Flashing Yellow Arrows

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The City of Flagstaff’s Transportation Program will be making traffic control changes to intersections along Beulah Boulevard. The intersection of McConnell and Beulah will shortly have flashing yellow arrows for all left turn movements. The intersections of Forest Meadows and Beulah and Woodlands Village and Beulah will also have flashing yellow arrows. There are also plans for many changes at the intersection of Lake Mary and Beulah. These changes include making dual right-turn movements for the westbound approach, adding flashing yellow left-turn arrows to each movement, designating the northbound through/right lane into a right-turn only lane, making the southbound left-turns permitted/protected, changing all of the left-turns to a lagging phase operation, and replacing all of the effected signal heads and cabinet with newer equipment.

Flashing Yellow Arrows:

The City will install flashing yellow arrows at all intersections listed above. Flashing yellow arrows will replace the green ball on permissive left-turn movements. Permissive movements are when the green arrow is not used and vehicles yield to conflicting traffic and pedestrians, and then proceed, when safe, on a green ball. The flashing yellow arrow will work as a yield for turning movements. Drivers may turn on a flashing yellow arrow, but must first yield to oncoming traffic and pedestrians and then proceed through the intersection with caution. Drivers have previously mistaken the green ball indication above a left-turn lane to mean “GO”, when it actually means yield. The flashing yellow arrow is a more intuitive color and symbol of yield, over the traditional green ball. According to the NCHRP Report 493, the flashing yellow arrow display offered the highest level of safety. Also, left-turn traps are completely eliminated when the flashing yellow left-turn arrow is tied to the opposing through green indication. A left-turn trap occurs when a driver is making a left on a permissive phase and then becomes trapped in the intersection while the light turns yellow. The driver sees that the adjacent through traffic also receives a yellow light and assumes the same for the opposing through. The driver then proceeds through the intersection, possibly causing a T-bone type crash. The flashing yellow arrow offers better driver recognition and eliminates left turn traps, all resulting in a safer intersection. New signs will be placed near the signals on the mast arms informing drivers how to handle the unfamiliar signal head.

Left-Turns Permitted/Protected:

Currently, the southbound movements at Beulah and Lake Mary and the westbound movements at Beulah and Forest Meadows left-turn lanes run as a protected-only phase, but with the addition of the yellow flashing arrows these movements will also become permissive. This change from a protected-only phasing to protected-permitted, with the flashing yellow arrows, will allow this movement to operate much more efficiently, while still keeping the intersection safe.

Left-Turns Lagging:

At the intersection of Beulah and Lake Mary the eastbound left-turn movement, coming out of the University Heights neighborhood, currently runs as a leading phase. In this case, a leading phase means that the eastbound and westbound left-turn phases go together, followed by the east and west bound through movements. It is planned to change the eastbound left-turn to a lagging phase, which means that the westbound through and left will start with green, followed by the eastbound through and left. This change is expected to increase efficiency of the intersection by allowing many of the eastbound left-turn vehicles to turn on the permissive phase, and then clear out the remaining queue during the protected phase.
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