Dynamic Road Traffic Signal Control System

The Need!

One of the major problems faced in any metro city is traffic congestion. Getting stranded in between heavy traffic is a headache for each and every person driving the vehicle and even to the traffic police in controlling the traffic.

One of the oldest ways of handling traffic was having a traffic policeman deployed at each junction and manually controls the inflow of traffic through hand signaling. However this was quite cumbersome and then came the need for a different type of control – using Traffic signals.

Traditional Traffic light controllers used a fixed predetermined schedule for traffic inflow for each direction in the junction. The controller was an electro mechanical controller which consists of mechanical systems operated electrically. It consists of three major parts- a dial timer, a solenoid and a cam assembly. A motor and a gear assembly operates the dial timer which in turn are responsible to energize or de energize a solenoid which in turn operates a cam assembly which are responsible to provide current to each signal indications. The dial timer is used to provide repetition of fixed duration intervals.

However the whole idea of a fixed time traffic light controller is not convenient for cities where traffic flow is variable. For this reason a dynamic traffic control system is needed, which controls the traffic signals according to the density of traffic.

How a Dynamic Traffic Control System looks like?

  • A Display: It is the basic traffic signal display which the vehicle driver or the commuter can see. It can be a conventional incandescent discharge lamps or an arrangement of LED.
A traffic Signal display
A Traffic Signal display
  • A Detector unit: It is the unit which detects the presence of vehicles and sends this information to the controller to be processed.

Practically there are two types of Detectors:

  • Inductive Loop Detector: It consists of a coil of wire embedded into a groove on the road surface which is sealed with a rubber.  It detects change in frequency. The inductor coil is connected with the detector which detects the change in resonant frequency of the coil loop and accordingly controls the triggering of the relay which is used to trigger the traffic signals. Basically it works on the principle that when a car moves over the inductor coil, the inductance of the coil decreases. This decreased inductance causes the resonant or oscillation frequency to increase and the electronics unit accordingly sends electric pulses to the control unit to control the switching of traffic lights. However a disadvantage of such system is the inductor loops are prone to electromagnetic interference, i.e. electromagnetic radiation from other devices can also affect the magnetic field and hence the inductance of the coil. They are also more prone to failure and require high installation cost and also cause disruption of traffic.
Traffic Signal Control using Inductive Loop Detector
Traffic Signal Control using Inductive Loop Detector
  • Sensors mounted on the Poles: It can be a simple IRLED-Photodiode arrangement or a video detection unit which can detect the presence of vehicles. This works on the principle that when a car passes between the IR transmitter and IR receiver, the IR light is blocked and as the result the resistance of the photodiode increases. This change in resistance can be converted to electrical pulses, used to control the traffic lights.
Traffic signal control using sensors mounted on poles
Traffic Signal Control using Sensors Mounted on Poles
  • A controller unit: It is the unit which receives the detector output which gives an indication of the presence of vehicles and thereby makes a calculation of the traffic density and accordingly controls the display unit. It can be a microprocessor based computer or a simple microcontroller.
A Control Unit
A Control Unit

A Simple Demonstration of Density Based Traffic Signal Control using IR Sensors

A prototype of traffic signal control system can be made using IR sensors along with Microcontroller and LEDs which can prove a worth for the real time application of controlling traffic signals based on the density of traffic. The junction considered here is a 4 side junction with traffic flow in each side in only one way. The system consists of the following three main components:

  • Display Unit: It consists of 3 LEDs- Green, Red and Amber in each side of the junction, with an all total of 12 LEDs.
  • Detector Unit: It consists of an arrangement of photodiode and IR LED combination at each junction which detects presence of vehicles by detecting change in resistance.
  • Controller Unit: It consists of a microcontroller which receives the IR sensor output and accordingly controls the glowing of LEDs
A prototype of Density based traffic signal control
A Prototype of Density based Traffic Signal Control
Block Diagram showing Density based Traffic Signal control
Block Diagram showing Density based Traffic Signal control

In normal conditions, i.e. when there is no vehicle on the road, the IR transmitter or the IR LED transmits IR light which is received by the photodiode, which starts conducting. As the photodiode conducts, the corresponding transistor also conducts giving an output of low logic signal to the microcontroller. The same principle works for all other IR sensor- transistor arrangement. The microcontroller makes each LED glow for a fixed amount of time.


Now if there is presence of vehicles, the communication between the IR transmitter and the receiver is interrupted, i.e. the photodiode receives less or no amount of light from the IR diode and accordingly the base current to the transistor reduces, eventually making the conductor go to off condition. This causes an output of high logic signal from the transistor, to the microcontroller.  The microcontroller accordingly changes the glow time of the green LED of the corresponding junction to a higher value.

Thus as number of vehicles increases, the green light glows for more time, allowing a quick flow of traffic from the junction side.

So by now, we had a brief idea about controlling traffic signals using different means. How about a control through the vehicle itself, like a communication between the vehicle and the traffic signals. This system is already being used in some parts of the world. Get to know about that and give your feedback.

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