Permanent Inductive Loops are considered the most reliable traffic detection method available. An inductive loop consists of coiled wire that is formed into a square, circle or rectangular loop. That loop is then installed into or under the surface of the roadway.

Inductive loops are used in signal detection and work like a metal detector. Once a vehicle drives over a loop sensor, the loop field changes which allows the device to detect the presence of an object (mainly a vehicle).

Inductive loops are referred to as presence detectors, and in traffic detection are often used in combination with axle sensors to collect classification data.