What is Loop Detector?

A loop detector is a wire loop buried in the road surface that detects a vehicle's presence by sensing the change in inductance as a metal mass passes over it. It is the most reliable and most widely-deployed vehicle-detection technology for parking gates, traffic signals, and toll plazas. In parking, loops are placed: in the approach to a gate (to trigger the read), in the gate itself (to keep the arm up while the vehicle passes), and at the exit (to confirm departure for occupancy counting). The data the loop produces is binary (vehicle present / absent), and modern controllers add presence-duration timing for occupancy calculations. Alternatives — ultrasonic sensors, magnetometers, cameras — exist for above-ground or no-trenching deployments but trade off reliability or cost. For a Smart Parking deployment the loop installation cost is one of the largest line items, which is why most refresh-existing-site projects keep the loops and replace only the controllers and the back-end platform.