The Controller is the signal's brain. It consists of a computer that controls the selection and timing of traffic movements in accordance with the varying demands of traffic as registered with the controller unit by detectors. A signal head can contain one or more signal faces. 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 circular red, yellow, and green sections and sometimes red, yellow and green turn arrow sections as well.
Detectors are devices for indicating the passage or presence of vehicles.
In Farmers Branch 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 the wire loop. The purpose of preemption is to clear tracks of traffic stopped on them by traffic signals, and to help prevent other traffic from entering the crossing once it is clear. Emergency Vehicle Preemption Emergency vehicle preemption is used for Farmers Branch Fire and emergency medical vehicles. The purpose is to obtain a green light for the emergency vehicle as soon as possible or to hold an existing green light.