We've been given the green light to tell you about the origin of traffic signals. Go ahead and cruise through the text, and we'll let you know when to stop.
SIGN O' THE TIMES
We're still stumped on that whole chicken versus egg question, but there's one thing we do know for sure -traffic congestion predates the automobile. Long before the invention of the internal combustion engine, horses and people were already having enough trouble yielding to each other at intersections that, in 1868, a British railroad engineer designed the first traffic signal to help them out. Oddly, the contraption only featured two settings: "stop" and "caution," indicated by a bar held horizontally or lowered to a 45-degree angle.
At night, red and green lights were used to make the bar visible, meaning that, in this case, "green" meant "slow down." A proclamation issued by London's police commissioner in 1868 explained the system as well as the then-novel concept of pedestrian right-of-way, and for the first time, cities had a way of keeping people from constantly running into each other.
CONTROL TWEAKS
The concept of a box with bar sticking out each side like arms was modeled on the naval semaphore system, a way of communicating between ships where a sailor would hold certain flags at certain angles to create messages. As overly complicated on the street as it was at sea, it soon fell out of favor, replaced by an electrical upgrade. The first light-based traffic signals were probably those installed in Salt Lake City, Utah, by police officer Lester Wire in 1912. Featuring a slanted roof to shed rain and snow, Wire's signal boxes contained dye-colored lights that shone through coverless circular openings and were powered by the same wires that ran electric trolleys. Like the earlier signals, Wire's lights only had two settings, in this case "stop" and "go," and were manually operated on-site by a police officer.
A similar system was installed (and patented) in Cleveland in 1914, but with a significant safety improvement. Unlike their western counterparts, the Cleveland lights were all connected back to the same control station and wired so that it was impossible to accidentally tell both directions to "go" at once (an important development, no doubt).
Amazingly, the first three-setting lights didn't come along until the 1920s. Based on railroad signs being used since 1899, the three-light signal first appeared in Detroit and New York City between 1920 and 1922. Not surprisingly, those heavily-trafficked cities were also on the forefront of an effort to streamline signal controls (and thus improve the flow of traffic in general) by wiring several different intersections back into a single control tower -innovations that were quickly mimicked the world over.
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The article above was reprinted with permission from mental_floss' book In the Beginning. From Big Hair to the Big Bang, here's a Mouthwatering Guide to the Origins of Everything by our friends at mental_floss. Did you know that paper clips started out as Nazi-fighting warriors? Or that cruise control was invented by a blind genius? Read it all in the book!