Safety Evaluation of Curve Delineation Improvements

Abstract

The objective of this study was to evaluate the safety effectiveness of treatments aimed at improving horizontal curve delineation. Different target crash types were considered in the analysis: total, nighttime, daytime, rainy, nonrainy, run-off-road, non-run-off-road, injury, and property damage only. The treatment sites for this study were 15 curves of the motorway A16 Naples–Canosa in Italy. All curves were characterized by small radius, large deflection angle, available sight distance smaller than the stopping sight distance, and superelevation smaller than the demanded one at both the design and the operating speed. Treatment typologies included installation of chevron signs; installation of curve warning signs and chevron signs; and installation of curve warning signs, chevron signs, and sequential flashing beacons along the curve. An empirical Bayes observational before-and-after study was performed. Results indicate statistically significant crash reductions in total, nighttime, daytime, rainy, nonrainy, run-off-road, and property-damage-only crashes. Total crash reduction is estimated to be 39.4%. Treatment effectiveness is greater for curves with radius less than or equal to 300 m and for curves with deflection angle greater than 60 gon (100 gon = 90°). Total crash reduction is estimated to be 52.2% for curves with radius less than or equal to 300 m and 51.0% for curves with deflection angle greater than 60 gon. The most effective treatment was the installation of curve warning signs, chevron signs, and sequential flashing beacons along the curve. The statistically significant estimate of total crash reduction for this treatment is 47.6%.