included asphalt pavements and unpaved roads. The data obtained were analyzed with the objectives of determining correlations between the various equipment and limitations on their use. The findings showed that it is possible for all of the equipment to measure roughness on the same scale, if the scale is carefully chosen. Thus, an International Roughness Index (IRI) was proposed for future work to eliminate much of the difficulty experienced in earlier studies. The IRI is based on the concept of the ubiquitous response-tye measuring system--a vehicle equipped with a roadmeter. These systems are used throughout the world in both developing and developed countries. The IRI is defined, however, by a mathematical procedure that is applied to a measured profile, called a quarter-car simulation. The IRI can be measured directly by rod and level methods or by high-speed profilometers. In a validation study, all of the response-type systems that participated in the international experiment could be calibrated to the IRI without loss of accuracy.