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Investigating the Conversion of a Signalized Intersection to a Turbo Roundabout
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2025-03-01
[PDF-4.74 MB]
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Corporate Contributors:State of California SB1 2017/2018, Trustees of the California State University Sponsored Programs Administration ; United States. Department of Transportation. University Transportation Centers (UTC) Program ; United States. Department of Transportation. Office of the Assistant Secretary for Research and Technology
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Abstract:Turbo roundabouts are multilane roundabouts with helical pavement markings and raised structures. While they have seen widespread use in Europe, California is only the second state in the U.S. (after Florida) to have installed a turbo roundabout. Turbo roundabouts separate the ingress and circulating roadways. The concept was proposed and implemented in the Netherlands to mitigate congestion by improving traffic flow efficiency and addressing safety concerns on conventional multilane roundabouts. This research evaluates the first-ever turbo roundabout in California and compares its safety and operational performance with the previously existing 4-legged signalized intersection. The research team obtained safety and operational performance measures using well-calibrated simulation models and video analytics of the real-world conditions recorded before and after the installation of the turbo roundabout. The safety metrics include surrogate safety measures defining traffic conflicts between vehicles that enabled a quicker safety evaluation compared to multi-year collision data. The results show that the turbo roundabout effectively reduced crash potential and queuing delays at this site, meaning smoother, safer traffic flows. The real-world conflict data shows that more severe crossing and head-on conflicts (situations that could lead to collisions) of the previous 4-legged signalized intersection have all but been eliminated.
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