Traffic Signal Installation Day

What Is Traffic Signal Installation Day?

Every August 20th is "Traffic Signal Installation Day" (交通信号設置記念日, Kōtsū Shingō Setchi Kinenbi) in Japan. On August 20, 1931, three-color traffic signals — red, yellow, and green — were installed at 34 locations in Tokyo, including the Owarichō crossing in Ginza (today's Ginza 4-chōme crossing) and the Kyōbashi crossing. The spread of traffic signals marked a watershed in Japan's urban traffic management, bringing order to streets increasingly crowded with automobiles, bicycles, rickshaws, and pedestrians.

Traffic Control Before Signals

Before signals became common, traffic at major Tokyo intersections was controlled by police officers using hand signals and manually operated signboards. Japan's very first automatic traffic signal, an American-made unit, was installed at Tokyo's Hibiya intersection in March 1930, the year before the Ginza installations. The electric traffic signal was already in use in the United States from the 1910s and offered a scalable, consistent solution to growing traffic.

Why Japan Calls Green "Blue"

Japanese traffic lights are green, yet people call them "ao" (blue). Early regulations are said to have described the light as "green," but one theory holds that newspapers of the time wrote "blue signal" and the name spread, and the legal wording is said to have later become "blue" as well. Japan's first automatic signal, a U.S.-made unit installed at Tokyo's Hibiya crossing in March 1930, even had the words "Go," "Caution," and "Stop" written on its glass to explain the colors. Japanese traditionally uses "ao" for some green things too, such as fresh leaves (aoba). By law, horizontal signals show green, yellow, and red from left to right, which puts the all-important red light closer to the center of the road; in snowy regions and narrow spots, vertical signals are sometimes used because snow is less likely to pile up on them.

Road Safety and Traffic Engineering

Japan's traffic signal network is part of a broader traffic safety infrastructure that has achieved remarkable results. From a peak of 16,765 traffic fatalities in 1970, Japan reduced road deaths to 2,547 in 2025, through a combination of improved road engineering, vehicle safety standards such as mandatory seat belts, traffic signal optimization, and sustained public education campaigns. In cities, neighboring signals are coordinated so that vehicles can pass through several intersections with fewer stops.

Fun Facts

• Ginza 4-chōme: The Ginza 4-chōme crossing — one of the sites of the 1931 signal installation — remains one of Tokyo's busiest and most famous intersections.
• LED signals: Japan has been converting its traffic signals to energy-efficient LEDs, which last longer and are less prone to "phantom lighting" when the setting sun shines on them. Tokyo completed the switch for all its signals in fiscal 2021.