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}} The San Francisco–Oakland Bay Bridge (known locally as the Bay Bridge) is a complex of bridges spanning San Francisco Bay in California. As part of Interstate 80 and the direct road between San Francisco and Oakland, it carries about 240,000 vehicles a day on its two decks.〔〔 It has one of the longest spans in the United States. 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 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 transit lines, the lower deck was converted to road traffic as well. In 1986 the bridge was unofficially dedicated to James Rolph. The bridge has two sections of roughly equal length; the older western section, officially known as the Willie L. Brown Jr. bridge, connects downtown San Francisco to Yerba Buena Island and the newer unnamed eastern section connects the island to Oakland. The Willie Brown bridge (west span) is a double suspension bridge with two decks, westbound traffic is carried on the upper deck and eastbound on the lower deck. Originally, the largest span of the original eastern section was a cantilever bridge. During the 1989 Loma Prieta earthquake, a section of the eastern span's upper deck collapsed onto the lower deck and the bridge was closed for a month. Reconstruction of the eastern section of the bridge as a causeway connected to a self-anchored suspension bridge began in 2002; the new bridge opened September 2, 2013 at a reported cost of over $6.5 billion.〔(【引用サイトリンク】url=http://abcnews.go.com/US/wireStory/64b-sf-oakland-bay-bridge-opens-traffic-20139554 )〕 Unlike the west span and the original east span, the new east span is a single deck with the eastbound and westbound lanes on each side making it the world's widest bridge, according to ''Guinness World Records'', as of 2014. ==Composition== The bridge consists of two crossings, east and west of Yerba Buena Island, a natural mid-bay outcropping inside San Francisco city limits. The Western crossing (the Willie L. Brown Jr. Bridge) between Yerba Buena and downtown San Francisco has two complete suspension spans connected at a center anchorage. Rincon Hill is the western anchorage and touch-down for the San Francisco landing of the Brown bridge connected by three shorter truss spans. The eastern crossing, between Yerba Buena Island and Oakland, was a cantilever bridge with a double-tower span, five medium truss spans, and a 14-section truss causeway. Due to earthquake concerns, the eastern crossing was replaced by a new crossing that opened on Labor Day 2013. On Yerba Buena Island, the double-decked crossing is a concrete viaduct east of the west span's cable anchorage, a tunnel through the island's rocky central hill, another concrete viaduct, and a longer curved high-level steel truss viaduct that spans the final to the cantilever bridge.〔"Yerba Buena Crossing (Contract No. 04-5)As Built Drawings" Caltrans 2006〕 The viaduct sections east of the tunnel are 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 FasTrak-only. Metering signals are about 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 can use these lanes during weekday morning and afternoon commute periods. The two far-left toll lanes are high-occupancy vehicle lanes during weekday commute periods. During the morning commute hours, traffic congestion on the Oakland approach stretches back to 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 Willie Brown bridge portion of the bay bridge is currently restricted to motorized freeway traffic. Pedestrians, bicycles, and other non-freeway vehicles and devices are not allowed to cross this section. A project to add bicycle/pedestrian lanes to the western Brown span has been proposed but is not finalized. 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 the main part of San Francisco can freely cross back and forth without paying a toll. Those who only travel from Oakland to Yerba Buena Island, and not the entire length to the main part of San Francisco, must pay the full toll. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「San Francisco–Oakland Bay Bridge」の詳細全文を読む スポンサード リンク
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