Procedure for Ranking Unsignalized Rural Intersections for Safety Improvement

The paper presents a ranking procedure for rural unsignalized intersections which uses quantitative safety evaluations performed as part of the safety inspection process. It might be effective for the selection of cost effective treatments at intersections and might be very helpful for administrations which do not have quality crash data and for administrations which manage low volume roads where crash data cannot give enough information on crashes to be prevented. The procedure evaluates a safety index (SI) that can be used to rank intersections for further investigations. SI can be assessed whether crash data are available or not. If crash data are available and their quality is good, SI can be effectively used in conjunction with the EB estimate of frequency as ranking criteria. If crash data are not available or poor, SI can be used as a proxy of crash data and becomes the only ranking criteria. Validation of the safety index procedure was carried out by comparing the results with the EB safety estimates. The SI was assessed in twenty-two three leg intersections in Italy. In the same intersections, a safety performance function was calibrated and the EB refinement technique was used to obtain a better estimate of the existing safety performance. Correlation between SI values and EB safety estimates is highly significant, with 84% of the variation in the estimated number of crashes explained by the SI value. The results from the Spearman's rank-correlation show that ranking from the SI and the EB estimate do agree at the 99.9% significance level.