Traffic Signal Controller Output Channel Capacity Planning
Introduction
Picking the wrong controller output capacity means either wasted budget on a too-large controller or a forced replacement within five years. This guide shows how to count the outputs your intersection needs, add the right amount of spare, and pick the correct GAOQIAO controller.
Counting Outputs by Intersection Type
A 3-leg T-intersection with no turn arrows uses roughly 8-10 outputs: 3 vehicle phases (one per leg) plus pedestrian phases for the two side-road crossings. A 4-leg intersection with protected left turns on two approaches uses 18-22 outputs. A 4-leg intersection with protected lefts on all four approaches plus pedestrian phases and bicycle signals uses 28-32 outputs. A complex intersection with arrows, transit signals and preemption can use 40+ outputs.
The rule of thumb: count every red, yellow and green separately for every signal head, including pedestrian heads and bicycle signals. Arrow heads count as another full phase (3 outputs each).
Spare Capacity Rules
Always leave 15-20% spare capacity for:
- Future turn arrows after a traffic study
- New pedestrian or bicycle phases
- Detector expansion
- Preemption for emergency vehicles
- Replacement of a damaged output channel
If your design uses 30 outputs, specify a 44-output controller, not a 22. If your design uses 18, a 22-output controller is fine. The cost difference between controller sizes is small compared to the cost of replacing an undersized controller later.
Common Pitfalls
Three pitfalls to avoid:
1. Forgetting overlap phases: protected left turns often need an overlap phase (4 outputs) that runs with the opposing through movement. Skipping this in the count leaves the controller one output short on day one. 2. Not counting pedestrian and bicycle separately: a 3-aspect pedestrian head uses 2 outputs (red man, green man), not 1. Count by lamp, not by head. 3. Counting the same head twice: a 4-aspect head with arrow uses 6 outputs (red, yellow, green for ball + red, yellow, green for arrow), not 4.
Featured Products
Browse GAOQIAO's 22-output controllers, 56-output controllers, and the controller output guide.
Conclusion
Count by lamp. Add 15-20% spare. Pick the next size up. GAOQIAO supplies 22, 44 and 56 output controllers to match any intersection. Send us your signal head schedule and we will return a sized controller quotation.
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Frequently Asked Questions
What is the smallest controller GAOQIAO sells?
The 6-output fixed-time controller for very small sites. Most intersections need at least 22 outputs.
Can I expand a 22-output controller later?
No, the output panel, conflict monitor and detector rack are sized to the controller. Specify the next size at the start.
What is the largest controller you supply?
56 outputs in a single GAOQIAO controller, expandable via output panels for very large intersections.
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.