What is yellow trap? Are FYA and circular green the same?
How can yellow trap be prevented? How must FYA be correctly installed?
How does FYA prevent yellow trap? How can FYA be incorrectly installed?
FYA - What can go wrong?

Many people don't understand the purpose of flashing yellow arrows (FYA) on traffic signals. Here are some questions and answers to help you understand them:

  • What's wrong with just using the circular green? We know what that means.

    Nobody can easily obtain the meaning shown at right using a circular green indication to indicate a permissive left turn.

    The display shown indicates:

    1. Straight and right turn indications are red, so those drivers must stop.
    2. The left turn is a permissive turn through gaps in oncoming traffic.

    The following capabilities are revealed:

    • The flashing yellow arrow can allow the permissive turn to be made while the straight ahead signals are red.
    • The circular green can't do that, because it also tells other movements to go.
circular red with fya

Special Movement With Flashing Yellow Arrows

  • Dallas Phasing:

    Dallas Phasing (also called the Dallas Display) was an attempt to use the circular green for a permissive left turn without causing yellow trap. It was installed in some states between 1992 and 2009.

    Dallas Phasing required vision-restricting louvers or optical programming on the circular green and circular yellow in the left turn signal, to keep drivers going straight or right from seeing them. This was intended to keep from confusing straight-ahead drivers.

    Drivers turning left had trouble understanding this display. Many didn't understand the meaning of the one circular green light and two circular red lights they saw. Also, Dallas Phasing can't be used on span wires without the wind twisting the signals, showing the hidden signals to the wrong drivers.

    The 2003 Manual on Uniform Traffic Control Devices (MUTCD) approved Dallas Phasing, but the 2009 MUTCD prohibits it in favor of flashing yellow arrows.

Dallas Phasing display

This display is the Dallas Phasing equivalent to the flashing yellow arrow display shown above, as seen by a left-turning driver.


The following are ways to prevent yellow trap:

  1. Yellow trap can not occur at a T intersection.*
  2. Yellow trap can not occur if either street is one-way through a 4-way intersection.*
  3. Have no left turn phases or pre-emptions on the street.
  4. Never end circular greens on the same street at different times.
  5. Make all left turns exclusively protected.
  6. Lock the signal controller so it can't display a green left turn arrow immediately after an oncoming circular green.*
  7. Prohibit the left turn from the direction opposite to the left turn signal.
  8. Install special circuitry in the signal controller to keep it from skipping phases into yellow trap.*
  9. Use flashing yellow arrow signals.†
  10. Use a flashing red arrow for the same purpose, with the same timings the flashing yellow arrow uses.†
    * A pre-emption can still cause yellow trap.
    † A wrongly-configured pre-emption can cause yellow trap.


The following rules must be followed:

  1. Flashing yellow arrows may not be used if a left turn lane is shared with another movement.
  2. If a flashing yellow arrow face is installed on one leg of a road, FYA faces must ordinarily be installed on both legs of the same road.

    Exceptions are cases where a one-way street or a T intersection makes the left turn in the opposite direction nonexistent.

  3. Each flashing yellow arrow must be flashing at ANY time when the oncoming circular green is lighted.

    The flashing yellow arrow must NEVER be connected to flash whenever the circular green on the same leg is lighted (it must be connected to the circular green on the oncoming leg) unless the leg is the stem of a T intersection.

  4. Only one lens of the flashing yellow arrow signal face may be lighted at any one time.
  5. The proper yellow and red change intervals must be displayed on each flashing yellow arrow face, as specified in the MUTCD:
    • The steady yellow arrow must accompany any change from flashing yellow arrow to red arrow.
    • The steady red arrow may follow the steady yellow arrow in the red change period.
    • The steady yellow arrow must not accompany any change from flashing yellow arrow to green arrow.
    • The flashing yellow arrow must continue to flash during the entire change interval before the green arrow.
  6. The display on the flashing yellow arrow face must correspond to the display on the oncoming circular faces:
    Arrow Face
    Flashing YellowGreen
    Flashing Yellow
    to Steady Yellow*
    Green to
    Steady GreenRed
    Steady Green to
    Steady Yellow
    Stay Red
    Steady RedRed

    * Both must always change together

  7. The instructions for flashing yellow arrows in the manuals for the signal controller and conflict monitor must be followed.