What is a common use for loop detectors in signal systems?

Loop detectors are primarily utilized in traffic signal systems to detect the presence of vehicles. Situated in the pavement, these detectors consist of looped wires that create an electromagnetic field. When a metal object, such as a vehicle, passes over or stops on the loop, it disrupts this field, signaling to the traffic control system that a vehicle is present.

This detection capability is crucial for managing traffic flow and signal timings. It allows the signal system to respond appropriately to changes in vehicle presence, optimizing traffic signal phases to improve intersection efficiency and safety. By accurately detecting vehicles, loop detectors help reduce congestion and enhance the overall functioning of traffic management systems.

Measuring temperature, monitoring air quality, and calculating speed, while important functions in various contexts, do not relate to the primary purpose of loop detectors in signal systems. Their design and operation are specifically geared toward vehicle detection, making that the correct answer.