Wet pavements crash study of longitudinal and transverse tined PCC pavements

Abstract

This report provides crash statistics for Longitudinally Tined (LT) Portland Cement Concrete (PCC) and Transversely Tined (TT) PCC pavement surfaces. The statistics were compiled for urban and rural freeways, classified in two Average Daily Traffic (ADT) categories: pavements carrying less than 60,000 vehicles per day (VPD) and those carrying an ADT in excess of 60,000 VPD. Crash experience on California LT PCC pavements was compared to that of Wisconsin TT PCC pavements. Safety performance of wet pavements was the focus of the analysis. Rural freeways were considered to be ideal for this study, given the prevailing high speeds, absence of extraneous influences on safety (e.g., cross streets, onstreet parking, pedestrians, traffic signals), and consistent design standards between the comparison states. Rainfall differences were accounted for with the use of hourly precipitation data, and terrain differences were taken into account by using level and rolling terrain California freeways (excluding mountainous terrain ones). Statistics were based on eight years of crash and hourly weather data (1991-1998). Crash rates were computed based on hundred-million-vehicle-miles of travel (HMVM)--more than 72 HMVM for Wisconsin and more than 500 HMVM for California. No statistically significant differences in safety performance were found between rural LT freeways (California) and rural TT freeways (Wisconsin) with ADT less than 60,000 VPD. It is recommended that safety comparisons between the two pavement textures be expanded to include winter pavement surface conditions when snow or ice are present on the roadway surface. If no significant safety performance differences are found under such conditions, LT PCC pavements may be preferred over TT ones, since they generate lower levels of tire-pavement noise.