THE METHODS DESCRIBED:

FLASHING YELLOW ARROW	INSERTED ALL-RED CLEAR
Signal display sequence (slow animation to show clearance periods) The Flashing Yellow Arrows method prevents yellow-trap by extending the period of the permissive turn until the lagging left-turn phase terminates. Thus, the permissive turn ends at the same time as the oncoming straight-ahead movement. A flashing yellow arrow keeps the adjacent straight-ahead movement (which has a red light) from falsely moving during this interval. Signal phase order (fast animation)	Signal display sequence (slow animation to show clearance periods) The Inserted Red Clearance method prevents yellow-trap by forcing the oncoming straight-ahead phase to terminate at the same time the oncoming permissive turn terminates. After a short all-red clearance to allow all left turns already waiting in the intersection to clear, the lagging turn phase and its concurrent straight-ahead movement are shown their green signals. Signal phase order (fast animation)
The basic Flashing Yellow Arrow method: Special signal faces are used for left-turn displays (see below). All heads with both permissive and protected left turns, plus all left-turn heads for oncoming traffic having permissive left turns, must have special signal faces. The basic flashing-arrow signal head displays the same aspects as the oncoming straight-ahead signals, unless a left turn phase for those turning drivers replaces the permissive display. The wiring for this system requires special lamp driver circuitry to flash the yellow arrow and darken the permissive display when the protected phase is active. Signal installations will also need extra lamp circuits per span wire or mast arm, since there are more signal indications facing in each direction. The change in the MUTCD (Manual of Uniform Traffic Control Devices) definition of a flashing yellow arrow was made in the 2009 MUTCD. A circular yellow is used to terminate the flashing yellow arrow, so it is quite evident that termination is taking place. Unlike the Dallas left turn, this method does not require screening the left turn signal head from adjacent straight-ahead traffic. This is the most promising solution to the problem.	The basic Inserted Red Clearance method: No special signal faces are needed. Special dummy phases are needed to make this work. This means that a standard 8-phase signal controller can not be used for a full quad split lead installation using this method. The signal display methods and wiring are the standard displays used in conventional installations. Special actuation circuits are needed for the dummy phases. Other wiring for this system is standard. A special phase sequence must be designed for every phase order this method is used for. No changes are needed in the MUTCD (Manual of Uniform Traffic Control Devices) for the method. Because the lagging through movement is interrupted, this is not a good yellow-trap solution for lead-lag phasing used for widening the progression-through-band at locations away from platoon crossing points.
Flashing Yellow Arrows sample installation data: The lagging left turn shown above as it would be installed. A visual example of flashing yellow arrows. Flashing Yellow Arrows in a quad split lead signal. Flashing Yellow Arrows in a quad single-split lead-lag signal. For comparison: A standard quad split lead left-turn signal causing yellow-trap. Flashing Yellow Arrows links: Flashing Yellow Arrows website Dallas left-turn phasing	Inserted Red Clear sample installation data: The lagging left turn shown above as it would be installed. Inserted Red Clear in a quad split lead signal. For comparison: A standard quad split lead left-turn signal causing yellow-trap.
CALL REDIRECTION	FALSE CALL INSERTION
Signal phase order (fast animation)	Signal phase order (fast animation)
The basic Call Redirection method: Standard signal faces are used for all displays. Detector calls to a left turn phase are redirected to the adjacent straight-ahead phase when the oncoming straight-ahead phase is active (displaying a green or yellow signal, or timing a red clearance). This prevents the left-turn phases from activating while both straight-ahead phases are active. Many signal controllers already have this feature, which is activated by setting bits in the PROM. No changes are needed in the MUTCD (Manual of Uniform Traffic Control Devices) for this method. This method will not work with any signal phasings other than leading left turns. Call Inhibit is similar to Call Redirection, except that the call is totally ignored, instead of being redirected. This can be used if the inhibited movement already has a circular green. But it removes dilemma-zone protection from the inhibited movement.	The basic False Call Insertion method: Standard signal faces are used for all displays. Detector calls to a left turn phase are also sent to the calling-detector input of any phase on the other street. This involves connecting a wire from the terminal where the left turn detector is connected to its own phase to the calling-detector input of a cross-street phase. This requires a cross-street phase to display before the left turn phase. If there are no active calls on the cross-street phase, it will use the minimum-green time and then terminate. No changes are needed in the MUTCD (Manual of Uniform Traffic Control Devices) for this method. This method will not work with any signal phasings other than leading left turns.
Call Redirection sample installation data: The leading left turn shown above as it would be installed. Call Redirection in a quad split lead signal. For comparison: A standard quad split lead left-turn signal causing yellow-trap. Call Redirection and Call Inhibit links: How to Inhibit Phases to Avoid Yellow Trap.	False Call Insertion sample installation data: The leading left turn shown above as it would be installed. False Calls implemented in a quad split lead signal. For comparison: A standard quad split lead left-turn signal causing yellow-trap.

SIGNAL FACES

Signal faces used with these methods
Standard signal faces
This three-section left-turn face is for left turns that are protected, but not permitted through gaps in oncoming traffic. It must now have a red arrow instead of a circular red.		This five-section left turn face is used for left turns that are protected during parts of the cycle and are also permitted through gaps in oncoming traffic on a circular green. Red arrows are not permitted in this face. This face can cause yellow-trap.		This three-section signal face is used for straight-ahead and right turn movements, and for left turns without protected phasing. These left turns are permitted on a circular green through gaps in oncoming traffic. This face can cause yellow-trap when it controls left turns.
Special signal faces
This signal face is for the Flashing Yellow Arrows protected and permissive display for preventing yellow-trap. The green arrow controls the protected left turn. The lower yellow arrow flashes to allow the permissive turn. The upper yellow arrow clears the flashing yellow arrow or the green arrow, and is used for the intersection flashing mode. But a flashing yellow arrow terminated by a steady yellow arrow might not be noticed by drivers at night, causing a hazard. See this effect here.			This signal face is for the Flashing Yellow Arrows permissive display for preventing yellow-trap. This signal face is used when the permissive left turn does not begin or end at the same time as the parallel straight-ahead phase. The bottom yellow arrow flashes for the permissive turn. The middle yellow arrow clears the flashing yellow arrow, to show that the flashing yellow arrow is ending. It has the same effect mentioned on the left.
This signal face is for the Flashing Yellow Arrows protected and permissive display for preventing yellow-trap. The left half of the signal face controls the protected left turn. The right half controls the permissive turn. The yellow arrow on the right flashes for the permissive turn. The circular yellow clears the flashing yellow arrow, to make it clear that the flashing yellow arrow is ending. This face does not conform to the MUTCD.			This signal face is for the Flashing Yellow Arrows protected and permissive display for preventing yellow-trap. The green arrow controls the protected left turn. The yellow arrow flashes to control the permissive turn. The circular yellow clears the flashing yellow arrow, to make it clear that the flashing yellow arrow is ending. It also clears the green arrow, and is used for the intersection flashing mode. It is safer than the MUTCD approved face, but it is not approved.
Signal meanings used with these methods
The meaning of a flashing yellow arrow had to be changed in the Manual of Uniform Traffic Control Devices, in order to provide a turn indication that means "yield to conflicting traffic." Then the individual states had to pass laws redefining the flashing yellow arrow, and update their uniform traffic control device manuals to reflect the change. The current status of each state can be found here: The Box Scores

Remember these facts:

1. Without left turn phases, 5 or more legs, odd geometries, or preemptions, yellow-trap does not exist.
2. If only one left turn is possible from a given street, yellow-trap cannot happen.
3. If both left turns from a given street are on the same phase, yellow-trap cannot happen.
4. If each leg of the street has its own exclusive phase (split phase), yellow-trap cannot happen.
5. Yellow-trap occurs where left turns are allowed to filter through gaps in oncoming traffic, and that circular green is terminated earlier than the oncoming green.
6. 3-section left turn faces remove yellow-trap from a street only if no left turns are permitted on circular greens from either direction on that street. If both left turns have 3-section faces, that is sufficient to prevent yellow-trap.
7. Flashing Yellow Arrows prevent yellow-trap by ending the permissive turn at the same time as the oncoming green. They work with almost any street and phasing configuration, and any form of logic (nonactuated, recall, locking, or nonlocking).
8. Call redirection works only on leading, actuated, nonlocking left turn phases.
9. CAUTION: Recalling a left turn phase (e.g. in the event of detector failure) defeats the protection of call redirection.
10. Dummy phase and cross street recall work with only leading left turn phases, but the left turn phases can have any form of logic (nonactuated, recall, locking, or nonlocking).
11. A single lag yellow trap has only five remedies:
    • Flashing Yellow Arrows.
    • Inserted All-Red Clearance.
    • Change to a leading turn phase.
    • Convert to a dual left turn phasing.
    • Prohibit or divert the oncoming left turn.
12. The type of left turn signal face, important to preventing yellow-trap in dual and quad left turn phasing, has no effect on yellow-trap in single left turn phasing. With an unmodified single left turn, the trapped left turn doesn't have a left-turn signal.
13. Sometimes diverting turns works better than extra turn phases.
14. Hidden clearance intervals have been banned for 10 years, yet there are still some around. Every green turn arrow must now be cleared with a yellow arrow.

These methods serve to prevent yellow-trap from occurring at traffic signals with turn arrows or preemption. They MUST be used to prevent the accidents that can occur otherwise. Failure to use them can lead to liability for accidents caused by yellow trap.

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