Why Does Japan Have Blue Traffic Lights Instead of Green?

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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