Researchers
About the research
Pavement friction significantly contributes to roadway safety by providing the grip required for safe travel. The Iowa Department of Transportation (DOT) has long recognized the importance of evaluating pavement skid resistance and its impact on traffic safety.
Several devices have been developed to measure skid resistance. The Iowa DOT currently uses the locked-wheel skid tester (LWST), which is well accepted across the United States and globally. Due to its relatively narrow speed range and limitations on curves and short, low-speed segments, various types of continuous friction measurement equipment (CFME) have been proposed as alternatives, including the GripTester and sideway-force coefficient routine investigation machine (SCRIM). A broader issue in friction measurement is repeatability and reliability under different operational conditions, with temperature, pavement wetting, and test speed affecting the correlation between different devices.
This study aimed to evaluate candidate CFME technologies for their ability to measure pavement friction at different test speeds and in different operational conditions relative to the LWST currently available at the Iowa DOT. Promising CFME technologies were selected, and a testing program based on statistical procedures was designed to evaluate the devices’ suitability for pavement friction evaluation in relation to the friction demand and safety analysis. CFME and LWST testing was performed at three asphalt and three concrete pavement test segments at different speeds and using smooth and ribbed tires, and tests were repeated on different days to determine performance in different operational conditions. A dynamic friction tester (DFT) and laser texture scanner (LTS) were used to verify the correlation between the CFME and LWST and to investigate the impact of pavement texture on dry and wet skid resistance.
The research resulted in guidance and recommendations for friction evaluation on different components of the network, including curves and low-speed segments. These outcomes represent a step toward a consistent procedure for both routine pavement friction evaluation at the network level and spot investigation for high-risk areas.