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South Dakota Department of Transportation
Project Synopsis

Title: Correlation of Roughness Ratings with Highway User Opinion
Project Researcher: Nuss, Isaac Hall, Mathew,
Project Manager: Mark Mayer
Research Period: 5/22/2002 - 11/30/2002
Cost: $15,000.00

Problem Statement:

The South Dakota Department of Transportation's pavement management system uses a Roughness Distress Index to partially define the overall condition of pavements and as a criterion for selecting appropriate rehabilitation treatments. The index, which is on a 0 (infinitely rough) to 5 (perfectly smooth) scale, was initially based upon the South Dakota Roughness Index (SADI) calculated from high-speed profile measurements when the pavement management system was developed in 1994. The relationship between SDI and the Roughness Distress Index was established from the opinions of a panel of experts at that time.

In 2000, the Department switched to the International Roughness Index (IRI) as the base for the Roughness Distress Index. Because the South Dakota Roughness Index and the International Roughness Index emphasize the contributions of short and long wavelength roughness differently, the relationship between IRI and the Roughness Distress Index could only be approximated.

Because the original panel of experts comprised of SDDOT personnel exclusively, their opinions may not have represented South Dakota's general public opinion. If the panel was more tolerant of pavement roughness than the general public, the importance of roughness might be underrated in the pavement management system. Conversely, if the panel was less tolerant of roughness, the importance of roughness might be overrated.

The uncertainty in how well the Department's Roughness Distress Index matches public perception and in the relationship of public perception to measured IRI causes uncertainty on the validity of pavement management decisions based on the measurements .


Research Objectives:
1  To establish a mathematical correlation between pavement roughness measured as International Roughness Index and highway users' subjective opinion of roughness.
2  To identify thresholds of pavement roughness, in terms of International Roughness Index and subjective opinion, acceptable to highway users.

Research Tasks:
1  Meet with the project's technical panel to review the project scope and work plan.
2  Review literature on methodology and results from previous correlation's of measured roughness to subjective opinion
3  Identify and establish test sections that encompass a wide range of roughness conditions on the pavement families prevalent in South Dakota.
4  Obtain measured roughness ratings (International Roughness Index) and subjective rating from a panel of lay highway users on each of the established test sections.
5  Analyze measured roughness ratings and subjective ratings to determine correlation relationships and thresholds of acceptable roughness levels for each pavement family.
6  Prepare a final report and executive summary of the research methodology, findings, conclusions, and recommendations.
7  Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Documents Available:

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