4.3.1 Inductive Loops (Practical System)
Loop detector technology has become the most widely used sensor in
incident detection systems. They are capable of measuring flow and
occupancy, and estimating vehicle speed. They can also be used to
actuate traffic control devices and detect congestion and incidents.
An inductive loop detector consists of one or more loops of wire
embedded in the pavement and connected to a control box, excited
by a signal ranging in frequency from 10 KHz to 200 KHz. When a
vehicle passes over or rests on the loop, the inductance of the loop is
reduced showing the presence of a vehicle.
The raw data supplied by inductive loop detectors are vehicle
passage, presence, count, and occupancy. For incident detection, loop
data is usually relayed to a controller for analysis.