Transbay Tube
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The Transbay Tube is the part of BART which runs under the San Francisco Bay in California and is the longest underwater tube for rapid transit in the world. The tube itself is 3.6 miles (5.7 km) long; including approaches from the nearest stations (which are underground), it totals 6 miles (9 km). At a maximum depth of 135 feet (41 meters) below the surface, the Transbay Tube is the deepest vehicular tube in service today.
The tube was constructed on land, transported to the site then submerged and fastened to the bottom (mostly by packing the sides with sand and gravel). This is in contrast to tunneling, where earth is removed to leave a passage, the method of underground mines, and, for example, the Channel Tunnel between France and England.
Conception and construction
The idea of an underwater tube traversing the San Francisco Bay was originally conceived in October 1920 by Major General George Washington Goethals, the builder of the Panama Canal. The alignment of Goethal's proposed tube is almost exactly the same as BART's Transbay Tube. In 1947, a joint Army-Navy Commission recommended an underwater tube as a means of relieving automobile congestion on the then ten-year old San Francisco-Oakland Bay Bridge.Seismic studies commenced in 1959 and construction was started in 1965. The tube itself was finished in 1969. The tracks and electrification needed for the trains was finished in 1973 and it was opened to service in 1974. The tube is made of 57 individual sections that were built on land and towed out into the bay by a large barge. They were then positioned above where they were to sit and lowered into a trench packed with soft soil, mud and gravel for leveling along the bay's bottom. Once the sections were in place, bulkheads at each end of each of the sections were removed and a protective layer of sand and gravel was packed against the sides. It cost approximately $180 million in 1970.
The western terminus of the tube directly connects to the downtown Market Street Subway tunnel near the Ferry Building, north of the Bay Bridge. The tube crosses under the bridge between the San Francisco peninsula and Yerba Buena Island, and emerges in Oakland along 7th Street west of Interstate 880.
Incidents
In January 1979, an electrical fire occurred on a train as it was passing through the tube. One firefighter was killed in the effort to extinguish the blaze. Since then, safety regulations have been updated and current trains have less flammable material.As a precaution, the tube has been shut down along with the rest of the BART lines following significant earthquakes. The largest to date was the 1989 Loma Prieta earthquake, but the tube was found to be safe and reopened just six hours later. Many area highways were damaged, and the Bay Bridge was unusable, so BART ridership reached very high levels.
Trivia
The tube appears briefly at the end of George Lucas' film THX 1138. The final climb out to the daylight was actually filmed, with the camera rotated 90 degrees, in the incomplete (and decidedly horizontal) Transbay Tube before installation of the track supports, with the character using exposed reinforcing bars as a ladder.See also
External links
- [BART's Transbay Tube] - Detailed history of the tube and primary source of information for this article
- Note: The San Francisco-Oakland Bay Bridge crosses the Transbay Tube, so it is both upstream and downstream.
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