The existing method of measuring deformation in the wheel paths of roads in the UK is by straightedge; it is slow and is hazardous on busy roads. A safer and faster method of measurement using the new TRRL high-speed profilometer has been developed at the Laboratory. This Report describes the method of measurement and the evaluation of the factors affecting the accuracy of measurement. Comparison of the high-speed and existing method of measurement show agreement to within 2mm on major roads and within 3mm on other roads. The difference between the measurements is caused in part by the sampling error of the straightedge method and in part by the operator in controlling the line of measurement of the high-speed system. Repeatability of measurement is found to be such that on average 80 per cent or more of the repeat measurements differ by 1.5 mm or less. Criteria for rut depth derived from existing maintenance criteria are presented for use with the high-speed system. Alternative and less costly equipment than the profilometer that would measure rut depth and surface texture is briefly described.(A)

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