Underwater California subway tunnel celebrates 50 years in service, once the longest in the world

At the time of its opening, the Transbay Tube was the longest immersed tube in the world.Photo byCorey AgopianonUnsplash

BART’s Transbay Tube celebrated its 50th anniversary on Monday, marking half a century since the vital transit link first began carrying passengers beneath the San Francisco Bay. The 3.6-mile tube, which connects Oakland and San Francisco, opened for service on September 16, 1974, and remains a critical part of the Bay Area's transportation network.

At the time of its opening, the Transbay Tube was the longest immersed tube in the world. Construction began in 1965, requiring the removal of over 5.7 million yards of mud from the Bay to make room for the 57 sections of the tube, each about 330 feet long. Fabricated at Bethlehem Shipyards in South San Francisco, the sections were floated, towed into place, and sunk 135 feet below the surface of the Bay. Notably, the tube withstood the 1989 Loma Prieta earthquake with minimal damage, solidifying its place as a resilient engineering feat. Today, it continues to carry thousands of passengers between the East Bay and San Francisco daily.