A comparison of collision-based and conflict-based safety evaluations: the case of right-turn smart channels

This study presents the results of a collision-based full Bayes (FB) before-after (BA) safety evaluation of a newly proposed design for channelized right-turn lanes. The design which is termed "Smart Channels" decreases the angle of the channelized right-turn to approximately 70°. Its implementation is usually advocated to afford drivers a better view of the traffic stream they are to merge with and to allow also for safer pedestrian crossing. The evaluation used data for three treatment intersections and several comparison sites in the city of Penticton, British Columbia. The evaluation utilized FB univariate and multivariate linear intervention models with multiple regression links representing time, treatment, and interaction effects as well as the traffic volumes effects. As well, the models were extended to incorporate random parameters to account for the correlation between sites within comparison-treatment pairs. The results showed that the implementation of the right-turn treatment has resulted in a considerable reduction in the severity and frequency of collisions. Another objective of the paper was to compare the results of the collision-based evaluation with the results of a traffic conflict-based evaluation of the same treatment intersections. The comparison showed remarkable similarity between the overall and the location specific reductions in conflicts and collisions which provides support for using traffic conflicts in BA studies. The results also provide positive empirical evidence that can support the validity of traffic conflict techniques.