On August 10th, 2019 we learned about

The story of color-coded traffic signals and apparent disregard of color-blind drivers

My kids and I were recently staring at a traffic light, although apparently we weren’t really seeing the same thing. As the “rational adult” in the car, I was only looking at the red light, silently cursing it for making us late to our destination. The kids in the backseat saw something else though, which was a traffic system that didn’t seem to make any sense to people with red-green colorblindness like deuteranopia. Since as much as 8 percent of men alone face some degree of difficulty discerning red from green, my 10-year-old didn’t understand how we ever adopted a traffic system that allowed for confusion between the crucial commands of stop and go.

The start of color-coded signals

While even the Ancient Romans had road signs, nobody had automated traffic control systems until William Robinson’s track circuit signals started directing trains in 1867. Moving semaphore flags and gas-lit lamps told trains when it was safe to stop and go, and was one of the first systems to adopt red and green as traffic signals. However, in this case, green meant “caution” and white meant go, which would have been a clearer signal to colorblind engineers but also came with a severe risk of failure. In 1914, a red lens fell off of a signal lamp, reversing the intended message to stop and leading to a collision. In response, green was promoted to “go” and yellow was selected as new, distinct hue to signal “caution.” The change was apparently carried over to roadways, which had been attempting to rein in carriage traffic in a similar fashion since 1868 (with decidedly mixed results).

The first red, yellow and green traffic signal went up over a road in Detroit, Michigan in 1920. That design wasn’t immediately adopted on a large scale though, as there were questions about if motorists would even obey a traffic signal that wasn’t backed up by a police officer to monitor drivers’ behavior. That concern was naturally at odds with the need to make these systems automatic for the sake of efficiency, and there seems to have been very little worry over the color scheme involved in the signals themselves. After all, red had been associated with blood and danger for ages, and it was easily visible through air and dust particles thanks to it’s relatively scatter-proof wavelength, so why change it? Green was better than white, so who would have a problem with that?

How detrimental is deuteranopia to driving?

The answer would of course be colorblind drivers, although once the design of traffic lights was sufficiently standardized, they never had too much of a problem. While the exact hue of a stop or go signal may not be distinct to these drivers, the order of the lights in a traffic light usually are, making “top means stop” and easy way to avoid a collision. Thanks to these alternative streams of information, color-blindness isn’t generally detrimental enough to require special accommodation, at least as far as the law is concerned. While it would likely be appreciated if traffic lights had other distinct characteristics, especially when they’re rearranged in multiple, vertical rows, there’s no specific requirement demanding that we take our traffic signals back to the drawing board.

Signalling with shapes

That’s not to say that some folks aren’t looking to improve on traffic lights’ design though— a number of updates have been proposed that would add visual cues to lights that don’t depend on color or position. For example, designers Ji-youn Kim, Soon-young Yang, and Hwan-ju Jeon have proposed that stop signals be housed in triangular frames, caution in circular frames and go in square frames. This light design hasn’t been implemented yet, but this concept may represent a first step to a more carefully considered traffic signal that is clear for every driver.

Source: The origin of the green, yellow, and red color scheme for traffic lights by Scott, Today I Found Out

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