How to Specify a Traffic Signal Head: Size, Sections and Indications
A traffic signal head may look like a simple red, yellow and green assembly. For a project buyer, however, the correct configuration is the result of several linked decisions: the viewing distance, road geometry, lane movements, local signal rules, mounting arrangement and power or controller interface. A clear specification prevents the most common error in an inquiry—ordering a signal that looks right in a photograph but does not match the junction drawing.
Start with the operating purpose, not the housing photo
Before selecting a diameter or housing color, identify who must read the signal and what decision they need to make. A vehicle approach may need a three-section red, yellow and green ball signal. A protected turn may need an arrow indication. A pedestrian crossing normally needs a red standing person and a green walking person. Tunnel, lane-control and temporary applications can require different symbols, brightness or mounting arrangements.
The phase drawing is the best starting document. It should show each movement, the lane served by every signal head, the indication required at each position and any special device such as a countdown display, bicycle signal or audible pedestrian unit. When this information is supplied with an inquiry, a manufacturer can check the configuration instead of making assumptions.
Choose the signal diameter for the viewing environment
100 mm, 200 mm, 300 mm and 400 mm are common nominal diameters. Selection is not simply a matter of choosing the largest size. The controlling factors are approach speed, expected viewing distance, number of lanes, road lighting, mounting height and the local authority specification.
| Typical signal size | Common use | Specification question to confirm |
|---|---|---|
| 100 mm / 200 mm | Compact assemblies, supplementary signals or limited-distance applications | Is the sight distance and authority standard suitable for the smaller optical area? |
| 300 mm | General road intersections and pedestrian crossings | Will the approach speed, mounting location and background provide adequate conspicuity? |
| 400 mm | Longer approaches, wider roads, high-speed or high-visibility applications | Does the structure, pole arm and wind loading allow for the larger head? |
Project specifications and local standards always take priority. The table is a planning aid, not a replacement for an approved design.
Define the number of sections and indication in plain language
Use a separate line for every signal head in the schedule. State the diameter, number of sections, color and symbol order. For example: “400 mm, 3 sections, red ball / yellow ball / green straight arrow, vertical housing” is much clearer than “400 mm traffic light.” A pedestrian head should identify its red and green symbols. A lane-control head should identify whether it uses a red cross, green arrow or other approved symbol.
For vehicle signals, confirm whether the green indication is a ball or an arrow. A green arrow is not a decorative option; it communicates a movement condition that must match the signal phase plan. If a head combines balls and arrows, include a layout drawing or a simple sketch with the inquiry.
Housing, lens and mounting are part of the same decision
The optical configuration is only one part of the signal head. Confirm whether the housing is polycarbonate, aluminum or another approved material; whether visors are required; whether the lens is clear, tinted, cobweb or another approved type; and whether the unit is vertical, horizontal, side-mounted or suspended. Also state the pole diameter or mounting bracket interface. These details affect installation time, spare-part compatibility and the finished appearance of a junction.
A useful project schedule
For each signal head, list: location or signal-group number, diameter, number of sections, indication sequence, housing material, lens or visor requirement, mounting method, operating voltage and required quantity. Add the applicable standard, delivery destination and any packaging requirement. This schedule can be reviewed before production begins.
Confirm the electrical interface before production
Signal heads must match the controller output and site power arrangement. Confirm operating voltage, cable-entry method, connector or terminal requirement, earthing arrangement and any surge-protection or backup-power condition. If countdown units, pedestrian sounders or remote monitoring are included, show them in the I/O list rather than adding them after the main signal head is chosen.
Request a drawing and sample approval
For export projects, the final safeguard is a confirmed drawing. It should show the front indication layout, dimensions, mounting points, cable entry and label information. For a new configuration, sample photos or a physical sample can also prevent misunderstandings about color sequence, arrow direction or housing orientation before a full shipment is packed.
Prepare a clearer traffic signal inquiry
GAOQIAO supplies vehicle, pedestrian, solar and lane-control traffic signal solutions for project requirements. Share the junction drawing, head schedule, required quantity, destination and expected delivery date so the product configuration can be reviewed correctly.
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