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 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 Bakersfield these usually 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. Some intersections now use a video camera system for detection. This involves a fixed camera aimed at oncoming traffic. When a vehicle crosses or arrives at a pre-defined location in the field of view of the camera, the vehicle is detected.