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.
