Safety and mobility effects of installing speed-humps within unconventional median U-turn intersections

Abstract

The main aim of this paper is to evaluate the effects of installing speed-humps on the safety and mobility of the unconventional median U-turn, three-leg intersections, using the VISSIM microscopic traffic simulation model. The average delay was used as the measure of mobility, while the simulated conflict ratio based on the time-to-collision (TTC) surrogate safety measure, was used as an indicator of safety performance. The surrogate safety assessment model (SSAM) was applied to extract traffic conflicts, with TTC ≤ 1.50 s, which represent less severe conflicts, and TTC ≤ 0.50 s, that represent severe conflicts. The results show that hump speeds of 5.0 km/h significantly increase the intersection average delay by 109–448% and severely increase traffic conflicts, regardless of the hump location. While hump speeds of 20.0 km/h increase the average delay by 2–36%, based on the traffic conditions. Moreover, the 20.0 km/h humps could potentially reduce serve conflicts by about 11–20%.