Frictional Performance of Pavements and Estimates of Accident Probability

Objectives of this study were to evaluate standard and experimental surfaces throughout Kentucky in terms of skid resistance and effects of traffic, and to provide criteria for judging suitability of these surfaces to satisfy requirements for skid resistance and economics. The effects of traffic were quantified by regression analysis and scatter of data. Criteria included an estimate of accident risks, effects of speed on skid resistance, and seasonal variations in skid resistance. Pavements on low volume roads (less than 1000 vehicles per day) maintained adequate skid resistances. Open-graded friction courses, with the possible exception of sections using phosphate slag aggregate, maintained adequate skid resistance to meet design requirements. The adequacy of other pavements may be judged from the criteria provided herein. Estimates of accident reduction were made by combining the relationship between skid numbers and accidents with the distribution of skid numbers for each pavement type. Those reductions were used to calculate benefits that, along with costs of overlay, were used to determine benefit-cost ratios. Benefits exceeded costs for roads having annual average daily traffic (AADT) greater than 750, 2500, and 5000 and skid numbers (SN) less than 24, 30, and 35, respectively.