This report provides an up-to date review of the literature on the relationship between skid resistance and crashes. Before and after studies have shown considerable reduction in wet-weather crashes following resurfacing which raises skid resistance. The evidence regarding the effect of improved skid resistance on dry weather crashes is mixed. A re-analysis of one Australian study produced benefit-cost ratios for surface treatments that were estimated at between 15 and 84:1, depending on the type of treatment, which was between four and seven times the benefit-cost ratios estimated in the original study. Regression studies are unanimous in showing that the proportion and/or rate of wet weather accidents increases as skid resistance diminishes, but studies disagree on the nature of the relationship and its strength as expressed by the r-squared measure. Options for intervention programs were discussed. Programs based on regular monitoring of skid resistance that require that an engineering judgement be made when skid resistance level falls below a critical level introduce a degree of flexibility, but may result in inconsistent decisions in the absence of guidelines as to what factors should be taken into account. Programs based on identifying sites with large numbers of wet-weather crashes would seem to hold out the prospect of being highly effective, while requiring no additional data collection. Taking into account factors such as crash type, traffic flow, traffic speed and gradient may result in more closely targeted programs delivering higher crash reductions. (A)
Abstract