United States Department of Transportation
i
Evaluating the Safety Impacts of Flashing Yellow Permissive Left-Turn Indications in Massachusetts
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2021-03-01
[PDF-6.10 MB]
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Edition:Final Report: March 2021 [Dec. 2019–March 2021]
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Abstract:The 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD) introduced the flashing yellow arrow (FYA) as a permissive left-turn indication. Massachusetts recently implemented this novel traffic control device through a statewide retrofitting project at over 350 traditional protected-permissive left-turn traffic signals. A before/after implementation safety impact analysis was conducted, including a thorough benefit-to-cost analysis. The analysis evaluated the economic benefits of installing FYA signals, yielding a range of benefit-to-cost ratios across the three FYA treatment intersections (3-way with one FYA, 4-way with one FYA, and 4-way with two-or-more FYAs). Crashes were annualized per year using the FHWA KABCO injury scale, with economic costs per injury level calculated using Massachusetts adjusted FHWA costs (“MassDOT Economic Adjusted Costs”). In MassDOT adjusted costs, the 3-way FYA intersections yielded the highest BC ratio range (180:1 to 22:1) and 4-way intersections with multiple FYA approaches yielded the lowest (22:1 to 3:1). The economic benefits suggest that the FYA signal retrofits should be widely implemented, regardless of intersection type. Overall, results provided overwhelming evidence that the FYA reduced the average annual number of injury-related crashes and led to lower economic cost of injuries in all three of the treatment types of intersections investigated.
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