PREVENT YELLOW TRAP
DURING CONSTRUCTION
Construction work often causes unusual problems with signalized intersections. Here is a list of hazards and
MUTCD violations caused by construction activities:
RULES FOR LEFT TURN LANE CLOSURES:
- ALWAYS check to make sure that recalling a phase with a disconnected (dug up) detector will not cause yellow trap.
- ALWAYS terminate opposite circular greens simultaneously if left turns are permissive on circular green.
- ALWAYS check all possible combinations of phase skip for yellow trap.
- ALWAYS check for yellow trap on the approach opposite to the approach with the left turn signal.
- Check traffic conditions other than left turn phases. Make sure they do not cause yellow trap.
- Check existing pre-emptions (for emergency vehicles, railroads, lift bridges, queue
discharge, etc.) for yellow trap.
- Traffic signal phasing must be altered when left turn and thru movements share the same lane as a result:
The flashing yellow arrow face is normally not allowed.
- Interpretation 4(09)-15 (I) allows a 5-section signal face to have 6 indications with a dual color arrow section
for variable left turn modes with a shared thru/left lane. The flashing yellow arrow is in the dual arrow section.
This could be extended to a construction zone, especially if the left turn mode can change.
- The flashing red arrow face is normally not allowed.
-
Interpretation 4(09)-15 (I) could be extended to allowing a 5-section signal face to have a flashing red arrow
for a temporary shared lane.
- A green left turn arrow may not be displayed while the thru signals are yellow or red.
- The following phasings are not suitable:
- single lag (on the side opposite the side of the lane closure)
- simultaneous lead
- split lead phasing
- simultaneous lag
- split lag
- Any phasing where a flashing yellow arrow is used to prevent yellow trap on the leg with the closure must
be carefully considered.
- Suitable phasings
- single lead on the side with the closure*
- single lead on the side opposite the closure*
- single lag (on the side of the lane closure)*
- split phasing (unsplit lead lag)
- split lead-lag with the closure on the lag side*
- alternating single lead (each leg gets a leading turn on alternating cycles)*
- make the left turn for the lane that closed exclusively permissive*
- prohibit the left turn for the lane that closed
* Be sure to prevent phase skip that could cause yellow trap. Do not allow permissive turns if
they end in yellow trap.
- Any nonconforming signal face must be taken down, or disconnected and hooded.
RULES FOR RIGHT TURN LANE CLOSURES
- ALWAYS check all right turn overlap phases for yellow trap.
- ALWAYS check all possible combinations of phase skip for yellow trap.
- ALWAYS check for yellow trap on the approach opposite to any approach with a left turn signal.
- Check traffic conditions other than left turn phases. Make sure they do not cause yellow trap.
- Check existing pre-emptions for yellow trap.
- Traffic signal phasing must be altered when right turn and thru movements share the same lane as a result:
- The flashing yellow arrow face is not normally allowed for the right turn. But Interpretation 4(09)-15 (I) allows
a 5-section signal face with 6 indications that might work here.
- The flashing red arrow face is not normally allowed for the right turn. But Interpretation 4(09)-15 (I) allows a
5-section signal face that might work here.
- A green right turn arrow may not be displayed while the thru signals are yellow or red.
- The following phasings are not suitable:
- right turn simultaneous with cross street left turn
- right turn green arrow in conflict with oncoming permissive left
- continuous right turn
- Any phasing where a flashing yellow arrow is used to prevent yellow trap on the leg with the closure
must be carefully considered.
- Suitable phasings
- right turns allowed on circular green*
* Be sure to prevent phase skip that could cause yellow trap. Do not allow permissive turns if
they end in yellow trap.
- Any nonconforming signal face must be taken down, or disconnected and hooded.
RULES FOR CLOSURES WHERE ONLY A SINGLE LANE REMAINS APPROACHING THE INTERSECTION:
- ALWAYS check to make sure that recalling a phase with a disconnected (dug up) detector will not cause yellow trap.
- ALWAYS terminate opposite circular greens simultaneously if left turns are permissive on circular green.
- ALWAYS check all possible combinations of phase skip for yellow trap.
- ALWAYS check for yellow trap on the approach opposite to any approach with a left turn signal.
- Check traffic conditions other than left turn phases. Make sure they do not cause yellow trap.
- ALWAYS check all right turn overlap phases for yellow trap.
- Check existing pre-emptions for yellow trap.
- Traffic signal phasing must be altered when all movements share the same lane as a result:
- The flashing yellow arrow face is not normally allowed But Interpretation 4(09)-15 (I) allows a 5-section signal
face with 6 indications that might work here.
- The flashing red arrow face is not normally allowed But Interpretation 4(09)-15 (I) allows a 5-section signal face
that might work here.
- A green turn arrow may not be displayed while the thru signals are yellow or red.
- The following phasings are not suitable:
- single lag (on the side opposite the side of the lane closure)
- simultaneous lead
- split lead phasing
- simultaneous lag
- split lag
- right turn simultaneous with cross street left turn
- right turn green arrow in conflict with oncoming permissive left
- continuous right turn
- Any phasing where a flashing yellow arrow is used to prevent yellow trap on the leg with the closure
- Suitable phasings
- single lead on the side with the closure*
- single lead on the side opposite the closure*
- single lag (on the side of the lane closure)*
- split phasing (unsplit lead lag)
- split lead-lag with the closure on the lag side*
- alternating single lead (each leg gets a leading turn on alternating cycles)*
- make the turns for the lanes that closed exclusively permissive*
- prohibit the left turn for the lane that closed
- right turns allowed on circular green*
* Be sure to prevent phase skip that could cause yellow trap. Do not allow permissive turns if
they end in yellow trap.
- Any nonconforming signal face must be taken down, or disconnected and hooded.
RULES FOR CLOSURES WHERE ONLY A SINGLE LANE REMAINS DEPARTING THE INTERSECTION:
- ALWAYS check all right turn overlap phases for yellow trap.
- ALWAYS check all possible combinations of phase skip for yellow trap.
- ALWAYS check for yellow trap on the approach opposite to any approach with a left turn signal.
- Check traffic conditions other than left turn phases. Make sure they do not cause yellow trap.
- Check existing pre-emptions for yellow trap.
- Traffic signal phasing must be altered when right turn and thru movements share the same departure lane as a result:
- A green right turn arrow may not be displayed while the cross street thru signals are green.
- A flashing yellow right turn arrow may not be displayed while the cross street thru signals are green.
- The following phasings are not suitable:
- right turn simultaneous with cross street through movement
- right turn green arrow in conflict with oncoming permissive lefts
- continuous right turn
- Any phasing where a flashing yellow arrow is used to prevent yellow trap on the leg with the closure.
- Suitable phasings
- right turns allowed on circular green*
- right turns controlled by yield or stop sign
* Be sure to prevent phase skip that could cause yellow trap. Do not allow permissive turns if
they end in yellow trap.
- Any nonconforming signal face must be taken down, or disconnected and hooded.
RULES FOR WHERE A TEMPORARY RUNAROUND CREATES AN OFFSET INTERSECTION:
- It might be better, if real estate usage allows, to move both legs of the intersection to the temporary location,
rather than creating an offset intersection.
- If the offset between the legs is as long as a city block, no special phasings are needed. Progression offsets
may need to be changed.
- If the offset between the legs is less than 60 feet, it might be better to create an oblique intersection and
operate it normally.
- Special phasing considerations where the traffic on the offset turns to the right first, and then to the left.
Phasings on the street that is not offset are more critical.
- With flashing yellow arrows, this street can have a single phase.
- A lagging left turn is efficient here. But it may not be a split lag unless flashing yellow arrows are used.
- If no left turn lanes exist, these legs must have separate phases (split phase).
- Provide adequate clearance time when leaving this street.
- Phasing the offset legs.
- If left turn lanes and flashing red arrows are used on the offset legs, and left turn lanes and red arrows are
used on the segment of the other street between the offset legs, then the offset street can have a single phase.
- The left turns from the offset street can have their own phase.
- If left turn lanes do not exist on the offset legs, or the left turn lanes do not provide enough left turn
storage, then each of the offset legs must have its own separate phase (split phase).
- If both streets require split phase, a clockwise or anticlockwise phasing is efficient.
- Special phasing considerations where the traffic on the offset turns to the left first, and then to the right.
Phasings on the street that is not offset are extremely critical here.
- With flashing yellow arrows and double clearance, this street can have a single phase.
- A lagging left turn is efficient here. But it may not be a split lag unless flashing yellow arrows are used.
- If no left turn lanes exist, these legs must have separate phases (split phase).
- Provide adequate clearance time when leaving this street.
- Phasing the offset legs.
- If signalized right turn lanes are used on the segment of the other street between the offset legs, then the
offset street can have a single phase.
- If the right turn lanes do not exist, or the thru lanes in the segment between the offset legs do not provide
enough storage for waiting traffic, then each of the offset legs must have its own phase (split phase).
- If both streets require split phase, a clockwise or anticlockwise phasing is efficient.
OTHER CONSIDERATIONS FOR TEMPORARY SIGNAL ALTERATIONS:
- Use the rules for flashing yellow arrows when designing flashing red arrows.
- ALWAYS check to make sure that recalling a phase with a disconnected (dug up) detector will not cause yellow
trap.
- The MUTCD no longer permits Dallas Phasing, flashing circular yellow, and flashing circular red for permissive
left turns. The changes necessitated for the construction might result in a requirement to permanently remove these
features.
- Use enough signs so the driver is informed of new lane use assignments.
- If lanes are moved to the right or the left, signal heads (especially left turn heads) need to be moved so they
are over the correct lanes.
- Use the rules for flashing yellow arrows with any legacy instances of these prohibited systems too.
- Check all possible combinations of phase skip for yellow trap.
- Check traffic conditions other than left turn phases. Make sure they do not cause yellow trap.
- Make sure changing a one-way road to a two way road does not cause a new yellow trap.
- Check for yellow trap on the approach opposite to the approach with the left turn SIGNAL.
- Where a left turn lane exists, use the flashing yellow arrow permissive signal to remove yellow trap from
approaches without protected turns.
- Check for Second Yellow Trap and Third Yellow Trap.
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