Safety effects of traffic signing for left turn flashing yellow arrow signals

•In 2010, the left turn flashing yellow arrow signal displays were installed at signalized intersections on state routes in the Peoria, Illinois, area. Supplemental traffic signs with text “Left Turn Yield on Flashing Yellow Arrow” were mounted on the mast arm adjacent to the left turn signal at over half of the FYA installations.•The purpose of this paper is to present the results of the effectiveness evaluation of the FYA supplemental sign on safety, for drivers of all ages and for older drivers.•A crash-based comparison of 164 FYA approaches including 90 approaches with the sign and 74 approaches without the sign showed greater crash reductions when the supplemental FYA sign was present.•The results also showed that crashes involving drivers age 65 and older did not experience the same magnitudes of crash reductions as compared to all drivers.•Based on the findings of this research, it is recommended that supplemental signs be used when initially implementing the FYA, and that effort to educate the driving public on new traffic control be made to further improve safety at signalized intersections. In 2010, the left turn flashing yellow arrow (FYA) signal displays were installed at signalized intersections on state routes in the Peoria, Illinois, area. Supplemental traffic signs with text “Left Turn Yield on Flashing Yellow Arrow” were mounted on the mast arm adjacent to the left turn signal at over half of the FYA installations. The purpose of this paper is to present the results of the effectiveness evaluation of the FYA supplemental sign on safety. Analyses are presented on the effects of the FYA supplemental sign for all drivers and a subset of drivers age 65 and older. A crash-based comparison of 164 FYA approaches including 90 approaches with the sign and 74 approaches without the sign showed greater crash reductions when the supplemental FYA sign was present. The results also showed that crashes involving drivers age 65 and older did not experience the same magnitudes of crash reductions as compared to all drivers. The findings of this research indicate that supplemental FYA signs may help in improving safety for left-turning vehicles during the permissive interval. Thus, it is recommended that supplemental signs be used when initially implementing the FYA, and that effort to educate the driving public on new traffic control be made to further improve safety at signalized intersections.