Left-turn phasing selection considering vehicle to vehicle and vehicle to pedestrian conflicts

Abstract

Left-turning vehicle movement at signalized intersections with permissive left-turn phases creates safety concerns due to the higher chance of conflict with opposing-through vehicles and pedestrians. In this research, a simulation-based study was conducted to evaluate pedestrians' impact on traffic conflicts between left-turning vehicles and opposing-through vehicles (V-V conflicts) as well as traffic conflicts between left-turning vehicles and pedestrians (V-P conflicts) in the permissive left-turn phasing scenario. Intersections with different opposing-through volumes, left-turn volumes, number of opposing-through lanes, and pedestrian volumes were modeled in VISSIM, a traffic micro-simulator. The surrogate safety assessment model (SSAM) was used to estimate the number of V-V and V-P conflicts. The effect of pedestrian presence on V-V and V-P conflicts was evaluated using simulation scenarios with and without pedestrian presence. Simulation results revealed that pedestrian presence increased both V-V and V-P conflicts. As pedestrian presence increased the total number of traffic conflicts, permissive left-turn phasing processed fewer left-turn vehicles to maintain the same level of intersection safety with pedestrian presence compared to the no-pedestrian scenario. Since current left-turn phasing decision guidelines do not consider the impacts of pedestrian presence, this research quantified pedestrian-influenced and pedestrian-involved left-turn traffic conflicts to determine appropriate left-turn signal phasing decisions to ensure safe and efficient crossing of pedestrians and vehicles at signalized intersections. This simulation-based study's findings can be beneficial in the decision making of left-turn phasing selection as the before-after intersection safety performance analysis by collecting field data often resources intensive.