Since first opening the Transbay Tube for revenue service on September 16, 1974, more than 886,505,820 patrons have made the 3.6-mile underwater trip. Overall, 1,828,033,556 patrons have been carried over $19.2 billion miles by BART trains since initial start-up on September 11, 1972. Today, about 48.5 percent of Transbay peak hour travel is handled by BART through the tube. Fascinating History The concept of an under-the-San Francisco Bay tube has been around for many years, In October 1920, Major General George T. Goethals, the builder of the Panama Canal, make public his proposal for building such an underwater tube "in order to solve the acute transportation problems facing San Francisco and East Bay communities," as the story in a San Francisco newspaper stated. The alignment of Goethal's proposed tube is almost exactly the same as BART's Transbay Tube. Some 20 years after Goethals' proposal was unveiled, a joint Army-Navy Commission in 1947 issued a report recommending that an underwater tube be built in order to relieve the automobile congestion, which was already occurring on the San Francisco-Oakland Bay Bridge, after the bridge had been open for only ten years. The joint commission's proposal called for two bores to carry electric trains going in each direction, as compared to Goethals' proposal, which envisioned a two-level tube to accommodate automobiles, trucks and trains. It must be remembered that General Goethals' proposal was made before the bridge was a reality. BART's Transbay Tube has been acknowledged the world over as one of history's most outstanding civil engineering achievements. Stretching 3.6 miles along the floor of the San Francisco Bay between Oakland and San Francisco, the tube is the vital link in the BART system. It is both the longest and - at its maximum of 135 feet below the surface - the deepest vehicular tube in the world in service today. Beginning in 1959, six years before the start of construction, seismic studies were conducted and soils data obtained to aid in design and alignment decisions. Although the tube does not cross an active geologic fault, special provisions were made in the design to make the tube flexible to absorb earthquake shocks. One such provision was to cushion the tube, shore to shore, in a trench of soft soil, gravel and mud. Another was to attach the tube to its terminal buildings at either end with flexible connections, akin to giant universal joints, which allow for movement of several inches up or down, in or out, and sideways. Design and Construction Parsons Brinckerhoff-Tudor-Bechtel, BART's general engineering consultants, were charged with design and construction management of the total project. The plan was to build the tube in sections, 57 in all, each averaging 330 feet in length, longer than a football field. These were fabricated on dry-land shipways, at the Bethlehem Shipyards in South San Francisco, from which they were launched, towed into the bay, and sunk in their proper positions. The tube sections resemble huge binoculars in cross-section, 24 feet high and 48 feet wide, with trackways in each bore to carry trains in each direction, and are separated by an enclosed central corridor for pedestrian access, ventilation and utilities. Construction began in the mid-1960s as a joint venture of four large contractors - Peter Kiewit Sons' Co.; Raymond International, Inc.; Tidewater Construction Corp.; and Healy-Tibbitts Construction Co. This was the consortium that operated under the name, Trans-Bay Constructors. Their low bid was $90 million for the tube's basic structure. With an additional $90 million for ventilation structures at either end, 2.8 miles of aerial and subway approaches in Oakland and San Francisco, trackage, final finish work and electrification, the full cost of the project was $180 million in 1970 dollars. The contract called for a demanding two-and-a-half year schedule for completion of the basic structure. This meant maintaining a pace of building and placing two tube sections per month. Subcontracts were let and soon an army of welders set to work fabricating the steel skin of the sections at the Bethlehem Shipyards. First came the tube shell, constructed from 3/8-inch steel plate and reinforced with steel T-beams set six feet apart. The inside of the completed shell was then laced with steel reinforcing bars for concrete. After a section was completed and watertight bulkheads placed at each end, it was launched from the shipways and towed to a nearby dock. Here, about 70,000 square feet, or 4,200 cubic yards of concrete was poured to form the 2.3 foot thick interior walls and track bed. The first of the 57 sections was launched in February of 1967. Barely buoyant after the addition of the concrete, it was towed gingerly out to its assigned position. There it was weighted with 500 tons of gravel ballast placed in bins on top of the section, and slowly lowered into place. Final weight of each section is approximately 10,000 tons. Meanwhile, excavation of the trench was progressing. For this job, the contractors had assembled a small navy of specialized vessels and clamshell dredges to cut a ditch in the bay floor 70 to 100 feet deep, sloping to a 60-foot wide bottom, in all, the contractors removed about 5.7 million cubic yards of material, a considerable earth-moving job even on land, much less 135 feet beneath the water's surface. At the same time, surveyors worked around the clock with construction crews to keep the trench precisely aligned through two horizontal and six vertical direction changes. Using lasers from shore positions, engineers were able to pinpoint the exact position required for the dredge barges. To permit leveling of the tube to exact specifications, the engineers specified that a two-foot layer of gravel bedding be placed along the entire length of the trench. This required some special ingenuity. To place and level the gravel, the contractor specially designed a large "screened barge" 85 feet wide, 240 feet long and floating 44 feet high on pontoons. Installed on top was a traveling bridge which carried the machinery for funneling gravel to the floor, and for moving a box-like leveling device called a "screed." Tube Replacement Once the trench was ready, another specially designed rig had to be built to lower the heavy tube sections into place. It consisted of two barges, connected by means of overhead "bridges," separated just enough to nestle a floating tube section between them. Lowering a tube section in zero-visibility deep water compounded the challenge. Engineers met this challenge by devising a sensitive system of hydraulic controls and strain gauges, permitting operators to monitor the weight on all four corner connections at once and thus keep the giant sections level during descent. This equipment was so sensitive the contractor could control the longitudinal and transverse position of the sections to within an inch. From shore positions, surveyors were able to get an exact fix on each tube's required alignment before lowering sections into place. This was done though the use of a specially devised optical plumb line centered from a temporary lookout tower on the tube section itself. Divers were used to help guide the tubes into position for coupling to the preceding section. The 366-foot barge was furnished with two decompression chambers into which the divers could move promptly upon surfacing. Once in place, each new section was snuggled tightly against the previous one by means of four 50-ton railroad type couplers, hydraulically operated. The procedure was to lower the new section into line about two feet away from a tub section already in place, engaging the couplers, then activating the hydraulic rams to draw the new section tightly against the old section. Once this linkup was completed, a barge-mounted crane packed gravel and stone against the sides of the section to lock it in place. An additional five-foot layer of sand and gravel provides a top protective blanket. Once the sections were joined and sealed by a neoprene rubber gasket around the rim, water trapped between the end bulkheads were bled off. Hydrostatic pressure then exerted enough force to keep the seal tight. Later the bulkheads were removed from inside the structure, and permanent steel connections welded into place. Concrete was added to complete the joint construction. Ventilation Structures Ventilation structures on both sides of the bay act as the terminal points for the tube. Through them, air is drawn into the tube and expelled as trains pass to and from. Also, four huge fans, each nine feet in diameter, clear the air in the tube in case of an emergency. Portions of the ventilation structures also serve as substations to feed traction power into the tube from both ends, and house train control equipment. On the San Francisco side of the bay, the massive ventilation structure is a caisson located approximately 450 feet offshore and protruding 25 feet above the surface. At this point, the Market Street subway joins the tube at a depth of about 80 feet. Today one of San Francisco's major restaurants is located on top of the ventilation structure near the San Francisco Ferry Building. Cathodic Protection System To prevent corrosion of its steel skin from salt water electrolysis, the tube employs a cathodic protection system. This system consists of a series of positively charged anodes placed about 250 feet off both sides of the tube. Each anode is connected to the tube by armored cable. The steel surface of the tube, being negatively charged, attracts the positive ions, thereby preventing corrosion. Calcareous deposits built up on the tube skin, over an estimated 15-year period, will offer a protective coating and lessen the cathodic protection current requirements. Completed and Operating The last of the 57 sections of the tube - tube #23 - was launched and placed just east of Yerba Buena Island in April 1969, meeting the required schedule. Track laying, electrification and installation of train control equipment and ventilation were completed by early 1973. On August 10, 1973, the first powered, automatically controlled non-revenue train made the first round trip through the tube. Beginning in 1973, the tube was used regularly as a testing ground for shuttling trains back and forth for BART's San Francisco service, although passengers were not permitted to ride the trains pending authorization by the California Public Utilities Commission. On the morning of September 16, 1974, a seven-car train (Train #101 - Lead car #237) departed Hayward Yard at 4:52 a.m. This train made all stops between Fremont and its destination of Daly City. The Train Operator was Isaac Rodrigues of Hayward. Today, #237 is still in service, with one minor modification. In December 1980, after minor surgery, #237 (A-car) became car #809 (B-car) and has logged on 50,904 hours. It was reported that over 6,000 persons rode BART trains through the Transbay Tube on opening day of service. BART Transbay Tube Facts: • Basic Structure: The longest underwater rapid transit tube in the world in service today. • Route: From underneath the Ferry building in San Francisco across the floor of the bay to the old Oakland mole are which was used by Southern Pacific. This was the route used by ferry boats between San Francisco and Oakland. • Length: 3.6 miles in tube; 6 miles overall, including San Francisco and Oakland approaches. • Depth of Tube: Deepest point, 135 feet below surface of bay; entire line back filled in trench. • Outer Dimension: Each double-barreled section - 48 feet wide, 24 feet deep, with an approximate displacement of 10,000 tons. • Fabrication: Fifty-seven (57) sections of tubular steel and reinforced concrete, each averaging 330 feet in length. • Concrete: Each tube section was towed to a nearby dock where about 70,000 sq. ft., or 4,200 cu. yds., of concrete was poured to form the 2.3 ft. Thick interior walls and track bed. • How Positioned: Each section built and sealed at a local shipyard, floated into line and placed in a trench on floor of bay. • Dredging & Cover: Approximately 5.7 million cu. yds. of bay floor was dredged to create a trough into which the sections of the tube were laid; 1.3 million cu. yards was used as a back fill. • Utilities: Center duct for ventilation and utility lines. • Financing: Toll revenues from San Francisco bay bridges. • Cost of Project: $180 million (1970 dollars). • Travel Time: Embarcadero BART Station, San Francisco, to Oakland's 12th Street/City Center BART Station -12 minutes. • Completion Dates: The 57th section in place, April, 1969; first revenue train, September 16, 1974. Transbay Tube Patronage Calendar Percent Year Transbay Total of Total 1974* 3,967,995 12,987,525 30.6 1975 13,618,777 31,088,619 43.8 1976 13,837,648 34,023,973 40.7 1977 15,516,144 35,715,462 43.4 1978 18,491,468 41,665,638 44.4 1979 10,831,665 31,719,932 34.1 1980 20,376,396 45,275,848 45.0 1981 24,673,582 20,215,531 49.1 1982 27,609,402 54,076,603 51.0 1983 28,140,583 55,519,453 50.0 1984 29,772,230 59,768,054 49.8 1985 30,257,359 61,413,406 49.3 1986 27,554,523 56,350,078 48.9 1987 27,591,443 56,707,239 48.7 1988 28,448,119 58,810,443 48.4 1989 33,144,638 65,938,979 50.3 1990 34,190,517 71,225,552 48.0 1991 34,613,739 72,355,298 47.8 1992 35,052,109 73,753,340 47.5 1993 35,126,525 73,519,400 47.8 1994 34,589,636 72,471,562 47.7 1995 34,540,305 71,792,660 48.1 1996 36,005,188 74,172,922 48.5 1997 36,041,971 75,130,866 48.0 1998 37,829,619 79,346,851 47.7 as of 6/99 19,281,008 40,751,970 47.3 Total: 691,102,587 1,426,154,365 48.5 BART's Transbay Tube Chronology of Events October 17, 1920 General George W. Goethals, Panama Canal building, transbay tube plan proposed. January 1947 Joint Army-Navy commission recommends action for transit line beneath waters of San Francisco Bay. June 1957 California Legislature approves creation of five-county Bay Area Rapid Transit District. November 1957 District officially activated with first Directors' meeting. April 1962 San Mateo County officially withdraws from District. May 1962 Marin County officially withdraws from the District. February 1967 The first section of the Transbay Tube was placed in position. April 1969 Last section (Section #23) of the Transbay Tube was placed into position. June 1971 Last of system's mainline rail set into place on the Contra Costa line. September 11, 1972 BART opened first 26 miles of system between Fremont and MacArthur Stations. January 29, 1973 Richmond-Berkeley line opened, adding 11-miles to the system. May 21, 1973 Concord line opened, adding 17-miles between MacArthur Station and east Contra Costa County. August 10, 1973 First non-revenue train traveled though the Transbay Tube from East Bay to Montgomery Street Station, averaging 70 mph westbound and 80 mph eastbound. November 5, 1973 Service begun between Montgomery Street Station and Daly City Station, bringing into operation a total of 63.5-miles of the 71.5-mile system. September 14, 1974 Ceremonies inaugurating service in the Transbay Tube held at Powell Street Station. September 16, 1974 First train in regular revenue service to operate in the Transbay Tube departed Fremont Station at 6 a.m. This was Train #101, with A-Car #237 as the lead car of this seven-car train. January 17, 1974 A train caught fire in the Transbay Tube which resulted in the tube closing for 12 weeks and the launching of a major fire safety program systemwide including the refurbishing of the entire fleet of BART transit cars with fire resistant materials. April 15, 1979 Transbay Tube reopened for revenue service. September 14, 1984 Celebration of 10 years of service at Powell Street Station. September 16 , 1984 First decade of service. More than eight times the population of the State of California or over 195 million passengers have been carried through the Transbay Tube. November 15, 1989 BART's Transbay Tube reached a record high of 228,480. Thousands of commuters switched to BART to get to and from work after the October 17 earthquake that rocked the San Francisco Bay Area. September 16, 1994 Transbay Tube celebrates 20th anniversary with an anniversary party and special Tube tour. October 16, 1995 BART's new train schedule goes into effect. The new schedules will add five trains, increasing the number of trains during peak hours to 50 from 45 and increasing the frequency of trains operating through the Transbay Tube to as little as 2.5 minutes from 3 minutes. May 2, 1996 BART engineers demonstrate trains operating under the Advanced Automatic Train Control (AATC) system. AATC converts the U.S. military's radio position locating technology, which was successfully used during the Persian Gulf conflict in tracking equipment and troops, to pinpointing a speeding BART train to within 15 feet of its location - including inside the Transbay Tube. September 16, 1999 Transbay Tube celebrates 25th anniversary. A celebration was held at the 12th Street/City Center BART Station.