The Downtown Seattle Transit Tunnel (DSTT), formerly also known as the Metro Bus Tunnel, is a pair of public transit tunnels in Seattle, Washington, United States. The double-track tunnel and its four stations serve Link light rail trains on the 1 Line and 2 Line as they travel through Downtown Seattle. The tunnel runs west under Pine Street from 9th Avenue to 3rd Avenue, and south under 3rd Avenue to South Jackson Street. The two light rail lines diverge at International District/Chinatown station to continue south on the 1 Line and east on the 2 Line.
The DSTT was used only by buses from its opening in 1990 until 2005, and shared by buses and light rail from 2009 until 2019. Bus routes from King County Metro and Sound Transit Express left the tunnel north via Interstate 5, south via the SODO Busway, or east via Interstate 90. It was owned by King County Metro and shared with Sound Transit through a joint-operating agreement signed in 2002; Sound Transit assumed full ownership in 2022. The Downtown Seattle Transit Tunnel was one of two tunnels in the United States shared by buses and trains, the other being the Mount Washington Transit Tunnel in Pittsburgh, and was the only one in the United States with shared stations.
Though proposals for a rapid transit tunnel under 3rd Avenue were introduced in 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 access to the retail core. 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; tunnel construction was declared complete in June 1990, at a cost of $469 million. Light rail tracks were installed in anticipation of future rapid transit service through the tunnel, but were later found to be poorly insulated and unusable for Link light rail. Soft openings and public previews 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 passengers in its first year of operation. For the next several years, until June 2004, service in the tunnel was provided exclusively by dual-mode buses, which ran as trolleybuses in the tunnellike the city's extensive trolleybus systemand as diesel buses on surface streets and freeways.
The tunnel was closed on September 24, 2005, for modification to accommodate both buses and Sound Transit's Central Link (now the 1 Line) light rail trains with shared lanes and platforms. The roadway was lowered by and other improvements were made to prepare for light rail service. New hybrid electric buses were moved into the tunnel to replace the Breda fleet, as the overhead wire was replaced for light rail trains. The tunnel reopened on September 24, 2007, and light rail service began on July 18, 2009. A stub tunnel, branching from the main tunnel, was constructed under Pine Street to allow light rail trains to stop and reverse direction; it was later used as the first segment of a light rail extension to Capitol Hill and the University of Washington that opened in 2016. Convention Place station was closed permanently on July 21, 2018, to make way for an expansion of the Seattle Convention Center that would also restrict bus access to the tunnel. On March 23, 2019, bus service in the tunnel ceased and its remaining seven routes were moved to surface streets.
Route and stations
The , tunnel is used by the 1 Line and 2 Line between Westlake and International District/Chinatown stations. Entrances at several tunnel stations are built into nearby buildings with variable-message signs over the stairs and elevators leading to the mezzanines. A total of 11 wheelchair-accessible elevators connect the tunnel stations to the surface. The deepest of the tunnel stations are below street level and consist of two side platforms, two tracks, and a former bus passing lane in the middle. Since 2019, the stations have also had signs with numbered exits to aid in rider wayfinding. 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 (equivalent to $ million in dollars) in artwork by 25 artists commissioned by King County Metro.
The northern portal, formerly accessible to buses at street level from Olive Way, and from Interstate 5 via an express lane ramp, was the former Convention Place station at the intersection of 9th Avenue and Pine Street near the Seattle Convention Center. Until its closure in 2018, Convention Place was the only bus-exclusive station in the tunnel, and consisted of four sheltered platforms in a sunken, open-air layover space below street level. Buses entered the tunnel from 9th Avenue and passed under the historic Camlin Hotel, before joining the University Link Tunnel used by light rail trains headed north for three blocks under Pine Street to Capitol Hill station.
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 features a two-block-long mezzanine with exits to Pine Street and several retailers, including the Westlake Center, the former The Bon Marché flagship store, and the Nordstrom Building, as well as the former 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 the Seattle Center Monorail as well as the King County Metro and Sound Transit buses. Leaving Westlake Station, the bored set of twin tunnels turn 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 Symphony station, located between Union and Seneca streets adjacent to Benaroya Hall and 1201 Third Avenue in the financial district. The station 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 Symphony, 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, the Fourth and Madison Building and the Wells Fargo Center. Within Symphony station, the tunnel passes over the century-old Great Northern Tunnel with a clearance of .
Pioneer Square station is located between Cherry Street and Yesler Way, with four entrances to nearby streets and Prefontaine Place serving two mezzanines. 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 the Alaska Building. 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, before turning cardinal south into the International District neighborhood.
International District/Chinatown station, the southernmost tunnel station, is partially open-air and located 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 attractions near the station include Lumen Field to the west and Uwajimaya a block to the southeast. South of the station, the light rail tracks and bus lanes were formerly separated by railway signals at an underground bus layover and staging area next 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 former Interstate 90 express lanes for high-occupancy vehicles. Until bus operations ceased, southbound routes continued from the tunnel in separated lanes on the SODO Busway, while eastbound buses used a set of ramps that traveled onto the Interstate 90 express lanes. The ramps were retrofitted for the 2 Line, which began service in March 2026.
Service
The Downtown Seattle Transit Tunnel and the surface buses on 3rd Avenue comprise the "Third Avenue Transit Spine", the busiest transit corridor in Seattle. The tunnel's four stations served a total of passengers in 2024 with a weekday average of riders. The nearly 300 daily buses on the surface section of 3rd Avenue carried 52,400 daily passengers in 2022. The tunnel has a theoretical capacity of 40 trains per hour per direction with a minimum of 90-second headways, carrying 22,000 passengers per hour per direction, but is only able to carry 12,000 per hour per direction in 4-car light rail vehicles with current systems in place. Prior to the start of Link light rail service, the DSTT could serve up to 145 buses during the afternoon rush hour. During mixed operations in 2012, the tunnel carried 52,600 daily passengers, of which 10,000 were on light rail trains.
The tunnel carries a shared section of the 1 Line and 2 Line, which continue to other areas of King and Snohomish counties. Trains serve all downtown tunnel stations 20 hours a day every day; during regular weekday service, trains run roughly every 4 to 5 minutes during rush hour and midday operation, respectively, with longer headways of 15 minutes in the early morning and 20 minutes at night. During weekends, 1 Line and 2 Line trains arrive every 10 minutes during midday hours and every 15 minutes during mornings and evenings. Light rail service from Westlake to International District/Chinatown takes approximately seven minutes.
Prior to the cessation of bus service in March 2019, the DSTT was served by seven bus routes that stopped at all four tunnel stations as well as stops near the former Convention Place station. At each station, bus routes were divided into three bays labeled with their general direction. Bay A was served by three routes heading north toward Northgate and the University District and east to Kirkland via State Route 520; Bay C was served by three routes heading south through the SODO Busway toward the Rainier Valley and Renton; and Bay D was served by a single route, Sound Transit Express route 550, heading east to Mercer Island and Bellevue via Interstate 90.
During closures of the Downtown Seattle Transit Tunnel, tunnel buses were rerouted onto 2nd and 4th Avenues between Yesler Way and Pine Street, and Stewart Street and Olive Way between 2nd and Boren Avenues. Metro also runs a special route, the Route 97 Link Shuttle, between all Link light rail stations during service disruptions.
Operations