Incorporating Wet Pavement Friction into Traffic Safety Analysis

2010PDFTech ReportJHR 10-324Crash dataCrash ratesDrivewaysFrictionHighway curvesPavementsTraffic safetyWet weatherConnecticutIvan, John N.Ravishanker, NaliniJackson, EricGuo, SizhenAronov, BrienUniversity of Connecticut. Connecticut Transportation InstituteConnecticut. Department of TransportationUS Transportation CollectionThis report focuses on analysis of statistical association between wet pavement friction and crash incidence, controlling for pertinent road characteristics such as shoulder width, speed limit, curves, intersections, driveways and area type. The objective of this project was to answer the following questions: (1) Is wet pavement friction significant for explaining variation in crash history among similar locations on the road network? (2) Is this association more relevant at locations with high expected braking frequency, such as sharp curves and intersections? The analysis data were combined from \u201cfound\u201d data locations at which the Connecticut Department of Transportation has previously measured the wet pavement friction, and \u201crandom\u201d data locations at which the friction was measured specifically for this project. Including the random data locations was necessary to avoid bias in the found data due to those locations having been selected due to having experienced one or more crashes or the segments having been placed on the State List of Surveillance Study Sites (SLOSSS). Road characteristics, including shoulder width, speed limit, grade, curvature, presence of driveways and intersections and three years of crash count data (moderate severity to fatal crashes only) were collected and incorporated into the data set. Negative binominal regression was used to estimate models with coefficients for the main factors and interactions. The results show an association between wet pavement friction and crash frequency. The locations where improving the wet pavement friction will most reduce crashes include sections with non-isolated curves on undivided roads and sections with driveways or mild curves on divided roads. The finding of an increase in crash frequency with increases in friction in urban areas, especially on divided roads, suggests reevaluating decisions to improve friction in those locations.90