Who invented the traffic light, and why specifically red-yellow-green?
Colors have been used to direct traffic for almost 200 years. How is the development of traffic lights related to a gas explosion and complaints of racism?
Regulating traffic using colors is not a new idea; it has been with us on roads all over the world for almost 200 years. How was it born, and who decided on the colors and their meanings?
Red, green… explosion!
The idea of using colors to regulate traffic was not born for cars, because at the beginning of the 19th century there were none (Karl Benz registered the patent for the first modern car in 1886). It came from the world of railways, where around 1840 a signaling system using semaphore flags was developed, the first of which was installed in London around 1842 by Charles Hutton Gregory, and later the use of colored lanterns was also introduced.
About half a century later, British railway engineer John Peake Knight proposed using colored lanterns to regulate other types of traffic and installed a traffic light for carriages and pedestrians near Westminster Bridge in London, so that lords on their way to vote in parliament could cross the street safely. Semaphore arms were used by day, and red and green gas lanterns by night, with a policeman manually operating the switches that controlled which color was displayed to carriages and which to pedestrians. This was the world's first traffic light, but it did not last long — just about three weeks after installation, a gas leak from one of the lanterns caused the traffic light to explode and injured the policeman who was operating it.
From gas to electricity
In the decades after the first traffic light, similar designs based on various types of fuel lamps spread throughout the world. In the USA, a design appeared with the words "Go" and "Stop" next to colored lenses that were illuminated by kerosene lamps, and the policeman who operated the device blew a whistle before every change.
In 1912, Lester Farnsworth Wire, a policeman from Salt Lake City, Utah, developed the first electric traffic light, which looked like a birdhouse on a pole, with red and green lights that were operated manually. The traffic light was installed in Cleveland, Ohio, with additions by planner James Hoge, including a buzzer that warned before switching between colors and a mechanism for manual control in emergencies by the police.
Another color for the collection
The problem with a red-green traffic light is that it did not allow for preparation or coordination between manual traffic lights for several directions at the same intersection. The solution came in 1920 from William Potts, who was in charge of traffic signaling for the Detroit Police Department. Potts added a third light, amber-orange, to serve as a transition between green and red and allow traffic lights facing all four directions at the intersection where it was installed, which handled 20,000 cars a day, to operate simultaneously.
Traffic lights against racism?
Despite all the names we mentioned earlier, many in the world attribute the invention of the traffic light to Garrett Morgan, a black entrepreneur and printer from Cleveland. Morgan, who called himself the "Black Edison," received a patent approval in 1923 for a three-position traffic light. As mentioned, he was not the first to invent a traffic light, and not even the first to add an intermediate state — but he was the one who managed to register the rights to the mechanism. He was drawn into the subject after seeing an accident at an intersection in Cleveland, and according to stories, it followed claims by the black community that white police officers operating manual traffic lights were discriminating against them. General Electric bought the patent from him for $40,000, an amount equivalent to about $780,000 today.
Why specifically red, yellow, and green?
The short answer: because the railway companies had already done their homework. Red was chosen to symbolize a stop because it has the longest wavelength of the visible colors, which makes it visible from the greatest distances, even in fog or rain. It also has a biological connotation of danger — red is associated with blood and fire, and therefore "jumps" into consciousness immediately.
Green was actually not the first choice of the railways for "go." In the earliest versions of railway signaling, white meant "go" and green meant "caution." This turned out to be a bad idea: white lights could look like stars or streetlights from a distance, and at least one case of a train accident was attributed to this confusion. A green light, on the other hand, is not common and therefore it is impossible to be mistaken about it.
Yellow, as we remember, was added last — and that was exactly Potts' contribution in 1920: not a new color, but the idea of using it as a transition signal between green and red, to give drivers reaction time.
Additional facts about traffic lights
In Japan, the "green" traffic light is defined as "blue" (aoi), a remnant of an old cultural-linguistic struggle over the distinction between green and blue in Japanese.
The green light in many modern traffic lights is not pure green, but contains a bluish tint, to make it easier for people with color blindness to distinguish it from red (red-green color blindness is the most common type of color blindness).
