With BART announcing plans to seismically strengthen its Transbay Tube, the blog takes a look back at how the thing got put in place 50 years ago.
The 3.6 mile, $180 million tunnel began construction in 1965. Instead of carving out a tunnel below the sea floor, the tunnel was built on land in 57 sections at the Bethlehem Steel shipyard at Pier 70 in San Francisco. On average, each segment was about 325-feet long and weighed 800 tons.
Each two-tunnel segment was then loaded onto a barge and dropped one by one to the sea floor into a shallow trench and connected. The tube was completed in 1969, then outfitted with rails and electricity and opened for use in September 1974.
The BART system opened in September 1972 in stages and didn't connect the East Bay and San Francisco until the tube was opened.
You can watch video here - starting at the 3-minute mark - on the construction of the tube.
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