Interconversion of Locked-Wheel and Continuous Friction Measurement Equipment (CFME) Friction Measurements

As transportation agencies are adopting proactive pavement friction management using continuous friction measurement equipment (CFME), the need for a method that allows interconversion between the traditional locked-wheel skid testers (LWSTs) becomes important to assure continuity with past practices. This paper evaluates several conversion methods based on the International Friction Index (IFI) approach and proposes an alternative method that allows predicting the measurements of the LWST using measurements with the Sideway-Force Coefficient Routine Investigatory Machine (SCRIM). The investigation is based on data collected using a SCRIM and two LWSTs on a controlled pavement test facility. The results suggest that a conversion based only on the speed adjustments (FR60) is the most effective method to predict the LWST measurements from SCRIM measurements. The coefficient of determination and average absolute error are comparable to those using the full IFI F60 formula but do not require static reference measurements. The study also showed that the three tested devices produced appropriate repeatability as computed using the limit of agreement at the three tested speeds and on a wide range of surfaces.