Signal Display, Detection, and Wiring Standards
Display requirements
Inspect signal faces for the number, size, and type required by plans and MUTCD: vehicle heads, pedestrian heads, arrows, and accessible pedestrian signals. Verify lens color and condition, visor and backplate placement, and that no face is blocked by signs, poles, or vegetation. LED modules must match the specified voltage and appear uniform, without dark sections or flicker.
Detection and wiring
- Inductive loops: verify turns, slot depth, sealant, lead-in cable, and splice location; measure loop resistance and insulation resistance to ground.
- Video and radar: confirm zones cover the intended approach and do not false-call adjacent lanes.
- Pushbuttons: mounted within reach, correctly assigned, and audible and visible features working.
- Wiring: follow NEC and plan color codes; use listed connectors, strain relief, and waterproof splices; bond grounding and surge protection.
- Test point-to-point continuity, detection calls, and pedestrian timing before acceptance.
Worked example
A loop detector calls intermittently during rain. The card is swapped with no change, so the fault is field-side. A megger test shows low insulation resistance to ground at a handhole splice made with a wire nut and tape. Re-splice with a waterproof, listed connector, re-test insulation, and confirm stable calls. Replacing the card would have wasted time and left the moisture path.
Traps
Blaming the detector card before testing the loop; using unsealed splices in handholes; installing the wrong number of turns; mixing LED voltages; and ignoring a pedestrian pushbutton because the vehicle phase works.