Correctly installed, Flashing Yellow Arrows (FYA) can make an intersection much safer by preventing the hazard known as Yellow Trap. But incorrect installation can cause yellow trap and make the intersection more dangerous.

The following rules must be followed:

  1. A Flashing Yellow Arrow face (FYA) shall not be used if any of the following conditions exist:
  2. A Flashing Yellow Arrow face should not be used if any of the following conditions exist:
  3. If FYA exists on a road with left turns in both directions, FYA faces must exist in BOTH directions.
  4. Each FYA must be flashing at ALL TIMES when the ONCOMING circular green is lighted.
  5. Only one lens of the Flashing Yellow Arrow signal face may be lighted at any one time.
  6. The proper change intervals must be displayed on each signal face, as specified in the MUTCD:
  7. The instructions for flashing yellow arrows in the manuals for the signal controller and conflict monitor must be strictly followed.

The signal must be checked for yellow trap:

Look for any case where a circular green is displayed in one direction while the oncoming traffic has only steady red and/or steady yellow indications.

FYA signals

Correctly Installed - Safe - No Yellow Trap

yellow trap fya

Yellow Trap from Wrongly Installed FYA

If the circular signals in the two images above are not synchronized, refresh this page or open it in a new tab.

Notice that the lower diagram turns all of the signals on the leading side yellow and then red simultaneously. This is the yellow trap. A left turning driver on the leading side is trapped. The correct installation (top) keeps the yellow arrow flashing until the oncoming circular green turns yellow.

The bottom image above simulates what happens when FYA is wrongly linked to the adjacent circular green instead of the oncoming circular green. It brings the wrong timing of left turns on circular green to the FYA, causing yellow trap. Notice the bottom diagram above has the same indications the diagram below has. Both cause yellow trap.


yellow trap signals

Yellow Trap from Left Turns on Circular Green

The problem is that the circular green controls too many movements to be used safely when left turns are controlled separately. It gives an indication to turn left permissively, as well as a go for straight-ahead and right turning traffic. This means that it can't be used as a left turn indication in a lead-lag signal.