The Origin of Traffic Lights


Editor's Note: Reader Andrea recently asked if we could cover the history of traffic lights. Here's what we had in the archives. "“Jason

We're still stumped on that whole chicken vs. 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 so much 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 to keep people from constantly running into each other.

Control Tweaks
The concept of a box with bars 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 on the 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 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. These cities were also on the forefront of an effort to streamline traffic signal controls (and thus improve the flow of traffic in general) by wiring several different intersections back into a single control tower.

This article was written by Maggie Koerth-Baker and excerpted from the mental_floss book In the Beginning: The Origins of Everything. You can pick up a copy in our store.