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 .