Controlling traffic with radio

The author reviews the role of radio frequencies in the control of traffic and pedestrians. He discusses active control of traffic junctions based on vehicle actuated demands; implying a requirement for vehicles approaching junctions or waiting at junctions to be detected, and for that detection event to be notified to the junction controller. It is also desirable to know the direction of an approaching vehicle. The great advantage of this approach is that the junction control system can generate a sequence for the light signals which should optimise the prevailing traffic flow. Detectors use a wide range of frequencies within the electromagnetic spectrum, ranging from visible light range down to tens of kHz. Within the radio frequency range, and subject to the operating frequency used, traffic detection can be effected using either below ground or above-ground antennas. The author describes both of these systems and the frequencies used for the latter. The operation and implementation of these systems is then discussed