Classification of Traffic Signals

Traffic signals are the control devices which alternately direct the traffic to stop and proceed at intersections using red and green traffic light signal automatically.

The signals are classified into the following types:

• Traffic Control Signals
• Fixed time signals
• Manually operated signals
• Traffic actuated (automatic) signals
• Pedestrian signals
• Special traffic signals

1.Traffic Control Signals

These are provided with three colored light glows facing each direction of traffic flow.

Red light indicates STOP

Yellow amber light indicates the clearance time for the vehicles which have entered the intersection area by the end of green signal

Green light indicates GO

A typical traffic signal showing the arrangement of three light glows is shown in this fig.

Traffic control signal are further classified into the following 3 types.

a.Fixed Time Signals

These signals are set to repeat regularly a cycle of red, amber yellow and green lights. Depending upon the traffic intensities, the timings of each phase of the cycle is predetermined. Fixed time signals are the simplest type of automatic traffic signals which are electrically operated.

Draw backs of the signals: The cycle of red, yellow and green goes on irrespective whether on any road, there is any traffic or not. Traffic in the heavy stream has to stop at end phase.

b.Traffic Actuated Signals

In these signals the timings of the phase and cycle are changed according to traffic demand.

In semi-actuated signals, the normal green phase of a traffic stream may be extended upto a certain period of time for allowing the vehicles to clear off the intersection.

In fully-actuated signals, computers assign the right of way for the traffic movement on turn basis of traffic flow demand.

c.Manually Operated Signals

In these types of signals, the traffic police watches the traffic demand from a suitable point during the peak hours at the intersection and varies the timings of these phases and cycle accordingly.

2.Pedestrian Signals

When the vehicular traffic remains stopped by red or stop signal on the traffic signals of the road intersection, these signals give the right of way of pedestrians to cross a road during the walk period.

3.Special Signals or Flashing Beacons

These signals are used to warn the traffic.

When there is a red flashing signal, the drivers of vehicles must stop before entering the nearest cross walk at the intersection or at a stop line where marked.

Flashing of yellow signals are used to direct the drivers of the vehicular traffic to proceed with caution.