Трансбайский туннель: Подводная железная дорога Сан-Франциско и Окленда

Underwater rail tunnel under San Francisco Bay

The Transbay Tube is an underwater rail tunnel that 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 mile (6 km) long, and attaches to twin bored tunnels. The section of rail between the nearest stations (one of which is underground) totals 6 mile (10 km) in length. The tube has a maximum depth of 135 feet (41 m) below sea level. Built using the immersed tube technique, the Transbay tube was constructed on land in 57 sections, transported to the site, and then submerged and fastened to the bottom – primarily by packing its sides with sand and gravel. Opened in 1974, the tunnel was the final segment of the original BART system to open. All BART lines except the Orange 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 short as 2.5 minutes. BART trains can reach their highest speeds in the tube, up to , although trains typically operate at unless trying to recover from a delay.

The idea of an underwater rail tunnel traversing San Francisco Bay from Oakland point was suggested by the San Francisco eccentric Emperor Norton in a proclamation that he issued on May 12, 1872. Emperor Norton issued another proclamation on September 17, 1872, threatening to arrest the city leaders of Oakland and San Francisco for neglecting his earlier proclamation. 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, from the foot of Market St. to the Oakland mole, was almost exactly the same as today's Transbay Tube. 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 A competing bridge and tunnel proposal was advanced in July 1921 by J. Vipond Davies and Ralph Modjeski, closer to the alignment of a proposed Southern Crossing, between Mission Rock and Potrero Point in San Francisco due east to Alameda. Davies and Modjeski were critical of the ventilation issues that would arise from a long combined automobile and rail tunnel, indirectly endorsing the idea of a dedicated tunnel for electric rail traffic. The Davies and Modjeski proposal was joined by twelve other proposed projects to cross the Bay in October 1921, several of which featured rail service through long tunnels. 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. The recommendation was issued in a report undertaken to determine the feasibility of the Reber Plan.

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. The route was deliberately chosen to avoid bedrock as much as possible so the tube was free to flex, avoiding concentrated bending stresses. Design concepts and route alignment were completed by July 1960. A 1961 report estimated the cost of the Transbay Tube at Construction was started on the tube in 1965, and the structure was completed after the final section was lowered on April 3, 1969. 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 to in seven minutes at and returned in six minutes at the full speed of , 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 (1 m) deep. Lasers were used to guide the dredging of the trench and the laying of the gravel foundation, maintaining route accuracy of within for the trench and for the foundation. Construction of the trench required dredging 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 feet (1 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 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 sections that had already been placed underwater, the bulkheads between placed sections were removed and a protective layer of sand and gravel was packed against the sides. 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 has 57 sections; each section ranges from long. To conform with the route, 15 tube sections were curved horizontally, 4 were curved vertically, 2 had horizontal and vertical curves, and the remaining 36 sections were straight. The steel shell is thick, 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 (2 m) long by 3 feet (1 m) high over every third door. which allows six degrees of freedom (translation along and rotation about three axes). As designed, the joints allow movement of up to along the tube's axis and up to vertically or laterally. A restaurant was constructed atop the San Francisco transition structure (vent) on a pier behind the Ferry Building. The Oakland vent structure is located in the middle of a Port of Oakland container yard.

The Transbay Tube has required earthquake retrofitting, both on its exterior and interior. The total cost of seismic retrofits was estimated at in 2004. 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
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. Retrofitting work required the fill to be compacted, to make it denser and less prone to liquefaction. Compaction started in Summer 2006 at the east end of the tube, on property belonging to the Port of Oakland. A 2010 paper concluded the distance the tube would rise due to liquefaction was limited based on model testing of potential liquefaction mechanisms, and questioned the justification for the compaction effort. 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. A vehicle was custom built to handle the , thick plates; once hoisted in place, the plates were bolted to the existing concrete walls and welded together, end to end. The contract for was awarded to California Engineering Contractors for installation. 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. The work, originally estimated to last approximately 14 months, was completed by December 2013, after only 8 months of construction. In December 2016, BART awarded a contract to perform further seismic retrofitting. In this phase, a new steel liner and higher capacity pumps would be installed to reduce the possibility of flooding the tube, as the existing pumps would not be adequate in the worst case seismic event. Work was projected to start in the summer of 2018 and is scheduled to take more than two years to complete. Service through the tube would be reduced or eliminated during the first hour and the last three hours of the service day.

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. Poor communication and coordination had hampered the response, and the lessons learned during the 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). 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. The largest to date was the 1989 Loma Prieta earthquake. During the 1989 earthquake, a train passing through the Tube was ordered to stop, although the operator reported no apparent motion. After inspection, the tube was found to be safe, and was reopened just six hours later, with regular service resuming system wide twelve hours after the quake. 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.

In October 2012 and August 2013, pedestrians entered the Tube through the station, prompting shutdowns and delays in Transbay service. In late December 2016, a man entered the Tube through the portal at Embarcadero station and remained in it for more than an hour; while transit police were searching for him, trains continued to move through the Tube at slow speeds in manual mode.

Service has been disrupted on multiple occasions after trains become stuck in the Transbay Tube, which is partially attributed to aging equipment. In addition to the 1979 fire, while moving through the Tube, a train split and was automatically stopped after a coupler failed in March 2010. Two maintenance vehicles collided within the Tube in September 2014, damaging a section of track and forcing BART traffic to rely on a single track. In January 2015, a train was forced to stop in the Tube after the brake inadvertently engaged on a car. A train in December 2016 was forced to switch to manual mode and proceed at reduced speed after stopping in the Tube, and another faulty brake forced a train to stop in the Tube in April 2017.

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.

Ship traffic passing through the Bay can damage the anodes used in the Tube's cathodic protection system when dropping anchor. Since the anodes protrude from the filled trench surrounding the Tube, they are more vulnerable to damage. Marine traffic is restricted from dropping anchors when over the Tube, but BART conducts routine inspections for anode damage. The Tube was closed briefly on January 31, 2014, after a drifting freighter dropped anchor near it at 8:45 a. m. to maintain position. The Coast Guard notified BART officials the anchor appeared to be close to the Tube at 11:55 a. m., based on the ship's position, leading to a suspension of Tube service for approximately 20 minutes while inspections were conducted. No damage was found, and the Tube was reopened at 12:15 p. m. Harbor pilots later noted the ship had anchored 1200 feet (366 m) southwest of the Tube. Two trains that had been passing through the Tube were stopped in place while the inspection was conducted. Trains were delayed by 15 to 20 minutes, with normal service resuming around 1 p. m.

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 barge came to rest atop the fill overlaying the Transbay Tube, but did not disrupt transit operations. The primary concern was the potential leakage of diesel fuel, and divers had stopped the leak within a day.

In 2007, as BART celebrated the 50th anniversary of its creation, it announced its plans for the next 50 years. Determining the current tunnel will be at its operational capacity by the year 2030, the agency has plans which include a new separate Transbay Tube beneath San Francisco Bay that would run parallel to and south of the existing Transbay Tube. The proposed four bore tunnel would emerge at the Transbay Transit Center to provide connecting service to Caltrain and the planned California High Speed Rail (CHSR) system. The second Tube would provide two tracks for BART trains, and two tracks for conventional/high speed rail (the BART system and conventional U. S. rail use different and incompatible rail gauges and operate under different sets of safety regulations). 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. 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. As of March 2023, a combined four track tunnel or two separate tunnels for both BART and regular rail are no longer considered cost effective due to reduced ridership in the Bay Area; planners will research one single tunnel dedicated to either BART service or regional rail service. CCJPA is considering three possible routes, one for regional rail and two for BART extensions.

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