Capacity of Median U-Turns Using Traffic Simulation

Median U-turn has been widely used at Iraqi highways and regards as one of sources of traffic congestion creation due to the fact the U-turn movements conflict with traffic at the origin and destination directions. To enhance traffic safety at U-turn sites, speed humps were installed to force speed reduction to the incoming traffic that conflicting with the turning traffic. This paper used real data taken from four median U-turn sites. Three of these sites has speed humps while the fourth is not. VISSIM traffic simulator has been used to build simulations models that could replicate the real site movements. The observations of traffic data for these sites have been conducted using video recordings to obtain traffic parameters contains traffic volumes and the time spent for tuning process. The simulation results based on traffic volumes and average time spent (ATS) for turning has been compared with the real data based on calibration and validation processes and good agreements have been obtained. The developed simulation models were used to examine different scenarios affecting the capacity of the U-turn traffic. The results suggested that the capacity is increased with the decreasing of speeds of opposing traffic and also with decreasing the distance between a speeds hump and the U-turn location.