Comparison and Harmonization of the Locked-Wheel Skid Tester and the Sideway-Force Coefficient Routine Investigation Machine

Abstract

Abstract Skid resistance is a characteristic of a pavement surface that is critical to pavement safety. Skid resistance can be measured with different types of equipment, but because of the differences in the system configurations and the testing methods (fixed slip, locked-wheel, sideway-force, and variable-slip), the measured friction characteristics are not the same. To compare the measurements, analysts have attempted to harmonize measurements to a common scale by integrating the effects of macrotexture and slip-speed on skid resistance. Examples of these efforts include the Penn State model, the Rado Model, the Permanent International Association of Road Congresses International Friction Index (IFI), and the Rolling Resistance, Skid Resistance, and Noise Emission (ROSANNE) Skid Resistance Index (SRI). In the United States, skid resistance is traditionally measured with a locked-wheel skid trailer (LWST), but there has been increasing interest in the use of continuous friction measurement equipment. This paper compares friction measured using a LWST ribbed tire and smooth tire with measurements collected with a Sideway-Force Routine Investigation Machine (SCRIM). The first objective is to evaluate the influence of macrotexture on the friction measured with both devices. The second objective is to compare the friction measurements using orthogonal regression (OR) and derive equations for interconversion between both devices. The findings in this paper establish that the LWST ribbed tire and the SCRIM shared similar sensitivity to changes in microtexture, whereas smooth tire was more sensitive to changes in microtexture. The direction of the OR of both devices produced a greater correlation for the SCRIM and ribbed tire than did the smooth tire. The correlation was increased when the measurements with the SCRIM and smooth tire were converted to 60 km/h using the IFI FR60 conversion. The higher correlation using FR60 conversion provides further support for the dependence of smooth tire friction on macrotexture measurements.