Traffic Surveillance with Wireless Magnetic Sensors

Abstract

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.