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-Warm Springs 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 (130 km/h), more than double the average 36 miles per hour (58 km/h) speed in the remainder of the system.
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Conception and construction
Early concepts
The idea of an underwater rail tunnel traversing San Francisco Bay was suggested by the San Francisco eccentric Emperor Norton in a proclamation that he issued on May 12, 1872. Emperor Norton issued a second 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 is almost exactly the same as today's Transbay Tube, and called for building on bay mud, which anticipated some of the seismic design aspects of the finished Transbay Tube. Goethals's proposal was estimated to cost up to US$50,000,000 (equivalent to $671,400,000 in 2016). 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.
Construction
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 US$132,720,000 (equivalent to $1,063,680,000 in 2016). Construction was started on the Tube in 1965, and the structure was completed after the final section was lowered on April 3, 1969. BART sold commemorative bronzed aluminum coins to mark the placement 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 (109 to 113 km/h) and returned in six minutes at the full speed of 80 miles per hour (130 km/h), 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 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. Cathodic protection was provided to resist corrosive action from the Bay's salt water.
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.
Configuration
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 273 to 336 feet (83 to 102 m) long. The average length of each section is 328 feet (100 m), measured along the tunnels' bore; sections are 48 feet (15 m) wide, 24 feet (7.3 m) high, and weigh approximately 10,000 short tons (9,100 t) each. 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. Each section of the Tube cost approximately US$1,500,000 (equivalent to $9,800,000 in 2016), based on the US$90,000,000 (equivalent to $587,780,000 in 2016) construction contract. The steel shell is 0.625 inches (15.9 mm) thick, and has just enough strength to support its own weight and resist hoop stresses; an external consultant, Professor Ralph Peck, convinced project engineer Tom Kuesel that thin shells were adequate because the soil loads would naturally form an arch.
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 seismic 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.
Seismic retrofitting
The 3.6-mile (5.8 km) Transbay Tube has required earthquake retrofitting, both on its exterior and interior. The total cost of seismic retrofits was estimated at US$330,000,000 (equivalent to $418,400,000 in 2016) in 2004.
A 1991 study, commissioned at the recommendation of the Governor's Board of Inquiry in the wake of the 1989 Loma Prieta earthquake, found the seismic joints would "likely remain intact and functional after the next earthquake." 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).
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 4-short-ton (3.6 t), 2.5-inch (64 mm) thick plates; once hoisted in place, the plates were bolted to the existing concrete walls and welded together, end-to-end. The contract for US$7,735,000 (equivalent to $8,069,000 in 2016) 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 US$267,000,000 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 is 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.
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 $3,630,000 in 2016) in tube repairs and safety improvements on top of losing US$1,000,000 (equivalent to $3,300,000 in 2016) 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.
Earthquakes
As a precaution, BART's emergency plans dictate that trains stop during an earthquake, except for trains in the Transbay Tube or the Berkeley Hills Tunnel, which proceed to the nearest station. The lines are then inspected for damage, and resume normal operation if no damage is found.
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.
Pedestrians
In October 2012 and August 2013, pedestrians have entered the Tube through the Embarcadero 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.
Equipment failure
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.
Noise
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.
Marine traffic
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 the Tube 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 1,200 feet (370 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.
Future
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 Transbay Tube. The proposed four-bore Transbay Tube 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 Transbay Tube would provide two additional 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). Therefore, in the future Transbay Transit Center, it is proposed that there would ultimately be six tracks: four for California High Speed Rail (HSR) and two for Caltrain.
In media
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.
One of the early sections of Dead Space features a sound sample taken from a ride through the Transbay Tube.
Source of the article : Wikipedia
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