CONTRIBUTION TO THE U-TURN DESIGN AT MEDIAN OPENINGS IN IRAQ: Al-NAJAF CITY AS A CASE STUDY

Al-Jameel, Hamid Athab · 2021 · Crossref

DOI: 10.30572/2018/kje/611311

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Summary

This study addresses the severe traffic congestion and safety issues associated with U-turn median openings in Al-Najaf City, Iraq. Field observations revealed that left-turning vehicles at these locations create significant bottlenecks on both origin and destination roads, often requiring traffic police to deploy temporary plastic barriers to separate turning vehicles from opposing through traffic. The research aims to introduce a new U-turn design that protects both turning and through traffic to improve performance and capacity. The methodology combines field data collection with microscopic traffic simulation. The author conducted field observations at multiple U-turn sites in Al-Najaf, including locations on the Kufa–Najaf and Najaf–Karbala roads. Data collected included traffic flow rates, vehicle composition (noting a 25% minibus and 5% truck average), and spacing distances between access points and U-turns. The study found that approximately 90% of observed U-turns did not meet recommended separation distance standards, contributing to accidents and congestion due to insufficient weaving lengths. To evaluate potential solutions, the author developed a simulation model using S-Paramics. This model was calibrated using field data from Al-Najaf and validated against published field data from Jordan to ensure accuracy in representing driver behavior and traffic streams. The study tested two new design scenarios against the conventional U-turn layout. The first proposed design featured a protected U-turn with a widened area to provide a refuge for turning vehicles. The second design allowed for a larger turning radius to facilitate heavy vehicle maneuvers, though it noted a potential increase in accident risk. Simulation results demonstrated that both new designs significantly outperformed the current conventional design. Specifically, the new designs increased U-turn capacity by more than two times that of the normal case. The simulations showed continuous movement for both U-turning and opposing traffic, eliminating the queuing issues observed in the field. The significance of this work lies in its application of simulation modeling to solve specific traffic congestion problems in Iraqi urban contexts. The findings suggest that simulation models are effective tools for evaluating traffic management strategies. The study concludes that the proposed protected U-turn designs are more efficient than conventional designs, offering higher capacity and reduced congestion. Additionally, the research highlights the need to improve the spacing between access points and U-turns to meet critical spacing standards, thereby reducing accidents and enhancing the capacity for both through and turning vehicles.

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• intersection design