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The Downtown Seattle Transit Tunnel (DSTT), also referred to as the Metro Bus Tunnel, is a pair of tunnels for public transit that run north–south under 3rd Avenue through Downtown Seattle, Washington from 9th Avenue and Pike Street to 5th Avenue South and South Jackson Street. The double-track tunnel and its stations, with the exception of Convention Place, constitute the northernmost section of the Central Link light rail line, continuing south through the Rainier Valley to Seattle–Tacoma International Airport as part of Sound Transit's Link Light Rail network. All five of its stations are also served by buses from King County Metro and Sound Transit Express that leave the tunnel north via Interstate 5, south via the SODO Busway, or east via Interstate 90. The DSTT is the busiest section of the Link Light Rail network, with an average of over 10,000 weekday boardings. It is owned by King County Metro and shared with Sound Transit, having signed a joint-operating agreement after ownership was transferred back to King County in 2002.〔()〕 The Downtown Seattle Transit Tunnel is one of two rail-bus tunnels in the United States, alongside the Mount Washington Transit Tunnel in Pittsburgh, Pennsylvania, which lacks stations. Though proposals for a rapid transit tunnel under 3rd Avenue date back to the 1910s and 1920s, planning for the modern bus and rail Metro Bus Tunnel only began in 1974. The King County Metro Council approved the bus tunnel proposal in November 1983, but construction did not begin until March 1987. The tunnel between Convention Place and Westlake stations was built using the cut-and-cover method, closing Pine Street for 19 months and disrupting nearby retail businesses. The segment from Westlake to the International District was bored with two tunnel-boring machines, heading north from Union Station and finishing within a month of each other. Tests of normal buses and the Breda dual-mode buses built specifically for tunnel routes began in March 1989, with tunnel construction declared complete in June 1990, at a cost of $455 million. Light rail tracks were installed in anticipation of future rapid transit service through the tunnel, later found to be poorly insulated and unusable for Link Light Rail. Soft openings of the five tunnel stations were held from August 1989 to September 1990, with regular bus service beginning on September 15, carrying 28,000 daily trips in its first year of operation. The tunnel was closed on September 24, 2005 for modification to accommodate both buses and Sound Transit's Central Link light rail trains on a shared alignment. Prior to closure, around two dozen bus routes ran through the tunnel. The buses were dual-powered, operating as trolleybuses in the tunnel using electricity from overhead wires and as diesel buses on city streets. It reopened on Monday, September 24, 2007. The two-year closure included retrofits for light rail and other operating system upgrades. A stub tunnel, branching from the main tunnel, was constructed under Pine Street between 7th and Boren Avenues to allow light rail trains to stop and reverse direction and for future extension of Central Link.〔(【引用サイトリンク】title=Pine Street Stub Tunnel )〕 Due to the conversion to light rail, dual-mode trolleybuses can no longer operate in the tunnel. Those buses have already been replaced by Metro's current new fleet of hybrid buses, which produce fewer emissions than standard diesel buses, and, unlike the trolleybuses, require no connection to overhead wires. Since the floor of the tunnel was lowered for the light rail, bus mirrors are now at head height, and there have been concerns that they may strike passengers waiting on the platform. To prevent this, the mirror on the platform side of the bus are equipped with flashing lights and the speed limit in stations has been lowered from . ==Route== The , twin tunnels serve as the northernmost section of the Central Link light rail line, which runs between Westlake Station and International District/Chinatown Station, and the terminus for 15 King County Metro bus routes and a Sound Transit Express bus route, which run between Convention Place Station and International District/Chinatown Station.〔(【引用サイトリンク】url=http://metro.kingcounty.gov/tops/tunnel/tunnel.html )〕 Entrances at the three middle stations are built into nearby buildings and with variable-message signs over the stairs and elevators leading to the mezzanines. There are a total of 11 wheelchair-accessible elevators to the tunnel stations, as mandated by the Title II of the Americans with Disabilities Act and the United States Department of Transportation. As part of the city's public art program that began in 1973, the Downtown Seattle Transit Tunnel and its stations were furnished with $1.5 million in artwork from 25 artists commissioned by King County Metro.〔(【引用サイトリンク】url=http://metro.kingcounty.gov/tops/tunnel/tunnel-stationart.html )〕 The northern portal, accessible to buses at street level from Olive Way and from Interstate 5 via an express lane ramp, is Convention Place Station at the intersection of 9th Avenue and Pine Street near the Washington State Convention Center. Convention Place is the only bus-exclusive station in the tunnel and consists of four sheltered side platforms in a sunken, open-air layover space below street level. Buses enter the tunnel under 9th Avenue, passing under the historic Camlin Hotel before joining the Pine Street Stub Tunnel and its light rail turnback tracks for three blocks under Pine Street. The DSTT enters Westlake Station under Pine Street between 3rd and 6th avenues, located between the Westlake Center shopping mall and Westlake Park. The station consists of two side platforms and features a two-block-long mezzanine with exits to Pine Street and several retailers, including the Westlake Center, Macy's in the former The Bon Marché flagship, and the headquarters of Nordstrom, as well as the King County Metro customer service center. The area around the station is known as the Westlake Hub, with connections to the South Lake Union Streetcar and Seattle Center Monorail in addition to King County Metro and Sound Transit buses. Leaving Westlake Station, the tunnel turns south under Century Square to follow 3rd Avenue and its transit mall through the central business district, parallel to the shoreline of Elliott Bay.〔 Three blocks south of Pine Street, buses and trains enter University Street Station, located between Union and Seneca streets adjacent to Benaroya Hall and 1201 Third Avenue in the financial district. The station consists of two side platforms and has a split mezzanine, with entrances to 2nd Avenue and University Street accessible from the north half, and an entrance to Seneca Street from the south half. From University Street, the tunnel continues under 3rd Avenue for five blocks, entering the Pioneer Square neighborhood and historic district. At this point, 3rd Avenue passes several of Seattle's skyscrapers, including the historic Seattle Tower, Safeco Plaza, Fourth and Madison Building and Wells Fargo Center.〔 Within University Street station, the tunnel passes over the century-old Great Northern Tunnel with a clearance of . Pioneer Square Station consists of two side platforms located between Cherry Street and Yesler Way, with four entrances to nearby streets and Prefontaine Place. The station serves the administrative centers of the Seattle and King County governments, located within walking distance of Seattle City Hall, the Seattle Municipal Tower, the King County Courthouse and the King County Administration Building, as well as other major buildings, including Smith Tower, Columbia Center and Alaska Building. The Seattle Civic Square project at the northeast side of the station will include integrated entrances from the intersection of 3rd Avenues and James Street, but has been on hold since 2009. From Pioneer Square, the tunnel travels down a 5.5% grade to cross under the Great Northern Tunnel at a 45-degree angle near the intersection of 4th Avenue South and South Washington Street, briefly descending below sea level,〔(【引用サイトリンク】url=http://metro.kingcounty.gov/tops/tunnel/ts-pioneer.html )〕 before turning cardinal south into the International District neighborhood.〔〔 At the final tunnel station, International District/Chinatown Station, buses and trains serve two side platforms in a partially enclosed level immediately below a public plaza at Union Station. The station has connections to Amtrak and Sounder commuter rail at King Street Station a block to the west, accessible through the Weller Street Bridge, as well as the First Hill Streetcar on Jackson Street, stopping east of 5th Avenue South. Other nearby attractions to the station include CenturyLink Field to the west and Uwajimaya a block southeast.〔 South of the station, the light rail tracks and bus lanes are separated by railway signals at an underground bus layover and staging area adjacent to the tunnel comfort room for bus drivers. The southern portal of the tunnel is located under the intersection of Airport Way and 5th Avenue South at the western terminus of the Interstate 90 express lanes for high-occupancy vehicles. Light rail trains and southbound buses continue from the tunnel in separated lanes on the SODO Busway, while eastbound buses use a ramp that merges with the Interstate 90 express lanes that will be retrofitted for East Link light rail service in 2023. 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「Downtown Seattle Transit Tunnel」の詳細全文を読む スポンサード リンク
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