Why does Japan have a blue traffic light?

This is what happens when you have one word for two colors.

That’s when you see things like this. Drive around Japan long enough and you’ll probably run into one of the country’s mythical blue traffic lights. Elsewhere around the island you’ll find “go” signals that are decidedly teal, turquoise, and aqua. “Is this signal broken?” you might wonder. “Did some overworked light-monger install the wrong bulbs?” The answer, as Atlas Obscura points out, is not in the wiring: it’s in the Japanese language.

Hundreds of years ago, the Japanese language included words for only four basic colors: black, white, red, and blue. If you wanted to describe something green, you’d use the word for blue—“ao”—and that system worked well enough until roughly the end of the first millennium, when the word “midori” (originally meaning “sprout”) began showing up in writing to describe what we know as green. Even then, midori was considered a shade of ao. As you can imagine, this sudden switch-over had lasting effects in Japan.

Today you’ll still see green things dubiously labeled blue. A fruit vendor might sell you an ao-ringo (blue apple) only to disappoint you that it’s actually green. Likewise, green bamboos are called aodake (“blue bamboos”) and an inexperienced employee who could be described as “green” in America may be called aonisai, meaning a “blue two-year-old.” And that brings us to traffic lights.

Initially, Japan’s traffic lights were green as green can be. Despite this, the country’s official traffic documents still referred to green traffic lights as ao rather than midori. While international traffic law decrees all “go” signals must be represented by green lights, Japanese linguists objected to their government’s decision to continue using the word ao to describe what was clearly midori. The government decided to compromise. “In 1973, the government mandated through a cabinet order that traffic lights use the bluest shade of green possible—still technically green, but noticeably blue enough to justifiably continue using the ao nomenclature,” Allan Richarz writes for Atlas Obscura.

So, while it may appear that Japan uses blue traffic lights, the government assures us it’s actually just a very blue shade of green—green enough to satisfy international regulations, blue enough to still be called ao. Don’t ever say bureaucracy never solved anything. (And make sure you brush up on these driving etiquette rules while you’re at it.)

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In Japan, a game of Red Light, Green Light might be more like Red Light, Blue Light. Because of a linguistic quirk of Japanese, some of the country’s street lights feature "go" signals that are distinctly more blue than green, as Atlas Obscura alerts us, making the country an outlier in international road design.

Different languages refer to colors very differently. For instance, some languages, like Russian and Japanese, have different words for light blue and dark blue, treating them as two distinct colors. And some languages lump colors English speakers see as distinct together under the same umbrella, using the same word for green and blue, for instance. Again, Japanese is one of those languages. While there are now separate terms for blue and green, in Old Japanese, the word ao was used for both colors—what English-speaking scholars label grue.

In modern Japanese, ao refers to blue, while the word midori means green, but you can see the overlap culturally, including at traffic intersections. Officially, the “go” color in traffic lights is called ao, even though traffic lights used to be a regular green, Reader’s Digest says. This posed a linguistic conundrum: How can bureaucrats call the lights ao in official literature if they're really midori?

Since it was written in 1968, dozens of countries around the world have signed the Vienna Convention on Road Signs and Signals, an international treaty aimed at standardizing traffic signals. Japan hasn’t signed (neither has the U.S.), but the country has nevertheless moved toward more internationalized signals.

They ended up splitting the difference between international law and linguists' outcry. Since 1973, the Japanese government has decreed that traffic lights should be green—but that they be the bluest shade of green. They can still qualify as ao, but they're also green enough to mean go to foreigners. But, as Atlas Obscura points out, when drivers take their licensing test, they have to go through a vision test that includes the ability to distinguish between red, yellow, and blue—not green.

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