His proposal called for building on bay mud, which anticipated some of the seismic design aspects of the finished Transbay Tube, and was estimated to cost up to US$50,000,000 (equivalent to $854,100,000 in 2023).

[13][14] In 1947, a joint Army-Navy Commission recommended an underwater tube as a means of relieving automobile congestion on the then-ten-year-old Bay Bridge.

[16][17] Seismic studies commenced in 1959, including boring and testing programs in 1960 and 1964, and the installation of an earthquake recording system on the Bay floor.

The tube's route was modified after preliminary surveys were unable to identify a continuous bedrock profile, requiring more precise boring and probing of the Bay floor.

[24] The tracks and electrification needed for the trains were finished in 1973, and the tube was opened to service on September 16, 1974,[25] five years after the originally-projected completion date, after clearing California Public Utilities Commission concerns regarding the automated dispatch system.

[29] The structure is made of 57 individual sections that were built on land at the Bethlehem Steel shipyard on Pier 70[30][31] and towed out into the bay by a large catamaran barge.

[32] After the steel shell was completed, water-tight bulkheads were fitted and concrete was poured to form the 2.3-foot (0.70 m)-thick interior walls and track bed.

They were then floated into place (positioned above where they were to sit), and the barge was tethered to the Bay floor, acting as a temporary tension leg platform.

[37] The western terminus of the Tube directly connects to the downtown Market Street subway near the Ferry Building, north of the Bay Bridge.

The tube crosses under the western span of the Bay Bridge between the San Francisco Peninsula and Yerba Buena Island, and emerges in Oakland along 7th Street, west of Interstate 880.

Each tunnel has 56 doors opening into the lower gallery, spaced approximately 330 feet (100 m) apart, numbered consecutively from the San Francisco side of the tube.

[41] Each end of the tube is secured to the vent structures with a patented sliding seismic joint[43] which allows six degrees of freedom (translation along and rotation about three axes).

"[49] However, settling of the tube within its trench and the Loma Prieta quake had reduced the allowable movement of the seismic joints to as little as 1.5 inches (38 mm).

[44][50] The 1991 study was followed by a more detailed BART Seismic Vulnerability Study, published in 2002, which concluded the fill packed around the tube might be prone to soil liquefaction during an intense earthquake, which could allow the buoyant hollow tube to break loose from its anchorages or cause movement that would exceed the capacity of the sliding seismic joints.

[57] In order to complete this work during 2013, BART closed one of the two bores of the tube early midweek (Tuesdays, Wednesdays and Thursdays), resulting in delays of 15–20 minutes.

[61][62] One firefighter (Lt. William Elliott, 50, of the Oakland Fire Department) was killed[63] by smoke and toxic fume inhalation (generated from burning plastic materials) during the effort to extinguish the blaze.

363 had made an emergency stop in the Transbay Tube while traveling towards San Francisco at approximately 4:30 p.m., reporting smoke and a possible fire.

[41]: 17–18  Central operations shut down power to the third rail, but restored it 40 seconds later in an effort to uncouple the lead portion of the train from the burning cars.

By the time they reached the area of door #51, their portable air masks were starting to run low, and Lt. William Elliott began to have trouble, requiring assistance from his fellow firefighters.

377 was dispatched from West Oakland in "road manual" to rescue the firefighters; the train operator moved with passengers on board because she assumed the cause of the delay had been resolved.

Critically, nine minutes elapsed between the time that power was restored and when the line supervisor informed BART central they were unable to uncouple the cars, which allowed the fire to grow.

111 with over 1,000 passengers onboard could have resulted in an even larger disaster if the control cables had failed in the eastbound tunnel due to the spread of the fire.

[78] According to a 2010 survey by the San Francisco Chronicle, the Transbay Tube is the noisiest part of the BART system, with sound pressure levels inside the train reaching 100 decibels (comparable to a jackhammer).

[79] In 2015, after replacing 6,500 feet (2,000 m) and grinding down (smoothing) 3 miles (4.8 km) of rail in the tube, BART reported a reduction of noise and positive feedback from riders.

[80] Ship traffic passing through the Bay can damage the anodes used in the Tube's cathodic protection system when dropping anchor.

Trains were delayed by 15 to 20 minutes, with normal service resuming around 1 p.m.[40] In April 2017, the derrick barge Vengeance, which was working for BART performing Tube anode maintenance, capsized and sank at night during a late winter storm.

The proposed four-bore tunnel would emerge at the Salesforce Transit Center to provide connecting service to Caltrain and the planned California High-Speed Rail (CHSR) system.

In 2018, BART and CCJPA, the agency responsible for Capitol Corridor commuter rail service, began planning to conduct a feasibility study to narrow the possible alignment options for the proposed second crossing.

[85][86] The study would continue to consider standard-gauge railway options in order to allow connections to Caltrain, CHSR, Capitol Corridor, and potentially other rail services.

[93] One of the early sections of the video game Dead Space features a sound sample taken from a ride through the Transbay Tube.