Seikan Tunnel Opening Anniversary

What Is Seikan Tunnel Opening Anniversary?

Every March 13th marks the anniversary of the opening of the Seikan Tunnel (青函トンネル, Seikan Tonneru) on March 13, 1988. On that day, the JR Kaikyō Line (津軽海峡線) began service through the world's longest railway tunnel at the time — a 53.85-kilometer undersea link connecting Honshu (Japan's main island) and Hokkaido beneath the Tsugaru Strait. The tunnel was the culmination of approximately 40 years of planning and 24 years of construction, and is said to have involved a cumulative total of some 14 million worker-days of labor.

An Engineering Achievement Decades in the Making

The idea of connecting Honshu and Hokkaido by undersea tunnel arose after a tragic ferry disaster in 1954, when Typhoon Marie sank five Seikan ferries in the Tsugaru Strait, killing about 1,430 people in total (the Tōya Maru disaster). The disaster demonstrated the vulnerability of the ferry route and spurred serious planning for a permanent fixed link. Engineering surveys began in the late 1940s, construction commenced in 1971, and the project overcame seabed geology, high water pressure, and repeated flooding disasters to reach completion in 1988. Tragically, 34 workers lost their lives during construction; a memorial to them stands at Cape Tappi in Aomori.

Inside the Tunnel

The Seikan Tunnel runs 23.3 kilometers beneath the seabed — the longest undersea section of any rail tunnel in the world at the time of its opening (a record it held until the Channel Tunnel opened in 1994). Two undersea stations — Tappi-kaitei and Yoshioka-kaitei — were built as emergency refuges and also used for tours; they closed as stations in 2014 and remain as emergency points (Tappi and Yoshioka "teiten"). In 2016, the Hokkaido Shinkansen (bullet train) began service through the tunnel, fulfilling the original vision of high-speed rail connecting Japan's northernmost major island to the rest of the country.

The Tunnel's Role in Connecting Japan

Before the tunnel opened, travel between Honshu and Hokkaido required either a flight or a multi-hour ferry crossing — always dependent on weather conditions. The Seikan Tunnel provided a year-round, weather-independent land link, transforming logistics, commerce, and tourism between the two islands. Today, the Hokkaido Shinkansen carries passengers between Tokyo and Shin-Hakodate-Hokuto in about four hours — a journey that once took far longer.

Fun Facts About the Seikan Tunnel

• Water pressure: At its deepest point, the tunnel withstands water pressure equivalent to 24 atmospheres — roughly 240 meters of water above.
• Length record: The Seikan Tunnel held the record as the world's longest railway tunnel until the Gotthard Base Tunnel in Switzerland opened in 2016 at 57.09 km.
• Gentle gradient: The steepest gradient is only 12‰ (12 meters per kilometer) so heavy freight trains can run through — one reason the tunnel is so long.
• Always humid: Seepage water is constantly pumped out, and the humidity inside stays close to 100%, so trains and equipment need protection against salt damage.