METHODOLOGY

The 166 FYA intersections were evaluated in three treatment categories: Category 1: 3-way intersections with one FYA approach; Category 2: 4-way intersections with one FYA approach; and Category 3: 4-way intersections with two or more FYA approaches. Crash data was analyzed according to average annual before and after by crash type, as well as the KABCO injury scale. Vehicle crashes were categorized as total crashes, injury crashes, property damage only (PDO) crashes, rear-end crashes, angle crashes, single vehicle crashes, head-on crashes, left-turn (LT) crashes, and left-turn-opposing-through (LTOT) crashes. the before/after crashes were also reported in equivalent property damage only (EPDO) values.

Societal economic costs per injury level were calculated based on an FHWA report and have been normalized to represent Massachusetts dollars, which is referred to as “MassDOT Economic Costs (Adjusted)”. The benefits from FYA implementation were determined by calculating the crash costs allocated during the before and after periods across each injury type within all the FYA treatment categories. The FYA installation costs were derived from various sources, such as a combination of previous FYA literature [1][2], MassDOT contractual records and construction estimates, and a survey of local transportation consultants. The economic expected lifespan of improvement is assumed to be 20 years, with an interest rate of 15 percent and no annual maintenance of FYA installation. Lastly, benefit-cost (BC) ratios were derived by taking into consideration the expected lifespan of the FYA installations and their expected annual cost. 

FINDINGS

• Treatment Categories 2 and 3 showed a statistically significant reduction (14.1 and 26.5 percent, respectively) in injury-related crashes, but all three categories had significant increases in rear-end crashes, which suggests the potential for stronger yield perception from drivers.
• LTOT-related crash rates were significantly reduced by 18.6 percent in Treatment Category 3.
• Treatment Categories 2 and 3 significantly reduced EPDO crashes by 11.7 and 22.1 percent; however, Treatment Category 1 resulted in a slight increase (three percent) of EPDO crashes.
• The 3-way FYA intersections (Treatment Category 1) yielded the highest BC ratio range (180:1 to 22:1). There was a significant benefit from the implementation of a FYA indication at these intersections.
• The 4-way intersections with multiple FYA approaches (Treatment Category 3) yielded a BC ratio range 22:1 to 3:1.
• Overall, the aggregated FYA BC ratios using the MassDOT adjusted costs ranged from 187:1 to 11:1.
• Overall, the results indicated strong evidence that the FYA reduced the average annual number of injury-related crashes, and ultimately led to a lower economic cost of injuries at all three of the treatment types evaluated in this study.

REFERENCES

[1] Schattler, K. L., E. Anderson, and T. Hanson. Safety Evaluation of Flashing Yellow Arrows for Protected/Permissive Left-Turn Control. Report FHWA-ICT-16-010. Illinois Center for Transportation, University of Illinois at Urbana–Champaign, Rantoul, 2016

[2] Srinivasan, R., B. Lan, D. Carter, S. Smith, S., and K. Signor. Safety Evaluation of Flashing Yellow Arrow at Signalized Intersections. Publication FHWA-HRT-19-036. Federal Highway Administration, Office of Safety Research and Development, McLean, VA, 2020.