The 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 signing. Treatments varied by site and included new chevrons, horizontal arrows, advance warning signs, and 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 before-after analysis was conducted. The aggregate results revealed an 18 percent reduction in injury and fatal crashes, 27.5 percent reduction in crashes during dark, and 25 percent reduction in lane departure crashes during dark. The reductions were more prominent at locations with higher traffic volumes, sharper curves (curve radius less than 150 meters), and in locations with more hazardous roadsides (roadside hazard rating of 5 or higher) compared to locations with less hazardous roadsides (roadside hazard rating 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 enhancements is a very cost-effective treatment with the benefit cost ratio exceeding 8:1.
Abstract