View into the Transbay Tube
|Location||San Francisco Bay, California, US|
|System||Bay Area Rapid Transit|
|Start||Embarcadero Station, San Francisco|
|End||West Oakland Station, Oakland|
|No. of stations||None|
|Opened||16 September 1974|
|Owner||San Francisco Bay Area Rapid Transit District|
|Operator||San Francisco Bay Area Rapid Transit District|
|Line length||3.6 mi (5.8 km)|
|No. of tracks||2|
|Track gauge||5 ft 6 in (1,676 mm)
|Electrified||Third rail, 1000 V DC|
|Highest elevation||Sea level|
|Lowest elevation||135 ft (41 m) below sea level|
The Transbay Tube is an underwater rail tunnel which carries Bay Area Rapid Transit's four transbay lines under San Francisco Bay between the cities of San Francisco and Oakland in California. The tube is 3.6 miles (5.8 km) long; including the approaches from the nearest stations (one of which is underground), it totals 6 miles (10 km) in length. It has a maximum depth of 135 feet (41 m) below sea level.
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 immersed tube technique is in contrast to bored tunneling, where rock is removed to leave a passage.
The Tube was the final segment to open in the original BART plan. All BART lines except the Richmond–Fremont line operate through the Transbay Tube, making it one of the busiest sections of the system in terms of passenger and train traffic. During peak commute times, over 28,000 passengers per hour travel through the tunnel with headways as low as 2.5 minutes. BART trains reach their highest speeds in the Tube, almost 80 miles per hour (36 km/ks), more than double the average 36 miles per hour (16 km/ks) speed in the remainder of the system.
Conception and construction
The idea of an underwater rail tunnel traversing San Francisco Bay was suggested by the San Francisco eccentric, Emperor Norton, in two proclamations that he issued in 1872. Official consideration to the idea was first given in October 1920 by Major General George Washington Goethals, the builder of the Panama Canal. The alignment of Goethals's proposed tube is almost exactly the same as today'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 Bay Bridge.
Seismic studies commenced in 1959, construction was started in 1965, and the tube was completed in 1969 after the final section was lowered on April 3, 1969. BART sold commemorative bronzed aluminum coins to mark the sinking of the final section. Prior to being fitted out, the Tube was opened for visitors to walk through a small portion on November 9, 1969. The tracks and electrification needed for the trains were finished in 1973, and the tube was opened to service on September 16, 1974, five years after the originally-projected completion date, after clearing California Public Utilities Commission concerns regarding the automated dispatch system. The first test run was performed by a train under automatic control on August 10, 1973. Train No. 222 ran from West Oakland to Montgomery Street in seven minutes at 68 to 70 miles per hour (30 to 31 km/ks) and returned in six minutes at the full speed of 80 miles per hour (36 km/ks), carrying approximately 100 passengers including BART officials, dignitaries and reporters.
The tunnel is set in a trench 60 feet (18 m) wide with a gravel foundation 2 feet (0.61 m) deep. Lasers were used to guide the dredging of the trench and the laying of the gravel foundation, maintaining route accuracy of within 3 inches (76 mm) for the trench and 1.8 inches (46 mm) for the foundation. Construction of the trench required dredging 5,600,000 cubic yards (4,300,000 m3) of material from the Bay.
The structure is made of 57 individual sections that were built on land at the Bethlehem Steel shipyard on Pier 70 and towed out into the bay by a large catamaran barge. 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. The section was ballasted with 500 short tons (450 t) of gravel before being lowered into a trench packed with soft soil, mud, and gravel for leveling along the Bay's bottom. Once the section was in place, divers connected the section with the remainder of the sections, the bulkheads between placed sections were removed and a protective layer of sand and gravel was packed against the sides. Cathodic protection was provided to resist corrosive action from the Bay's salt water.
Each of the 57 sections ranges from 273 to 336 feet (83 to 102 m) long. Each section is an average of 328 feet (100 m) long, measured along the tunnels' bore, 48 feet (15 m) wide, 24 feet (7.3 m) high, and weighs approximately 10,000 short tons (9,100 t). To conform with the route, 15 tube sections were curved horizontally, 4 were curved vertically, and 2 had horizontal and vertical curves, with the remaining 36 sections straight. Each section of the Tube cost approximately US$1,500,000 (equivalent to $9,680,000 in 2015), based on the US$90,000,000 (equivalent to $580,750,000 in 2015) construction contract.
The project cost approximately $180 million in 1970 (equivalent to $1.91 billion in 2015), with $90 million of that cost being spent on construction, the remainder going towards laying rails, electrification, ventilation and train control systems.
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.
The tube consists of two tunnels and a central maintenance/pedestrian gallery. Each tunnel has a bore approximately 17 feet (5.2 m) in diameter, with the track centerline offset 8 inches (200 mm) towards the outside from the bore centerline. The tunnels flank a gallery which contains maintenance and control equipment in the upper gallery, including a pressurized water line for firefighting. 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. The doors are locked from the gallery side and can be opened inwards (toward the gallery) from the tunnel through emergency hardware. Between doors, the tunnel has narrow 2.5-foot (0.76 m) wide walkways adjacent to the gallery space.
The upper section of the gallery space is also used as a duct, moving 300,000 cubic feet per minute (8,500 m3/min) of air under forced circulation. The tunnels are vented to the atmosphere at the San Francisco and Oakland ends and are vented to each other (through the upper gallery) with remotely-operated dampers 6 feet (1.8 m) long by 3 feet (0.91 m) high over every third door.
Each end of the tube is secured to the vent structures with a patented sliding joint which allows six degrees of freedom (translation along and rotation about three axes). As-designed, the joints allow movement of up to 4.25 inches (108 mm) along the tube's axis and up to 6.75 inches (171 mm) vertically or laterally.
The 3.6-mile (5.8 km) Transbay Tube has required earthquake retrofitting, both on its exterior and interior. Research done years after construction showed that 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. Retrofitting work required the fill to be compacted, to make it denser and less prone to liquefaction. On the interior of the tube, BART began a major retrofitting initiative in March 2013, which involved installing heavy steel plates at various locations inside the tube that most needed strengthening, to protect them from sideways movement in an earthquake. In order to complete this work during 2013, BART closed one of the two bores of the tube early on weeknights. The work, estimated to last approximately 14 months, was completed after only 8 months of construction.
Incidents and issues
January 1979 fire
On January 17, 1979 at approximately 6 p.m., an electrical fire broke out on a San Francisco-bound seven-car train (Train No. 117) as it was passing through the tube. One firefighter (Lt. William Elliott, 50, of the Oakland Fire Department) was killed by smoke and toxic fume inhalation (generated from burning plastic materials) during the effort to extinguish the blaze. The forty passengers and two BART employees aboard the stricken train were rescued by another train passing in the opposite direction. The poor communication and coordination observed during the January 1979 fire played a key role in developing National Fire Protection Association transit industry guidelines (NFPA 130, Standard for Fixed Guideway Transit and Passenger Rail Systems).
The cause of the fire was traced to a short circuit on Train No. 117. The collector shoe assemblies on the number five and six cars broke after striking a line switchbox cover which had fallen off a prior train (Train No. 363), resulting in a short circuit and fire.
Earlier that day, San Francisco-bound ten-car Train No. 363 had made an emergency stop in the Transbay Tube at approximately 4:30 p.m., reporting smoke and a possible fire. Troubleshooting without an external inspection revealed No. 363 had broken derail bars on the number six and eight cars, and an engaged parking brake on the number nine car. After clearing the derail bar circuits and manually releasing the parking brake, No. 363 was cleared to proceed, and upon reaching the end of the line in Daly City, was taken out of service for inspection.
The train following No. 363 was dispatched to run in "road manual" mode, where the train is operated by the onboard engineer, rather than by the computerized central control system. That train reported seeing derail bar debris between the tracks near where No. 363 had stopped, but the tracks remained clear and available for service. The train immediately following also ran in "road manual," but subsequent trains were dispatched through the Tube in automatic mode, including No. 117, the tenth train to enter the westbound Tube after No. 363.
No. 117 came to an emergency stop at 6:06 p.m., just after entering the Transbay Tube, with the operator reporting thick smoke which kept him from determining the exact location. 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. This was unsuccessful, and vent fans were turned on at 6:08 p.m. to attempt to clear the smoke, and the third rail was again powered down at 6:15 p.m. A BART supervisor who had been riding on the train helped gather passengers in the lead car, including one blind passenger.
The Oakland Fire Department responded to the West Oakland station, where nine firefighters and two BART policemen boarded Train No. 900 running in "road manual." No. 900 was forced to stop at approximately 1 mile (1.6 km) into the Tube to remove an auxiliary box cover and a derail bar from the track, and eventually stopped approximately 200 feet (61 m) behind No. 117, where the train operator reported the rear car was on fire with heavy black smoke. Upon reaching No. 117, the responders were separated by the smoke, with one policeman and seven firefighters proceeding into the gallery between the tunnels, and the others were forced to return to No. 900 by the smoke. However, the group in the gallery had left the doors open to the tunnel for the others to follow.
Train No. 111 with over 1,000 passengers on board had been holding at the last San Francisco stop, Embarcadero. At 6:21 p.m., No. 111 moved in automatic mode into the eastbound tunnel adjacent to the stricken No. 117 to rescue passengers, who had been led along the smoke-filled westbound tunnel into the gallery. After the rescued passengers boarded No. 111, firefighters searched No. 117 for any remaining passengers, informing central dispatch at 6:59 p.m. that all passengers had been transferred from No. 117 to No. 111. No. 111 immediately proceeded in automatic to West Oakland to transfer passengers to hospitals, but upon accelerating, smoke was drawn from the westbound tunnel through the open doors into the gallery. By this time, more firefighters had responded through the Oakland vent structures, having donned portable oxygen masks with 30-minute supplies. Since the doors to the eastbound tunnel were locked from the gallery side, with smoke filling the gallery, the keyholes were obscured and the firefighters were unable to evacuate to the eastbound tunnel.
The force of the draft from the departing No. 111 knocked the firefighters in the gallery down, and the firefighters began to make their way eastward in the gallery as a single-file human chain, through thick smoke. By this time, their portable oxygen masks were starting to run low, and Lt. William Elliott began to have trouble, requiring assistance from his fellow firefighters. Upon reaching a clear section of the tunnel, another train was dispatched from West Oakland in "road manual" to rescue the firefighters. After the rescue train returned to West Oakland, the firefighters were taken to area hospitals for treatment. Elliott had exhausted his oxygen supply, and died of smoke inhalation and cyanide poisoning.
The fire was declared under control at 10:45 p.m., although the fires were not yet fully extinguished. At approximately 6 p.m. on the following day, January 18, Oakland firefighters responded to flare-up in the gutted train at BART's storage yard. BART would spend US$1,100,000 (equivalent to $3,590,000 in 2015) in tube repairs and safety improvements on top of losing US$1,000,000 (equivalent to $3,260,000 in 2015) in revenue due to the loss of tube service.
BART proposed new evacuation plans to the San Francisco and Oakland fire chiefs by February, but BART service through the Transbay Tube did not resume until April 1979, with California Public Utilities Commissioner Richard D. Gravelle warning "the patrons of BART who utilize its services should be fully aware that the instant order [to reopen service] does not in any way provide a guarantee of safe service." Both the Oakland and San Francisco fire departments criticized BART officials for failing to relinquish control of the emergency situation to the fire departments.
As a precaution, the tube is 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 was reopened just six hours later. Many area highways were damaged by the event, and with the Bay Bridge closed for a month due to a section of the upper deck falling onto the lower deck on a truss section of the east span, the Transbay Tube was the only passable direct way between San Francisco and Oakland.
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). The noise, which according to BART "has been compared to banshees, screech owls, or Doctor Who's TARDIS run amok" is exacerbated by the concrete enclosure and the fact that tracks are curved when the tunnel crosses beneath the San Francisco–Oakland Bay Bridge, causing a high-pitched screeching sound. In 2015, after replacing 6,500 feet and grinding down (smoothing) 3 miles of rail in the tube, BART reported a reduction of noise and positive feedback from riders.
In 2007, as BART celebrated the 50th anniversary of its creation, it announced its plans for the next 50 years. Its vision includes a new separate four-bore Transbay Tube beneath San Francisco Bay that would run parallel to and south of the existing tunnel. The new tunnel would emerge at the Transbay Transit Center to provide connecting service to Caltrain and the planned California High Speed Rail (HSR) system. The four-bore tunnel would provide two additional tunnels for BART trains, and two tunnels for conventional/high-speed rail (the BART system and conventional US rail use different and incompatible rail gauges and operate under different sets of safety regulations). In the terminal, there would be 6 tracks: 4 for HSR and 2 for Caltrain.
During construction, the Transbay Tube was also used briefly as a shooting location for the ending of George Lucas's film THX 1138. The final vertical climb out to daylight was actually filmed, with the camera rotated 90°, in the incomplete (and decidedly horizontal) Transbay Tube. The scene was filmed before installation of the track supports, with Robert Duvall's character using exposed reinforcing bars as a ladder.
The television adaptation of Terry Brooks' Shannara series of books, The Shannara Chronicles, is partly set in the Bay Area, and part of the journey/quest routes the protagonists through the Transbay Tube.
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- on YouTube (starts at 4:30)
|Wikimedia Commons has media related to Transbay Tube.|
- BART History
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- Feaver, Douglas B. (3 June 1979). "Fire Preparedness for Subways". The Washington Post. Retrieved 17 August 2016.
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- Gursoy, Ahmet (1996). "14: Immersed Tube Tunnels". In Bickel, John O.; Kuesel, Thomas R.; King, Elwyn H. Tunnel Engineering Handbook (Second ed.). Norwell, Massachusetts: Kluwer Academic Publishers. pp. 268–297. ISBN 978-1-4613-8053-5. Retrieved 20 August 2016.