What describes a traffic signal that initiates a change in operation when vehicles arrive at the intersection?

• A. Arterial Highway
• B. Actuated Signal
• C. Phase
• D. Occupancy

Answer: (B)

A signal that adjusts its timing based on vehicles arriving is an actuated signal. Detectors—such as inductive loops, video, or infrared sensors—watch each approach for vehicles. When a vehicle is detected, the controller can start a green for that movement or extend the current green so more cars can pass, reducing unnecessary waiting. This responsive behavior is what sets actuated signals apart from fixed-time signals, which run on a predetermined cycle regardless of actual traffic. There are variations: fully actuated systems use detectors on all approaches to trigger any phase changes based on demand, while semi-actuated systems have detectors only on minor approaches, with the major street often maintaining a fixed green. Occupancy refers to how long a detector is occupied by a vehicle, not the signaling action itself, and a phase is simply one part of the signal cycle for a specific movement.