Traffic signals

TRAFFIC SIGNALS

A Traffic Signal or Road Signal is a traffic control device or sign, operated by electrical power. 

Uses. It is used to regulate the traffic. An indication of traffic signal directs the traffic to stop, to get ready and to proceed alternatively. Road signals are erected on the edges of roads or at the islands in road junctions. In multi-lane traffic roads, the signals are positioned at a height sufficiently above the passing vehicles so as to have good visibility from a long distance.

See Fig. 15(a). Green, Yellow and Red are the color signals used.

Green indicates, the permission to go. Yellow signifies 'to get ready to stop'. Red indicates a mandatory stop of vehicles.

These three signals are arranged vertically in the order shown. See Fig. 15(b).

Sometimes, two more signals for left and right turns are also provided.

Time Cycle: The number of seconds required for one complete sequence of signal indications, i.e., green-yellow-red is called a Time Cycle.

A Free-Left turn is signified by a continuous flickering of green on the left-side signal. At the ends of pedestrian crossing, green man signal indicates ‘go' and red indicates 'stop'.

In important locations, continuously flickering signals in red or yellow color will be provided. The flickering indicates “to proceed with utmost caution'.

1. CLASSIFICATION OF TRAFFIC SIGNALS

1. Fixed Time Signals: These signals are set to repeat regularly a cycle of green-yellow-red lights. These signals have a minimum delay for a group of vehicles travelling along a series of intersections with interconnected signals. Disadvantages: It may hold vehicles from one direction when there is no traffic in the other direction. It results in delay.

2. Traffic Actuated Signals: These signals recognize the demand of the flow of the traffic and distribute the Time Cycle accordingly.

Advantages: It reduces delay. It increases the capacity of flow of vehicles. It is adaptable to short-term fluctuation in traffic. It is effective at isolated intersections of roads.

Disadvantages: High initial and maintenance cost; requires sophisticated equipment.