Methodology for Evaluating Intersection Safety & Operational Performance With Left-Turn Phasing
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2021-03-01
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Edition:Final Sept 2019 to March 2021
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Abstract:According to the National Highway Traffic Safety Administration (NHTSA), many fatal and severe injury crashes involve left-turn traffic. Based on the left-turn crash record from the Utah Department of Transportation (UDOT) during 2010-2017, 24,860 crashes involved left-turning vehicles, including 714 suspected serious injuries and 82 fatalities. Moreover, about 88% of them are angle incidents that sometimes cause severe crashes. Therefore, considering permitted left-turn phasing can lead to high crash risks, it is critical to investigate the need of adopting protected left-turn phasing at some intersections. This research project proposes a method to evaluate intersection safety and operational performance with different left-turn phasing treatments. For comparison purposes, the method also quantifies both crash and operational performance by US dollar equivalents. The overall analysis framework includes three core steps when considering a phase change from permitted to protected: 1) Estimate the safety benefit (i.e., reduced left-turn crash cost), 2) Calculate the operational cost (i.e., increased delay cost), and 3) Compute the benefit/cost (B/C) ratio and make the phasing design recommendation. For testing, the proposed method is implemented on four signalized intersections in Utah. The research outcomes could help UDOT make better decisions when facing the tradeoff between operational efficiency and intersection safety in left-turn phasing designs.
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