Controllers, Detection, Phasing, and Timing
Controllers and cabinets
NEMA TS-2 and ATC-type controllers (such as the 2070) run the intersection. The cabinet holds the controller, detector racks, load switches, flasher, power supply, and the conflict monitor or MMU. Modes include pre-timed, semi-actuated, fully actuated, and coordinated. Rings and barriers define which phases may run concurrently; overlaps map phases to outputs such as right-turn arrows.
Detection
Inductive loops, video, radar, magnetometers, push buttons, and preemption inputs all generate calls. Detector parameters include call, extend, delay, memory, passage or gap time, and maximum presence. Preemption from fire, rail, or transit overrides normal coordination; priority adjusts it.
Timing and coordination
Cycle length, split, offset, force-off, and permissive windows control a coordinated system. Recall (max, ped, soft) determines what happens with no detection. Pedestrian WALK has a minimum duration, and pedestrian clearance is based on crossing distance divided by walking speed, commonly 3.5 feet per second. Plans change by time of day.
Traps
Gap-out is not max-out. Detector delay is not detector extend. Offset is measured in seconds from the cycle reference point. Recall is not the same as actuation.
Worked example
A 60-foot crossing at 3.5 ft/s gives 17.1 seconds of pedestrian clearance, so program 18 seconds. With a 90-second cycle, a 55-second main split and a 20-second offset, main green begins 20 seconds after the system reference and must force off before the side street split begins.