United States Department of Transportation
i
Evaluation of Skid Resistance of Idaho Pavements at Different Speeds
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2019-08-01
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[PDF-5.80 MB]
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Edition:Final Report
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Abstract:Adequate skid resistance is essential component of road safety. Various transportation agencies measure the skid number using a locked-wheel skid trailer at a reference speed (e.g., 40 mph). In many cases the skid number is measured at lower speeds due to state speed limits, geometry of roads and size of skid truck. It is well established that the skid number decreases with speed. In addition, several interstates in Idaho have a speed limit up to 80 mph while the skid number is still measured at 40 mph; potentially unsafe for the operators and motoring public. This study aimed to develop a method that can be used to convert the skid number collected at any speed between 20 mph and 60 mph to the corresponding skid number at a reference speed. The researchers measured the frictional characteristics of various pavement sections including hot mix asphalt, seal coat, and concrete. The skid number was measured at five different speeds (e.g., 20, 30, 40, 50, and 60 mph) using a locked wheel skid trailer with smooth tire. The macrotexture of test sections was measured using a laser profiler and sand patch test while a dynamic friction tester was used to measure the microtexture. The researchers developed a statistical-based model to describe the change in skid number with speed. The model utilizes the mean profile depth data and skid number measurements at a given speed and calculates the skid number at a reference speed specified by the user. The predicted skid number values correlated well with the measured ones. The model was further validated with skid data from additional eight test sites that were not used in the model development. In addition, the researchers developed an Excel-based utility software to facilitate the process of analyzing the friction and texture data collected using the ITD pavement friction tester and calculating the skid number at a reference speed.
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