Flashing Yellow Arrow (FYA) left-turn signal indications have seen increasingly widespread use since their adoption into the Manual on Uniform Traffic Control Devices as a standard treatment in 2009. FYA indications offer benefits both in terms of improved safety and efficiency. The greatest benefit of FYA indications is that left turn phasing can be varied by time of day to respond to varying traffic demands, which reduces delay. For example, FYA indications may be used to allow protected-only phasing during peak periods and permissive-only phasing during off-peak periods. Studies have shown that having a dedicated left arrow indication for left turning movements is better understood and obeyed by the driving public, leading to fewer crashes. For these reasons, agencies nationwide are installing FYA indications on new traffic signal installations and retrofitting existing traffic signals with FYA.
The City of Plymouth commissioned a study to evaluate and prioritize 70 signalized intersections for flashing yellow arrows. The study required an intense data collection effort spread across multiple agencies that own and operate traffic signals within the City. Each intersection was broken down by movement and evaluated for feasibility of FYA. Movements that passed the initial screening were evaluated using criteria to estimate the amount of benefit and assigned a relative benefit score. Planning-level cost estimates were prepared for each intersection that had FYA eligible movements. A method was developed to rank each intersection based on cost and potential benefit.
In the final step of the study, SRF developed a three-year phasing plan for implementation based on intersection rankings, geographical areas of the City, and the City’s available CIP funds per year.