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In this paper, methods currently in use to measure tire-pavement friction are reviewed. The emphasis is on full-scale measurement systems operated at highway speeds, including systems that measure brake force coefficients (under slip or lockedwheel conditions or both) and side-force coefficients. A comparison is made of the data and information produced by each of these measurement methods. Attempts to relate the data produced by each of these methods are reviewed, and the reasons for their lack of agreement are discussed. In addition to direct traction measurement methods, texture measurements are discussed, and the reliability of texture-friction relationships is reviewed. The influence of texture on each of the full-scale measurement methods is investigated as a means of explaining the lack of agreement of the data produced by these methods.
Tire-pavement traction measurements are used for evaluating pavement safety and for predicting vehicle performance. The procedures for characterizing tire-pavement friction for these two applications usually differ. In the United States, pavements are monitored in annual inventories by a single measurement of skid resistance at a single speed with a standard ribbed test tire. Additional tests at multiple speeds or tests with a blank test tire or both may be conducted at accident sites. In some European countries, side-force coefficients or slip tests, both of which have the advantage of providing continuous measurements, are used to monitor pavement networks. These measurements are generally used in conjunction with a minimum texture depth requirement. A comparison of these approaches with U.S. practice is discussed. In conclusion, the status of consensus standards within ASTM and the International Standards Organization (ISO) is summarized, and recommendations are made for future standards development.
tires, pavements, traction, standards
Professor of mechanical engineering and director of the Pennsylvania Transportation Institute, Pennsylvania State University, University Park, PA