Comparison of Profile Index and International Roughness Index for Pavement Smoothness Incentive Specifications
The Minnesota Department of Transportation (Mn/DOT) is currently evaluating a change from the Profile Index (PI) to the International Roughness Index (IRI) for smoothness specifications for portland cement concrete (PCC) pavements. This change has already occurred for bituminous pavements in Minnesota. The Mn/DOT Office of Materials, as well as paving contractors in Minnesota, is naturally concerned with the effects that this change will have on the quality of pavement surfaces and on the incentives paid for new pavement smoothness. The Office of Materials has funded an “implementation” project to compare the two smoothness statistics and to provide recommendations for implementing the new specification. This paper contains several analyses and comparisons of the relative effects of pavement features in design and construction with regard to the results of pavement surface smoothness and incentive computations. It also contains an analysis of segment length for incentive/disincentive calculations on PCC pavement projects. The information presented in this paper can be useful to those considering changing pavement smoothness specifications from profile index to international roughness index. This paper was submitted to the Transportation Research Board for the 2007 Annual Meeting.