This presentation reports on a before-after safety evaluation of a new part-time protected right-turn signal strategy at signalised intersections applying Artificial Intelligence (AI)-based video analytics. For this purpose, the permissive right-turn signals at five signalised intersections were converted to part-time protected right-turn signals, in which protected right-turn signals were mainly implemented during off-peak hours. The opposing through crash risks in the before and after periods of signal change were compared in terms of Post Encroachment Time (PET) conflict counts and estimation of before-after right-turn crash risks by applying an extreme value theory model.
Results suggest that part-time protected right-turn signals reduce two-thirds of opposing-thorough traffic conflict frequencies. Extreme value theory models suggest that opposing-through crash risks along the treated approaches with part-time right-turn signals reduce by 71%. The average queue lengths of the treated approaches during protected phases did not exceed the average queue lengths during the permissible right-turn phases. Therefore, a part-time protected right-turn signal strategy offers a good safety solution without compromising operational efficiency.
