Arrow Signal Head Configuration Guide for Protected Left Turns
Introduction
An arrow signal head shows drivers which movement is protected. The right arrow configuration keeps drivers in the correct lane, prevents wrong-way turns and reduces angle crashes. This guide covers the standard configurations used on protected left turns.
4-Aspect vs 5-Aspect Arrow Heads
A protected left turn uses a 4-aspect arrow head: red arrow, yellow arrow, green arrow and a yellow trap-avoidance display. The 4-aspect format prevents the "yellow trap" where a driver in the left turn lane sees a yellow ball on the adjacent through lane and assumes the protected left is also ending.
A 5-aspect arrow head adds a circular green to indicate that the left turn is now permissive (yield to oncoming traffic). Use 5-aspect when the same lane serves both protected and permissive left turns during different times of day.
Mounting Position
The arrow head mounts in line with the left turn lane, at the far side of the intersection for head-on visibility. For a protected-only left turn, place the arrow directly over the lane center. For a protected/permissive combo, the arrow is offset to the left side of the lane.
GAOQIAO supplies 4-aspect and 5-aspect arrow heads in 200mm, 300mm and 400mm diameters, with bi-directional arrow lenses available for median-running left turn lanes.
Phasing
The protected left turn phase is paired with the opposing through phase in a single ring. When the through phase runs, the left turn holds. When the left turn runs, the opposing through holds. The yellow trap is prevented by holding the through phase until the left turn phase ends (4-aspect arrow with circular red).
For protected/permissive operation, the controller runs the protected green arrow first, then drops to circular green for the permissive phase. GAOQIAO controllers support both modes.
Featured Products
GAOQIAO supplies 4-aspect arrow heads in all standard diameters. See the signal pole mounting guide for pole sizing.
Conclusion
A 4-aspect arrow head on every protected left turn, with the right mounting and phasing, prevents the yellow trap and reduces angle crashes. GAOQIAO arrow heads are MUTCD-compliant and ship with documented lens options. Send us your intersection layout for a turn phase plan.
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Frequently Asked Questions
Can I use a 3-aspect arrow head for a protected left turn?
No. 3-aspect arrow heads are for permissive left turns only. Protected left turns need 4-aspect (with circular red) or 5-aspect (with circular green) to avoid the yellow trap.
What diameter arrow head should I use?
Match the diameter to the vehicle signal head in the same intersection. A 300mm vehicle signal with a 200mm arrow looks unbalanced.
Do I need a bi-directional arrow head?
Only for median-running left turn lanes where drivers in either direction can use the lane. A standard left turn lane uses a single-direction arrow.
Relevant GAOQIAO products
These public GAOQIAO catalogue pages are related to the guide. Open them for the representative description, then confirm the latest drawing and configuration before ordering.
- Traffic signal controllersWired and solar controllers with 6, 22, 44 and 56 output options.
- LED traffic signal heads200mm, 300mm and 400mm signal heads with MUTCD, EN12368, GB14886 compliance.
- Signal polesVertical, signal arm and double-arm poles for any intersection geometry.
- Spare parts and accessoriesSpare LED modules, lenses, visors, surge arrestors and anchor bolts.