Infrared passive counting system for vehicular traffic

Abstract

Vehicular traffic flow is controlled by the use of signal lights. The signal lights change according to a predetermined time sequence, which is estimated by considering traffic flow data. Traffic flow data consists of the rate of flow of vehicular traffic at a particular junction, at a particular time, on a particular day of the year and the width of the road apart from other parameters as considered important by Traffic Engineers. It would be desirable to have a demand controlled traffic signaling system which records the instantaneous traffic flow rate and determines the time sequence for the control system for the signal light although the predetermined times normally used are determined on the basis of demand but on statistical data rather than demand on the spot. The conventional methods of measuring traffic flow rate on the spot are by counting traffic. Methods of the counting vehicular traffic utilizes methods such as the change of magnetic field within a buried current carrying coil under the surface of the road and the break of a circuit which is normally closed by an infrared beam or a microwave beam, when a vehicle passes. Both these methods employ an active circuit whose condition changes when a vehicle passes. This paper presents a vehicular traffic counting system that was designed and implemented using a pyroelectric cell as the sensor. The system has the advantage of not needing an active emitter such as an infrared beam or microwave radiation. The pyroelectric cell responds to a change in the incident infrared radiation. Every hot body emits radiation and a moving vehicle is an efficient emitter of infrared radiation. The radiation emitted by the moving vehicle was allowed to fall on a pyroelectric detector, which was kept fixed by the side of the road. The rate of change of radiation incident on the cell generated a current through the cell, which was converted to a voltage. This detected signal was used to count moving vehicles and the count was displayed on a seven-segment LED display. The system is passive and is able to count moving traffic from a distance of about twenty meters.