San Francisco-Oakland Bay BridgeEdit profile
The San Francisco – Oakland Bay Bridge (known locally as the Bay Bridge) is a pair of bridges spanning San Francisco Bay of California, in the United States. Forming part of Interstate 80 and of the direct road route between San Francisco and Oakland, it carries approximately 270,000 vehicles per day on its two decks. It has one of the longest spans in the world.
The toll bridge was conceived as early as the gold rush days, but construction did not begin until 1933. Designed by Charles H. Purcell, and built by American Bridge Company, it opened for traffic on November 12, 1936, six months before the Golden Gate Bridge. It originally carried automobile traffic on its upper deck, and trucks and trains on the lower, but after the closure of the Key System, the lower deck was converted to road traffic as well.
After being temporarily closed on October 27, 2009, due to failure of the recently repaired eastern span, the Bay Bridge reopened on November 2. For more information, see October 2009 eyebar repair failure and bridge closure.
In 1986, the bridge was unofficially dedicated to James B. Rolph.Composition
The bridge consists of two major crossings connecting each shore with Yerba Buena Island, a natural outcropping located mid-bay. The Western crossing lies between Yerba Buena and San Francisco. It is composed of two complete suspension spans connected at a center anchorage. The top of the Rincon Hill neighborhood serves as the western anchorage and touch-down for the San Francisco landing of the bridge connected by three shorter truss spans. The eastern crossing, between Yerba Buena Island and Oakland, is a cantilever bridge that consists of a double-tower span, five medium truss spans, and a 14-section truss causeway. Due to earthquake concerns the eastern crossing is being replaced by an entirely new crossing, to be finished in late 2013. On Yerba Buena Island, the double-decked crossing consists of a 321 foot (98 m) concrete viaduct east of the west span's cable anchorage, a 540 foot (160 m) tunnel through the island's rocky central hill, another 790.8 foot (241.0 m) concrete viaduct, and a longer curved high-level steel truss viaduct that spans the final 1,169.7 feet (356.5 m) to the cantilever bridge. The viaduct sections east of the tunnel are at present being modified, bypassed and replaced as part of the seismic safety work that will eventually transition traffic onto and off of the self-anchored suspension (SAS) bridge of the new eastern bay crossing.
The toll plaza on the Oakland side (since 1969 for westbound traffic only) has eighteen toll lanes, of which six are dedicated FasTrak lanes. Mainline metering signals are located approximately 600 feet west of the toll plaza. Two full-time bus-only lanes bypass the toll booths and metering lights around the right (north) side of the toll plaza; other high occupancy vehicles are permitted to use these lanes during weekday morning and afternoon commute periods. The two far-left toll lanes are operated as high-occupancy vehicle lanes during weekday morning and afternoon commute periods. During the morning commute hours, traffic congestion on the Oakland approach stretches back onto the three feeder highways, Interstate 580, Interstate 880, and Interstate 80 toward Richmond, California. Since the number of lanes on the San Francisco approach is structurally restricted, backups are frequent in the eastbound direction during evening commute hours. The bridge is currently restricted to motorized freeway traffic. Pedestrians, bicycles, and other non-freeway vehicles and devices are not allowed. A California Department of Transportation (Caltrans) bicycle shuttle operates during peak commute hours for $1.00 each way.
Freeway ramps next to the tunnel provide access to Yerba Buena Island and Treasure Island. Because the toll plaza is on the Oakland side, traffic between the island and San Francisco can freely cross back and forth without ever paying a toll. Those who only travel from Oakland to Yerba Buena Island, and not the entire length to San Francisco, must still pay the full toll.History
San Francisco, located at the mouth of the bay, was in a perfect location to prosper during the California Gold Rush. Almost all goods not produced locally arrived by ship. But after the first transcontinental railroad was completed in May 1869, San Francisco found itself to be on the wrong side of the bay, separated from the new rail link. The fear of many San Franciscans was that the city would lose its position as the regional center of trade. The concept of a bridge spanning the San Francisco Bay had been considered since the Gold Rush days. Several newspaper articles during the early 1870s discussed the idea. In early 1872, a "Bay Bridge Committee" was hard at work on plans to construct a railroad bridge. The April 1872 issue of the San Francisco Real Estate Circular contained an item about the committee:
The self-proclaimed Emperor Norton I saw fit to decree several times that a suspension bridge be constructed to connect Oakland with San Francisco. Later in 1872, frustrated that nothing had happened, Norton decreed:
Unlike most of Emperor Norton's eccentric ideas, his decree to build a bridge had wide public and political appeal. Yet, the task was too much of an engineering and economic challenge since the bay was too wide and too deep there. In 1921, over forty years after Norton's death, a tunnel was considered, but it became clear that one would be inadequate for vehicular traffic. Support for a trans-bay crossing finally grew in the 1920s with the increasing popularity and availability of the automobile. In 1929, the California Legislature established the California Toll Bridge Authority with the responsibility of connecting San Francisco and Alameda County with a bridge.
To make the bridge design feasible, its route was chosen to pass through Yerba Buena Island, significantly reducing the amount of material and construction labor needed to build a trans-bay crossing. Yerba Buena Island was a U.S. Navy base at the time (and until 1997). So the approval of the U.S. Congress, which regulates the armed services and supervises all naval and military bases, was necessary for this island to be used. After a great deal of lobbying, California received Congressional approval to use the island on February 20, 1931.Construction
The chief engineer was Ralph Modjeski. Construction began on July 9, 1933. The western span of the bridge between San Francisco and Yerba Buena Island presented an enormous engineering situation. The bay was up to 100 feet (30 m) deep in places and the soil required new foundation-laying techniques. At the time suspension bridges could not have more than two towers because of stability considerations, and a two-tower span 1.8 miles between anchorages would have been impractical. The solution was to construct a massive concrete anchorage halfway between San Francisco and the island, and to build a complete suspension bridge on each side of the middle anchorage.
The eastern span was a marvelous engineering feat as well. The crossing from Yerba Buena Island to Oakland was spanned by a 10,176-foot (3,102 m) combination of double cantilever, five long-span through-trusses, and a truss causeway, forming the longest bridge of its kind at the time, with the cantilever portion being the most massive one yet constructed.
Much of the original eastern span is founded upon treated wood. Because of the very deep mud on the bay bottom it was not practical to reach bedrock, although the lower levels of the mud are quite firm. Long wooden pilings were crafted from entire old-growth Douglas fir trees which were driven through the soft mud to the firmer bottom layers.Yerba Buena Tunnel
Connecting the two halves of the bridge is Yerba Buena Tunnel, measuring 76 feet (23 m) wide, 58 feet (18 m) high, and 540 feet (160 m) long. It is the largest diameter transportation bore tunnel in the world. The huge amount of rock and dirt excavated from the tunnel was used in part to create Treasure Island in the Bay, immediately north of, and connected to, Yerba Buena Island.
Reminders of the long-gone bridge railway survive along the south side of the lower Yerba Buena Tunnel. These are the regularly spaced "deadman holes" along the wall, into which track workers could duck, in case a train came along while they were in the tunnel. (The north side, which always carried only motor traffic, lacks these holes.)Opening day
The bridge was opened to traffic on November 12, 1936, at 12:30 p.m. Among those in attendance were the former U.S. president Herbert Hoover, Senator William G. McAdoo, and the Governor of California, Frank Merriam. Governor Merriam officially opened the bridge by cutting gold chains across the traffic lanes with an acetylene cutting torch. The San Francisco Chronicle report of November 13, 1936, read:
The total cost of construction for the bridge was $77 million. Prior to its opening, the bridge was blessed by Cardinal Secretary of State Eugene Cardinal Pacelli, who later became Pope Pius XII. At completion, the bridge became the longest suspended-deck bridge in the world and the longest cantilever bridge in the world. Because it was in effect two bridges strung together, the western spans were ranked the second and third largest suspension bridges. Only the George Washington Bridge had a longer span between towers.Roadway plan
The original western approach to (and exit from) the upper deck of the bridge was a long ramp to Fifth, branching to Harrison St for westward traffic off the bridge and Bryant St for eastward traffic entering. There was also an on-ramp to the upper deck on Rincon Hill from Fremont Street (that later became an off-ramp) and an off-ramp to First Street (later extended over First St to Fremont St). The lower deck ended at Essex and Harrison St; just southwest of there, the tracks of the bridge railway left the lower deck and curved northward into the elevated loop through the Transbay Terminal that was paved for buses after rail service ended.
There were three original eastern approaches: a viaduct from the end of Cypress Street (State Route 17) in Oakland; a viaduct from the end of 38th Street (U.S. Route 50) at San Pablo Avenue in Oakland; and the Eastshore Highway which carried U.S. Route 40 along the shoreline of Albany, Berkeley and Emeryville.
Until the 1960s the upper deck (58 ft wide between curbs) carried three lanes of traffic in each direction and was restricted to automobiles only.Eastward view after freeways The lower deck carried three lanes of truck and auto traffic on the north side. In the 1950s traffic lights were added to set the direction of travel in the middle lane, but still with no divider. Two railroad tracks on the south half of the lower deck carried the electric commuter trains of the Southern Pacific, the Key System, and the Sacramento Northern railroad, although train service across the bridge to the San Francisco Transbay Terminal did not begin until January 15, 1939. An overhead catenary supplied power to the Southern Pacific and Sacramento Northern trains while the Key trains used a third rail. After 1941 only the Key System used these tracks; railroad service on the bridge ended in April 1958.
The Bay Bridge rebuilding (five westbound lanes on the upper deck and five eastbound lanes on the lower deck) was completed October 12, 1963.Construction pic Tolls were collected in both directions until September 1969, when toll collection from westbound traffic only began.
The Federal highway on the bridge was originally a concurrency of U.S. Highway 40 and U.S. Highway 50. The bridge was re-designated as Interstate 80 in 1964, and U.S. 40 and U.S. 50 were eventually cut back to Utah and Sacramento, respectively.
The off-ramps for Treasure Island and Yerba Buena Island are unusual in that they are on the left-hand side both in the eastbound and westbound directions. Eastbound and westbound on-ramps are on the usual right-hand side, but they do not have dedicated merge lanes; drivers must accelerate from a stop sign to freeway speeds in a short distance.Modifications
Automobile traffic increased dramatically in the ensuing decades while the Key System declined, and in October 1963, the Bay Bridge was reconfigured with five lanes of westbound traffic on the upper deck and five lanes of eastbound traffic on the lower deck. Trucks were allowed on both decks and the railroad was removed. Owing to a lack of clearance for trucks through the upper-deck portion of the Yerba Buena tunnel, it was necessary to lower the elevation of the upper deck where it passes through the tunnel, and to correspondingly excavate to lower the elevation of the lower portion. This work was done while the Bay Bridge was in use by using a movable temporary span over the portion being lowered. On the lower deck of the tunnel and its eastern viaduct extension, it was necessary to remove central supports, with each transverse beam (of reinforced concrete) being doubled to take the load across all lanes. It was also necessary to further reinforce each beam supporting the upper deck throughout the entire span, modifications still visible to the traveler.
On February 11, 1968, a U.S. Navy T-33 Shooting Star training aircraft, flying out of the nearby Naval Air Station Alameda, crashed into the eastern span of the bridge, killing both officers. One of the truss sections of the bridges was replaced due to damage from the impact.
The series of lights adorning the suspension cables was added in 1986 as part of the bridge's 50th-anniversary celebration.Earthquake damage and subsequent upgrades
During the October 17, 1989, Loma Prieta earthquake, which measured 6.9 on the moment magnitude scale, a 50-foot (15 m) section of the upper deck of the eastern truss portion of the bridge at Pier E9 collapsed onto the deck below, indirectly causing one death. The bridge was closed for just over a month as construction crews repaired the section. It reopened on November 18 of that year. The lighter pavement of the replacement section is visible in aerial photographs, at the east end of the through-truss part of the bridge (37°49′08″N 122°20′39″W / 37.8189°N 122.3442°W / 37.8189; -122.3442 (location of failed span)).Western span retrofitting
The western suspension span has undergone extensive seismic retrofitting. During the retrofit, much of the structural steel supporting the bridge deck was replaced while the bridge remained open to traffic. Engineers accomplished this by using methods similar to those employed on the Chicago Skyway reconstruction project.
The entire bridge was fabricated using hot steel rivets, which are impossible to heat treat and so remain relatively soft. Analysis showed that these could fail by shearing under extreme stress, and so at most locations each was removed by burning out with an oxygen cutting torch, the hole precision reamed and the old rivets replaced with heat-treated high-strength locator bolts and nuts. This work had to be performed with great care as the steel of the structure had for many years been painted with lead based paint, which had to be carefully removed and contained by workers with extensive protective gear.
Most of the beams were originally constructed of two plate I-beams joined with lattices of flat strip or angle stock, depending upon structural requirements. These have all been reconstructed by replacing the riveted lattice elements with bolted steel plate and so converting the lattice beams into box beams. This replacement included adding face plates to the large diagonal beams joining the faces of the main towers, which now have an improved appearance when viewed from certain angles.
Diagonal box beams have been added to each bay of the upper and lower decks of the western spans. These add stiffness to reduce side-to-side motion during an earthquake and reduce the probability of damage to the decking surfaces.
Analysis showed that some massive concrete supports could burst and crumble under likely stresses. In particular the western supports were extensively modified. First, the location of existing reinforcing bar is determined using magnetic techniques. In areas between bars holes are drilled. Into these holes is inserted and glued an L-shaped bar that protrudes 15 to 25 centimeters (6 to 10 inches). This bar is retained in the hole with a high-strength epoxy adhesive. The entire surface of the structure is thus covered with closely spaced protrusions. A network of horizontal and vertical reinforcing bars is then attached to these protrusions. Mold surface plates are then positioned to retain high-strength concrete, which is then pumped into the void. After removal of the formwork the surface appears similar to the original concrete. This technique has been applied elsewhere throughout California to improve freeway overpass abutments and some overpass central supports which have unconventional shapes. (Other techniques such as jacket and grout are applied to simple vertical posts; see the seismic retrofit article.)
The western approaches have also been retrofitted in part, but mostly these have been replaced with new construction of reinforced concrete.Eastern span replacement
The replacement span has undergone a number of design evolutions, both progressive and regressive, with increasing cost estimates and contractor bids. Separated and protected bicycle lanes are a visually prominent feature on the south side of the new east span. The bikeway will carry recreational and commuter cyclists between Oakland and Yerba Buena Island. The opening date for the new span is projected to be in late 2013. The cable bands for the bridge were manufactured in the UK by Goodwin Steel Castings Ltd.
During the 2009 Labor Day weekend closure for a portion of the replacement, a major crack was found in an eyebar, significant enough to warrant bridge closure. Working in parallel with the retrofit, California Department of Transportation (Caltrans), and its contractors and subcontractors, were able to design, engineer, fabricate, and install the pieces required to repair the bridge, delaying its planned opening by only 1½ hours. The repair was not inspected by the Federal Highway Administration, who relied on state inspection reports to ensure safety guidelines were met.
On October 27, 2009, during the evening commute, the steel crossbeam and two steel tie rods repaired over Labor Day weekend snapped off the Bay Bridge's eastern span and fell to the upper deck. The cause may have been due to metal-on-metal vibration from bridge traffic and wind gusts of up to 55 mph causing failure of one rod which broke off, which then led to the metal section crashing down. Three vehicles were either struck by or hit the fallen debris, though there were no injuries. On November 1, Caltrans announced that the bridge would probably stay closed at least through the morning commute of Monday, November 2, after repairs performed during the weekend failed a stress test on Sunday.BART and the Golden Gate Ferry systems added supplemental service to accommodate the increased passenger load during the bridge closure. The bridge reopened to traffic on November 2, 2009.
The pieces which broke off on October 27 were a saddle, crossbars, and two tension rods. For additional details see the Eastern span replacement of the San Francisco-Oakland Bay Bridge article.Name
An unofficial name of the bridge is The James "Sunny Jim" Rolph Bridge — but this name has rarely been used, and it was not widely recognized until the bridge's 50th-anniversary celebrations in 1986. The official name of the bridge for all functional purposes has always been the San Francisco – Oakland Bay Bridge, and by most local people it is widely referred to as simply "The Bay Bridge".
James Rolph, a Mayor of San Francisco from 1912 to 1931, was the Governor of California at the time construction began. He died in office on June 2, 1934, two years before the bridge opened, leaving the bridge to be named for him out of respect. However, due to the opposition of Joseph R. Knowland, publisher of the Oakland Tribune at the time, recognition of Rolph was withheld. In 1932, with an inability to finance the bridge, Joseph R. Knowland, (a former US Congressman) travelled to Washington and helped to persuade President Herbert Hoover and the Reconstruction Finance Corporation to advance $62 million for the building of the bridge.
Emperor Norton's early work at promoting a bridge between the city and county of San Francisco and the city of Oakland and Alameda County was commemorated on December 14, 2004, when the San Francisco Board of Supervisors approved a resolution calling for the new eastern span of the bridge to be named "The Emperor Norton Bridge". The resolution was introduced by San Francisco County Supervisor Aaron Peskin. Neither the city of Oakland nor Alameda County passed any similar resolution.
Plaques honoring the contributions of both Rolph and Norton exist. The Rolph plaque, originally placed at the west end of the bridge in San Francisco, was moved to the corner of Fifth and Bryant Streets in 1986 and removed entirely by Caltrans in 2006. The plaque honoring Emperor Norton for the original idea graced the western archway of the Transbay Terminal, the public transit depot, and the Greyhound bus depot at the west end of the bridge in downtown San Francisco.Financing
When the Bay Bridge opened in 1936, the toll was 65 cents, collected in each direction. Within months, the toll was lowered to 50 cents in order to compete with the ferry system, and finally to 25 cents since this was shown sufficient to pay off the original revenue bonds on schedule. As with other bridges of the era, passage was supposed to become free after completion of the repayment of the original bonds.
In the interest of reducing the cost of collecting tolls and of building additional toll booths, all bridges in the Bay Area were converted to collect tolls in only one direction, with the toll amount collected doubled.
Tolls were subsequently raised to finance improvements to the bridge approaches, required to connect with new freeways, and to subsidize public transit in order to reduce the traffic over the bridge.
Caltrans, the state highway transportation agency, maintains seven of the eight San Francisco Bay Area bridges. (The Golden Gate Bridge is owned and maintained by the Golden Gate Bridge, Highway and Transportation District.)
The basic toll (for automobiles) on the seven state bridges was raised to $1 by Regional Measure 1, approved by Bay Area voters in 1988. A $1 seismic retrofit surcharge was added in 1998 by the state legislature, originally for eight years, but since then extended to December 2037 (AB1171, October 2001). On March 2, 2004, voters approved Regional Measure 2, raising the toll by another dollar to a total of $3. An additional dollar was added to the toll starting January 1, 2007, to cover cost overruns concerning the replacement of the eastern span.
The Metropolitan Transportation Commission, a regional transportation agency, in its capacity as the Bay Area Toll Authority, administers RM1 and RM2 funds, a significant portion of which are allocated to public transit capital improvements and operating subsidies in the transportation corridors served by the bridges. Caltrans administers the "second dollar" seismic surcharge, and receives some of the MTC-administered funds to perform other maintenance work on the bridges. The Bay Area Toll Authority is made up of appointed officials put in place by various city and county governments, and is not subject to direct voter oversight.
Due to further funding shortages for seismic retrofit projects, the Bay Area Toll Authority again raised tolls on all Bay Area bridges (excluding the Golden Gate Bridge) in July 2010. The toll rate for autos on other Bay Area bridges was increased to $5, but in the Bay Bridge a variable pricing tolling scheme based on congestion was implemented. The Bay Bridge congestion pricing scheme charges a US$6 toll from 5 a.m. to 10 a.m. and 3 p.m. to 7 p.m., Monday through Friday. During weekends cars pay US$5. Carpools before the implementation were exempted but now they pay US$2.50, and the carpool toll discount is now also available only to drivers with FasTrak electronic toll devices. The toll remained at the previous toll of US$4 at all other times on weekdays. The Bay Area Toll Authority reported that by October 2010 fewer users are driving during the peak hours and more vehicles are crossing the Bay Bridge before and after the 5-10 a.m. period in which the congestion toll goes into effect. Commute delays in the first six months dropped by an average of 15 percent compared with 2009.Popular culture
The bridge has appeared in many movies, including Shadow of the Thin Man, The Graduate, Koyaanisqatsi, George of the Jungle, 2012, Basic Instinct,The Towering Inferno, and The Dead Pool. The bridge has appeared in the video games Resistance 2, Midtown Madness 2 and Grand Theft Auto: San Andreas. It has also appeared in such science fiction novels as William Gibson's futuristic Bridge trilogy and Cory Doctorow's novel Little Brother, as well as the graphic novel How Loathsome. The new eastern span will appear in the Golden State Warriors logo beginning in the 2011 season.