Relationships were developed between wet-pavement accident rate and skid number for various combinations of highway type, area type (urban/rural) and traffic volume. Accident rate, skid number and related data were collected for two one-year periods on 428 highway sections located in 16 states. An extensive statistical analysis of the data was conducted using matched-pair comparisons, regression analysis and analysis of covariance. The analysis found a small, but statistically significant, influence of skid number on wet-pavement accident rate. A linear relationship with skid number explained the variation in wet-pavement accident rate as well, or better, than any simple logarithmic or polynomial function. The differences in the slope of this linear relationship for various highway type-area type-traffic volume combinations were not statistically significant, so a single common slope was used. It was found that the slope of the wet-pavement accident rate-skid number relationship is sensitive to the dry-pavement accident rate. This sensitivity was quantified to further explain the relationship between wet-pavement accident rate and skid number. The relationships developed in this volume have been incorporated in a computerized benefit-cost model for wet-pavement accident countermeasures, described in volumes ii and iii of this report.(a) for vols ii and iv of the report see IRRD nos 251663 and 251664.
Abstract