Comparative study for safety performance measures of signalized intersection sites

Abstract

The decision on which safety performance measure to use for diagnosis of sites with probable to profit from safety improvements is a major factor in making the right decision for the guidance of resources. This study concentrated on introducing a quantitative comparison of sites according to four crash-based methods suggested in the Highway Safety Manual (HSM). Archived crash data for three years are obtained to conduct a comparison course. As a case study, the analysis and measure of safety for 9 four-leg signalized intersections in Baghdad city have been done independently using Empirical Bayes method (EB-method), observed Crash Frequency (CF), Crash Rate (CR) and Empirical Bayes Adjustment (EB-adj.) as safety performance measures in HSM. In this paper the EB-method is used as a benchmark for comparison. The safety measures are evaluated through rank correlation analysis while hazard location identification results are compared through the use of values rank-based mean absolute error. Quantitative evaluation tests showed that each of EB-adj and observed CF correlated well with EB-method while CR method exhibited poor performance in comparison with EB-method and was the worst in hazard location identification. This result is quite confusing since many agencies still depend on the CR method in traffic safety analyses.