Signal Heads, Supports, Poles, and Wiring/Cabling
Heads and placement
Vehicle signal faces use 8-inch or 12-inch lenses; 12-inch lenses are typical on new high-speed installations, and backplates with retroreflective borders improve visibility. Visors and louvers control sun phantom and visibility. Mounting height is measured to the bottom of the signal face: 15 feet minimum above the pavement, up to about 19 feet where extra clearance is needed. Lateral placement puts the face over or near the lane it controls, with primary and secondary faces for redundancy.
Supports and poles
Common supports are mast arm (strain pole), span wire, and post-mounted. Foundations rely on anchor bolts, leveling nuts, grout, and correct torque. Span wire needs proper tension, sag, and messenger support; guy wires stabilize, they do not carry signal load. Clearances to power lines follow the NESC.
Wiring and cabling
Conduit, pull boxes, and handholes must drain and stay accessible. Conductors are sized for current and voltage drop, using traffic signal cable with standardized color coding. Metallic poles and cabinets are grounded and bonded; surge arrestors protect exposed runs. In the cabinet, load switches and flashers map controller outputs to field circuits, and splices must be waterproof.
Traps
Mounting height is to the bottom of the head, not the top or the pole base. Backplates are not cosmetic on high-speed approaches. A guy wire is not a span wire. Color codes are not interchangeable between manufacturers.
Rule of thumb
Keep total voltage drop under about 5 percent, with roughly 3 percent on the branch circuit. If a distant head is dim, upsize the conductor before adding a second power supply.