Capacity of Median U-Turns Using Traffic Simulation
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Capacity of Median U-Turns Using Traffic Simulation Jalal T. S. Al-Obaedi 1 Received: 11 September 2019 / Revised: 9 October 2020 / Accepted: 22 October 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract 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. Keywords Microsimulation . Traffic calming . U-turn . Speed humps . Capacity
1 Introduction 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 through and opposing traffic. The driving rules at the U-turn sites forces U-turn drivers to slowdown and even to stop and wait appropriate gaps within opposing direction. Some U-turn sites has an auxiliary lane prior to the U-turn sites to provide storage area and to minimize the effect of the turning traffic on the through traffic. Another benefit regarding the use of such auxiliary lane is to reduce accident rates at U-turn’s locations [1, 2]. To enhance traffic safety at median U-turn sites, speed humps were installed as a type of traffic calming to force the incoming (opposing), traffic that conflict with the turning traffic, to reduce their speeds [3]. The * Jalal T. S. Al-Obaedi [email protected] 1
Roads and Transport Department, College of Engineering, University of Al-Qadisiyah, Al-Diwaniyah, Iraq
speeds hump is a raised obstruction installed over the highways pavement across the whole lanes [4]. Figure 1 shows a graph illustrating the typical layout of the Uturn sites, traffic movements and the location of a speeds hump. Some previous research has considered the effect of speed humps as presented in Table 1. The findings show some benefits in reducing accident rates and its hazard. The negative impact represented by i
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