The system includes a first detector (1) positioned above the traffic lane which detects the presence of vehicles. The variation in echo distance determines the time taken to pass the altimeter. The variation in distance is used to determine the height of the vehicle. A second detector is used with the first to obtain the speed of the vehicle by measuring the time interval between the two detectors. The length of the vehicle is determined by combining the speed of the vehicle and the time for the vehicle to pass the detector. The height and length information is used to determine the type of vehicle. The detectors can be mounted e.g. on a street light (2) to provide coverage beams for each lane. The source is provided with voltage from the light. The information is relayed to a base station. Laser, acoustic or radio signals can be used.
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