The trafFc control system of the MetropolitanExpressway is collecting and processing traffic data obtained from vehicle detection sensors installed along the highway. This traffic data is then offered to the users of the highway as information on required travel time, congestion and the like.Most of the sensors installed along the Metropolitan Expressway are ultrasonic sensors. However, there have been several problems associated with previous types of ultrasonic vehicle detection sensors: 1.) in tunnels and on three lane sections of the highways, previous types of sensors detected vehicles erroneously due to the reception of unnecessary reflected signals which caused a decrease in the accuracy of detection, 2.) due to the fact that there are more than about 2,000 sensors installed, and 3.) speed measurement.This report is an outline of the intelligent vehicle detection sensors (hereafrer, I Type vehicle detection sensors) introduced to solve these issues.

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