Loop detectors operate on the principle of:

Loop detectors operate on the principle of inductance, which is the correct choice. These detectors typically consist of a loop of wire embedded in the pavement, and they function by detecting changes in the inductive field around the loop. When a vehicle enters the loop, it induces a change in the magnetic field, which causes variations in the inductance of the loop. This change is detected by the loop detector system and is used to signal the presence of a vehicle.

Inductance is key in this process because it involves the property of a conductor to oppose a change in electric current and is influenced by the proximity of ferromagnetic materials (like cars) that alter the inductive characteristics of the loop. The design and operation revolve around this principle to ensure effective vehicle detection, making inductance the fundamental operating principle behind loop detectors.

In contrast, capacitance, resistance, and voltage do not play the same role in the functioning of loop detectors. Capacitance may relate to certain types of sensors but is not the operating principle for loop detection. Similarly, while resistance is a property of electrical components, it does not directly influence the vehicle detection capability of a loop detector. Voltage is simply a measure of electric potential and, while important in electrical circuits,