The controller is the signal's brain. It consists of electrical or computer controls that operate the selection and timing of traffic movements in accordance with the varying demands of traffic as registered with the controller unit by detectors. Signal faces are part of a signal head provided for controlling traffic in a single direction and consisting of one or more signal sections. These usually include solid red, yellow, and green lights and sometimes include red, yellow and green turn arrow lights as well. The signal head can contain one or more signal faces.
Detectors are devices for indicating the passage or presence of vehicles.
In Irvine, these consist of wire loops placed in the pavement at intersections. They are activated by the change of electrical inductance caused by a vehicle passing over or standing over the wire loop. According to the California Vehicle Code, when a red lens is illuminated with rapid intermittent red flashes, a driver shall stop before entering the crosswalk on the near side of the intersection. The driver may proceed, subject to the rules applicable to making a stop at a 4-way stop controlled intersection. When a yellow lens is illuminated with rapid intermittent yellow flashes, a driver may proceed with caution through the intersection or past the signal.