United States Department of Transportation
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Development of Guidelines for Implementation of Contraflow Left-Turn Lanes at Signalized Intersections
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2020-08-01
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Edition:Final Report
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Abstract:An innovative intersection design, Contraflow left-turn lane (CLL), designed for increasing the left-turn capacity has been increasingly implemented at the signalized intersections. This study developed a systematic method for determining the length of CLL and the signal timing plan for implementing CLL at signalized intersections. The signal timing and geometric design requirements in the implementation of CLL have been discussed and thoroughly considered in developing the proposed method. First, the development of the signal timing plan has considered both the pre-clearance time required before the start of the pre-signal phase and the clearance time required at the end of the pre-signal phase. As a result, it will reduce the risks associated with the use of CLL, and make CLL a safety solution to mitigate traffic congestion at signalized intersections. Second, the method for estimating the length of CLL is based on the conditions for maximizing the utilization of CLL. As a result, the estimated CLL lengths will allow the CLL intersection to achieve its best operational performance. A case study was conducted for validating the operational benefits of redesigning a real-world CLL intersection using the signal timing plan and CLL lengths recommended by the proposed method. The traffic simulation results show that the redesigned CLL intersection outperforms the existing CLL intersection in terms of the average traffic delay, average vehicle travel time, and average queue length, and the CLL intersection can achieve its best performance at the recommended CLL lengths. These results verified that the method proposed by this study can provide useful tools and design guidelines to the traffic engineers in the implementation of the CLL intersection design.
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[PDF-1.78 MB]
