A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Who decided red means "stop" and green means "go"?

March 7, 1986

Dear Cecil:

Who decided, back in the mists of time, that red was the color for "stop" and green the color for "go"? The commonest form of color blindness makes the colors totally useless. A warning sign that is near-invisible to a significant portion of the population strikes me as a bad idea.

Cecil replies:

Well, now's a fine time to mention it, Barb. Why didn't you bring this up 80 years ago?

The present system of color coding was developed by the railroads around the time of World War I. But its roots go back much further. Tradition among railroaders has it that red was chosen for "stop" in commemoration of a farmer who tried to flag down an early choo-choo with his red shirt. This is cute, but BS. Red, the color of blood, has been a danger signal since time immemorial. It's said the Roman legions bore the red banner of the war god Mars into battle 2,000 years ago.

The other colors have changed over time. When the first primitive railroad signaling devices were developed in the 1830s and 1840s, red meant "stop," green meant "caution," and clear (i.e., white) meant "go." This system had several defects. One obvious problem was the fact that the white signal could easily be confused with an ordinary white light. What was worse, however, was the fact that the system wasn't fail-safe. This was tragically demonstrated sometime around 1914. The red lens supposedly fell out of a signal so that it erroneously showed a white indication. This caused a train to sail through the "stop" signal, resulting in a disastrous crash. The railroads subsequently decided to drop white and make green "go" and yellow "caution." Yellow presumably was chosen because it was readily visible and offered the most striking contrast to the other two colors. When the first electric traffic signals were installed in Cleveland, Ohio, in 1914, they used red and green indications. When the first modern automatic traffic signals were put up in Detroit in the early 1920s, they used red, yellow, and green, and that's what we're stuck with today.

Colorblindness poses less of problem for drivers than you might think. About 8 percent of the population suffers from some color vision deficiency, with difficulty in distinguishing green and red being most common. But it's rare to find someone so colorblind they can't tell bright red and bright green apart. Usually they only have trouble with pastels or in dim light. If all else fails they can fall back on the knowledge that on most stoplights red is on top. Cecil speaks from personal experience. You'd never want to take me hunting for wild raspberries in the forest. But I can tell when the damn traffic lights say stop.

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