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Origin Story: The History, Evolution and Meaning of Colored Traffic Lights

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Origin Story: The History, Evolution and Meaning of Colored Traffic Lights

Traffic lights are something you see every day, but may not think much about them. In today’s society, traffic lights have become so normal that we might forget that once upon a time they did not exist. Let us look back at the long history of the traffic light and how it evolved to become the complex system we have today.

A traffic signal, or stoplight as it is also known, controls the flow of vehicle traffic through two or more intersections by giving drivers visual cues when to proceed, slow down, and stop. These signals may operate manually or by a simple timer which allows traffic to flow on one roadway for a set period, and then on the other roadway for another set period before repeating the cycle. In other cases, sophisticated electronic controllers continually adjust their operation in response to the time of day and the flow of traffic run signals. Engineers use traffic signals to avoid traffic congestion and improve pedestrian and motorist safety.

History of Traffic Lights


In the 1860s, London was the first to introduce traffic lights into the city. John Peak Knight, a railway manager, adopted the system from railroad signals in 1868. The railroads used red stoplights at night and green stoplights during the day to signal stops. In December 1868, Knight installed a similar system near London’s Westminster Bridge.



Electric traffic signals were first installed in Cleveland, Ohio, in 1914. This system had a green and red light with a warning buzzer that would sound when the light changed. In 1918, the first signal using the familiar green, yellow, and red lights was installed in New York City.



Semaphore arms were used during the daytime to stop traffic in both directions. On evenings, however, police officers manually flashed red or green lights to alert carriages. Knight chose red for the stop signal because it represented danger, while green was chosen because of its reassuring qualities.



However, as gas-powered lights are volatile, these early traffic signals caused serious injuries and accidents when they caught fire or exploded. Within a short time, Knight’s design was declared a public health hazard and banned from city streets.



Evolution of Traffic Lights

  • A Detroit police officer named William Potts invented the first four-way and three-way coloured traffic signals in 1920. It was the first time that red, green, and amber/yellow were used together. Several improvements were made to Potts’ design by Garrett Morgan and patented in 1923.
  • Despite advances in traffic signal technology, today’s traffic lights still use the same t-shaped design with three colours devised by Potts and Morgan. However, even today, people have been looking for ways to improve them, as well as the system that supports them, since the ’20s.
  • When traffic lights were first invented, each light was changed at certain, regular intervals. Over time, this caused congestion in some areas. Adler invented a system that detected the sound of vehicles honking and altered the lights when needed.
  • During the ’60s, the dawn of brilliant innovation led to the computerization of traffic signal systems. Computer software allows traffic lights to monitor traffic patterns and change automatically, based on traffic data. Modern traffic lights can monitor traffic, time, location, weather, and emergencies to adjust their lights accordingly.

What Do The Colours In A Traffic Signal Mean?


Red Traffic Light


Red lights are relative stop signals. Whenever the red light is on, all traffic should stop. Right-turning vehicles can pass through the intersection, but they cannot hinder the passage of passing vehicles and pedestrians. At red lights, vehicles cannot stop outside the parking area. Drivers are not allowed to leave their vehicles.



Green Traffic Light


As the signal light turns green, you are ready to move, but take care when you begin moving. Keep an eye on traffic from other directions. In case you want to turn left or right, you must check whether the signal permits it separately. If yes, turn while yielding to pedestrians and drivers heading in the opposite direction.



Yellow Traffic Light


A yellow light indicates to clear the road as soon as the signal turns from green to red. It denotes both prohibition and permission. During the yellow light, vehicles can continue to pass while crossing the stop line. It is best for pedestrians at the crosswalk to move on, remain in place, or return to their original position.



Traffic Signal Precautions

  1. At a zebra crossing, pedestrians always have the right of way. Let them cross first.
  2. No matter if you are driving or stopping, your seatbelt should always be on.
  3. If you intend to go straight, do not swerve right or left, otherwise, you might block someone wanting to go in that direction.
  4. Honking is annoying, and it causes noise pollution, which isn’t good for anyone.
  5. Being aware of vehicles passing by before you move is a good driving habit.

Also published on Medium.

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