Answer: The Sides Indicate The Danger Level

There’s an entire invisible world right around us every day: a world of regulations and rules, standard sizes and color choices, and more, all designed to shape the world around us in an orderly and consistent way. Many of these things, like the stop sign, have been around for so long that we don’t even question why they are the way they are.

Some of the elements of the stop sign make sense. Red is eye catching and mirrors both the red of the stop light and the general caution that we attach to red things (other things, like warning labels, are often accented in red too). The bold and large letters also make sense—they’re easy to read. But why an octagon? The reason can be found way back in 1923. At that point in time, traffic signage was quite non-standard, but engineers at the Mississippi Valley Association of State Highway Departments wanted to change that.

Not only did they put out recommendations that proved highly influential and shaped how signage was codified across the country, but they had a rather analytical and focused method for determining how a sign should be shaped. Their logic was this: the number of sides a sign had should correspond to the danger/risk level the sign indicated. Plain rectangular and square signs were fine for information (like a speed limit posting), but stop signs should have 8 sides to indicate the increased risk of not stopping at an intersection. The signs for what they considered the most dangerous thing at the time, railway crossings, were round (because, technically, a circle has infinite sides).

While we appreciate what they were going for (and think it works well for the stop sign), the whole circle-as-infinitely-sided argument might look great on paper, but falls apart a wee bit in real life. Circles don’t seem very dangerous and if we had been in charge of the whole thing, we might have reserved a multi-pointed star as the sign for really dangerous areas since the spiky shape screams “pain to all those who disregard this sign”.