Visitors traveling to Japan may notice something unusual at certain intersections: traffic lights that appear blue or turquoise instead of the familiar green. At first glance, it might seem like a different traffic system or a technical mistake, but the explanation is actually rooted in Japanese language and cultural history.

For centuries, the Japanese word ao was used to describe both blue and certain shades of green. Although the language eventually developed a separate word, midori, for green, the older expression remained part of everyday speech. Even today, some traditionally green objects are still described using the word ao.

When modern traffic lights were introduced in Japan, the signal allowing drivers to proceed was green, just like in most other countries. However, people continued referring to it as ao, following the traditional language. This created an interesting situation in which the official terminology and the visible color did not completely match.

In 1973, Japanese authorities addressed the issue by adopting a shade of green that was as close to blue as regulations allowed. This helped respect the traditional terminology while keeping traffic signals within internationally recognized standards. As a result, some Japanese traffic lights have a distinctive blue-green or turquoise appearance.

Despite their unusual color, these signals serve exactly the same purpose as green traffic lights elsewhere: they indicate that drivers may proceed when it is safe and the intersection is clear. What looks like a small difference to foreign visitors is actually a fascinating example of how language and cultural traditions can influence everyday life, even something as ordinary as a traffic light.