Evaluation of International Friction Index Coefficients for Various Devices

This paper presents a research effort to compare and harmonize measurements of texture and skid resistance taken with various devices at the Virginia Smart Road in May 2008 by the members of the Virginia Consortium for Pavement Surface Properties. There have been numerous efforts by different countries and agencies to understand better the relationship and behavior of different friction-testing devices and the influence of texture, speed, and other external conditions on these measurements. Measurements obtained with different types of equipment on 24 pavement sections with a wide range of textures were compared, and the relationship between friction and speed for the different pavement sections and devices was studied. Data were collected with two locked-wheel skid trailers, a Griptester, and a dynamic friction tester. Nine asphalt sections were tested; six were Superpave® mixes, two were stone matrix asphalt, and one was an open-graded friction course. The concrete sections tested included one continuously reinforced concrete pavement with tined finishing and two epoxy overlays. Even though all steps included in the specifications derived from the experiments by the Permanent International Association of Road Congresses (PIARC) were followed, the results obtained were not satisfactory. From a theoretical standpoint, all the values computed with the international friction index (IFI) F60 should be equal, but this was not the case. Discrepancies in the IFI values calculated for the different devices suggest that the original coefficients determined during the PIARC experiment may need to be adjusted for the devices evaluated, before the IFI can be implemented by the participating agencies.