Safety Evaluation of Improved Curve Delineation

7130231962009Amjadi, RoyaPDFTech ReportFHWA-HRT-09-045HRDS-06/09-09(WEB)EDTFH61-05-D-00024Highway curvesHighway delineatorsRoad markingsTraffic signsHighway safetyEvaluation and assessmentUnited StatesUnited States. Federal Highway AdministrationSrinivasan, RaghavanBaek, JongdaeCarter, Daniel L.Persaud, BhagwantLyon, CraigEccles, Kimberly A.Gross, Frank B.Lefler, NancyVHB/Vanasse Hangen Brustlin, Inc.Persaud Lyon, Inc.University of North Carolina (System). Highway Safety Research CenterUnited States. Federal Highway AdministrationCouncil, Forrest M.Hamlett, CharlesAmjadi, RoyaFederal Highway AdministrationThe Federal Highway Administration (FHWA) organized a pooled fund study of 26 States to evaluate low-cost safety strategies as part of its strategic highway safety effort. One of the strategies chosen to be evaluated for this study was improving curve delineation.Geometric, traffic, and crash data were obtained at 89 treated curves in Connecticut and 139 treated curves in Washington to determine the safety effectiveness of improved curve delineation. Treatments varied by site and included new chevrons, horizontal arrows, and advance warning signs as well as the improvement of existing signs using fluorescent yellow sheeting. All sites were on two-lane rural roads. To account for potential selection bias and regression-to-the-mean, an Empirical Bayes (EB) before-after analysis was conducted. The aggregate results revealed an 18-percent reduction in injury and fatal crashes, a 27.5-percent reduction in crashes during dark conditions, and a 25-percent reduction in lane departure crashes during dark conditions. The reductions were more prominent at locations with higher traffic volumes and sharper curves (curve radius less than 492 ft) and in locations with more hazardous roadsides (roadside hazard rating (RHR) of 5 or higher) compared to locations with less hazardous roadsides (RHR of 4 or lower). In addition, curves where more signs were either added or replaced (with a more retroreflective material) within the curve experienced larger reductions in crashes. An economic analysis revealed that improving curve delineation with signing improvements is a very cost-effective treatment with the benefit-cost ratio exceeding 8:1