Traffic Lights – How they Work, Programs, Sensors

Traffic lights are signaling devices installed at pedestrian crossings, road intersections or at any other points where the flow of traffic has to be regulated. Generally, a light stick has three parts – red on top, amber and green at the bottom. The red is for stop, the amber for caution and the green for go.
A traffic light stick often has two lights mounted vertically and are seen at exit to fire stations or railway crossings when traffic has to be temporarily stopped without any fixed time duration. These flash white or amber when cross traffic is not expected and red when traffic has to be stopped for example to let a fire truck drive out of the station.

There is another type of traffic light stick which is not installed at traffic intersections but handheld by police or other emergency agencies to control traffic. These are safety batons. The top half is encased in a transparent polycarbonate casing with an LED light in them. Such sticks are especially useful in a scene of an accident or in dark areas where traffic flow has to be monitored. Available in red and green color, the better models also have a flashing mode.

Programs and sensors in the control unit of traffic lights ensure that traffic and pedestrians move as smoothly and safely as possible. These control systems are run on programs that might simply be a clockwork mechanism or a highly sophisticated control and coordination system. In the United States of America, these controllers are standardized by the NEMA which sets benchmarks for connectors, operating limits, and intervals.