Investigating the Safety Effects of Median Separation Layout on 2+1 Roads

Evaluations of 2+1 roads focus mainly on the comparison between two-lane rural roads and three-lane configurations, indicating all the safety benefits of the latter. In Poland, several solutions are currently adopted for separating traffic directions, which include only horizontal marking, horizontal marking with additional measures to improve safety (low or high safety devices), and physical separation using cable barriers. However, the literature lacks studies about the impact of all the above-mentioned median separations on safety. When the target of the investigation is the safety performance of 2+1 roads, their contribution cannot be ignored. Based on this assumption, the aim of the present research work is to investigate the safety performance of 2+1 roads, considering various solutions for separating traffic directions, considering the accident’ costs. The methodological approach includes the statistical inference by means of regression models quantifying the predicted number of crashes considering exposure and other variables. The quantification is carried out by calibrating the Safety Performance Functions (SPFs) for total crashes, based on the traffic flows, inventory and crash data. To develop the SPF model the generalized linear regression modeling (GLM) approach was used by calibrating the model on homogeneous segments. Crash Modification Factors (CMFs) for 2+1 roads were estimated to evaluate the influence on the safety of the various solutions of separating. The lowest cost of crashes is expected for cable barrier separation, although the greatest number of crashes but mainly non-injured is observed.