Evaluation of the New Virginia Dept. of Highways and Transportation Skid Testing Trailer

About the report:

The purpose of this study was to evaluate the new skid trailer obtained by the Virginia Department of Highways & Transportation and to determine how the survey skid testing program should be conducted in light of the findings. Specifically, those things considered about the new trailer were: (1) testing precision; (2) operational error, defined as unexplained day-to-day variation; (3) the speed-skid number relationships obtained for some customary surface types used in Virginia; and (4) the relationship of the new skid trailer to the Research Council's skid trailer and stopping distance car. Based on the findings of the study several recommendations were made, including the following: (1) Normal survey testing should be done at 40 mph (64 km/h). (2) Corrections to skid numbers obtained at speeds other than the intended test speed should be based on a slope of -.55. (3) Control site testing should be included as a normal part of survey skid testing, and skid test results should be adjusted based on control site test results. (4) Survey skid test data collected with the trailer should be reported in terms of predicted stopping distance car skid numbers based on regression results obtained in this study. (5) The relationships between the three testing devices should be verified at least annually. (6) The testing rate in the survey program should be five tests per lane mile. (7) At sites having borderline skid resistance, additional testing should be run with the trailer before taking action or verifying the results with stopping distance car tests when the standard deviation of the trailer results exceeds 2.25.

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