Reducing Roadway Departure Crashes at Horizontal Curve Sections on Two-lane Rural Highways

Federal Highway Administration2019PDFTech ReportDonnell, Eric T.Porter, Richard J.Li, LingyuHamilton, IanHimes, ScottWood, JonathanUnited States. Federal Highway Administration. Office of SafetyThomas D. Larson Pennsylvania Transportation InstituteVHB/Vanasse Hangen Brustlin, Inc.Cheung, JosephUnited States. Federal Highway Administration. Office of SafetyUnited StatesRan off road crashesTraffic safetyHighway curvesRural highwaysTwo lane highwaysTraffic safetyHorizontal curvesRoadway departureDesign consistencyDelineatorsGuiderailCurve warning pavement markingsEmpirical BayesPropensity scoresFHWA-SA-19-005DTFH61-12-C-00032Cheung, JosephWhile several proven safety countermeasures and strategies exist to mitigate roadway departure crashes on horizontal curve sections of two-lane rural highways, there are several countermeasures or strategies that have yet to be proven via a rigorous safety evaluation. The purpose of this research was to identify several of these strategies or countermeasures, and to perform a statistical assessment of their safety effectiveness. This report details the following three evaluations: (1) observational before-after study of curve ahead warning pavement markings, (2) cross-sectional study of delineators on guiderail along horizontal curves, and (3) cross-sectional study of the safety effects of geometric design consistency. The findings from these evaluations indicate that the expected number of roadway departure crashes are associated with the horizontal curve radius, radii of adjacent horizontal curves, and the tangent lengths between curves. Further, the expected number of roadway departure crashes is associated with side friction demand on horizontal curves. Guiderail with delineators are expected to reduce total, fatal plus injury, run-off-road (ROR), and nighttime crashes along horizontal curves that are four degrees or sharper. Horizontal curve warning pavement markings are associated with fewer expected total, fatal plus injury, ROR, nighttime, nighttime ROR, and nighttime fatal plus injury crashes on two-lane rural highways.109