Safety Effects of Median Treatments Using Longitudinal Channelizers: Empirical Bayesian Before-and-After Study

Abstract

A new median treatment technique using longitudinal channelizers has been used in Florida as an alternative to the traditional permanent concrete barrier. However, the effects of the new technique on roadway safety and its economic performance have not been well documented. This paper’s intent is to present the results of a comprehensive evaluation on the safety and economic performance of the longitudinal channelizers’ median treatments with before-and-after crash data. Two types of longitudinal channelizers’ treatments—full median opening to directional median opening and full median opening to left-in only median opening—were evaluated. To account for the site selection bias, the empirical Bayesian before-and-after study method was used. The safety performance function for roadway segments with full median openings was developed with the generalized linear model to consider the negative binomial distribution of the crash counts in population entities. The targeted crash types for the longitudinal channelizers’ median treatment (the left-turn crashes) were reduced by approximately 60 and 45% in the after period for directional and left-in only median treatments, respectively. The economic performance of the longitudinal channelizers’ median treatments was quantified based on the crash analysis results from the empirical Bayesian before-and-after study. The annual cost reductions on crashes per site location were $562,321 and $94,480 for directional and left-in only median treatments, respectively. Benefit-cost ratios of 18.9–224.9 can be achieved with the implementation of longitudinal channelizers’ median treatments. Further application of longitudinal channelizers for median treatment is recommended, especially for those locations where immediate treatments for safety purpose are required.