How does a traffic counter or loop work?
The loops are 6 foot square coils of wire. A coil of wire has an electrical property called Inductance. The inductance of a loop of wire decreases when a conductive material is brought near it. This is the same principle used in a metal detector. Electronics, located in the roadside cabinet, measure changes in inductance of the loop. And, thus, it detects vehicles driving over the loop. The time that a vehicle spends over the loop is measured and used to determine the level of traffic congestion.
