Wireless magnetic sensor networks offer an attractive, low-cost alternative to inductive
loops, video and radar for traffic surveillance on freeways, at intersections and in parking
lots. The network comprises 5” diameter sensor nodes (SN) glued on the pavement
where vehicles are to be detected. The SNs send their data via radio to the “access point”
(AP) on the side of the road. The AP forwards sensor data to the Traffic Management
Center via GPRS or to the roadside controller. Because such networks can be deployed in
a very short time, they can also be used (and reused) for temporary traffic measurement.
Vehicles are detected by measuring the change in the Earth’s magnetic field caused by
the presence of a vehicle near the sensor. Two sensor nodes placed a few feet apart can
estimate speed. A vehicle’s magnetic ‘signature’ can be processed for classification and
re-identification. The paper describes the algorithms and presents experimental results
comparing the accuracy of such a wireless sensor network with loop detectors and video.