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Release date: June 7, 2012

*** Press Release ***

2012 Central Subway Tunnel Construction Overview Map (.pdf)

Central Subway Tunnel Fact Sheet (.pdf)

The San Francisco Municipal Transportation Agency (SFMTA), which oversees transportation in the city, today announced that construction of the Central Subway is ramping up this month, with major work to prepare for tunneling, including excavation of almost an entire city block, commencing next week in SoMa. This new stage of construction will be the first to build permanent elements of the Central Subway, kicking off the next phase of progress on this critical transit project.

On June 12 tunneling contractor Barnard Impregilo Healy Joint Venture will begin excavating and constructing a launch box at the site where tunneling will begin. The launch box will be built on 4th Street between Bryant and Harrison streets, beneath the I-80 overpass. At nearly 500 feet long, 50 feet wide and up to 40 feet deep, this major excavation will take up most of the block. Next year a pair of tunnel boring machines (TBMs) will start digging the Central Subway tunnels from the launch box, traveling north under 4th Street and then Stockton Street.

This year tunnel preparatory work will also take place at several other locations along the project alignment. In addition to the launch box, the tunneling contractor will construct below-ground walls, called headwalls, at two subway station sites, relocate utilities and perform ground-stabilization work to prepare for construction of the Central Subway tunnel.

Work to prepare for headwall installation, including potholing and utility relocation, is planned to begin this week on 4th Street between Folsom and Howard streets, at the site of the future Yerba Buena/Moscone Station. Headwall installation, which involves major excavation work and will require the use of heavy machinery, will soon follow. The walls will be constructed across 4th Street and reach a depth of about 100 feet.

“Crews will soon be building the first permanent components of the vital Central Subway extension of the T Third Line. This $233 million contract will create jobs—both directly and indirectly—and contribute to the local economy,” said Edward D. Reiskin, Director of Transportation. “The launch box will become the portal where T Third Line trains will descend to the Central Subway tunnel, and the headwalls will be integrated into two new subway stations. This work kicks off an exciting new phase for this essential upgrade of San Francisco’s public transportation system.”

Construction will take place at multiple locations on a staggered schedule. Frequent construction updates, including information about traffic, Muni and pedestrian impacts, will be available online on the Central Subway blog (, on Twitter (@Central_Subway) and on Facebook (

Central Subway Tunnel: Summary of Preparatory Work

Those traveling, working and living in areas impacted by Central Subway construction can expect to see large construction equipment as well as an increase in noise, dust and truck traffic while work is in progress. The Central Subway team will continue to work closely with communities, local businesses and organizations to inform them of construction impacts and to ensure appropriate mitigation measures are in place. As work commences at new locations along the alignment, additional information on local impacts will be made available online and in media alerts.

Access to local businesses, residences and driveways will be maintained.

The following tunnel-related work is planned to occur in the coming months:

  • Construction of a tunnel launch box on 4th Street between Bryant and Harrison streets.
  • Installation of below-ground walls, called headwalls, at subway station sites in SoMa and Union Square. Headwall installation will take place on 4th Street between Folsom and Howard streets and on Stockton Street between Market and Geary streets.
  • Ground stabilization work, known as jet grouting or compensation grouting, along the project alignment in SoMa and Union Square. This work involves drilling shafts into the ground, monitoring ground conditions and, if necessary, injecting a mud-like substance that acts as a stabilizer.
  • Ongoing communications and outreach are underway to determine a schedule to relocate utilities in North Beach.

Transit Impacts

Several Muni bus routes will be impacted by Central Subway construction. As construction begins at additional locations, additional Muni routes may be impacted.

  • The 30 Stockton and 45 Union/Stockton began re-routing in January around major construction sites in Union Square and SoMa. These re-routes will continue throughout the duration of Central Subway construction.
  • The 8X/8AX/8BX Bayshore Express and 91 Owl will be rerouted in July, and the temporary 8 Shuttle route will be eliminated. Additional information will be available soon online and in media alerts.
  • The 38/38L Geary may experience delays around Union Square.

Traffic Impacts and Suggested Detours

The following describes ongoing traffic impacts at the tunnel launch box site and around Union Square. As construction commences at new locations, additional traffic impact information will be provided.

Launch Box Construction (4th Street between Bryant and Harrison streets):

  • At least two lanes on 4th Street will be open to traffic at all times.
  • All I-80 on- and off-ramps will remain open during the day, but brief nighttime ramp closures may be required.
  • Traffic delays are anticipated. Motorists are encouraged to use the onramp at Harrison and 7th streets as an alternative to access westbound I-80 while launch box construction is in progress. Those traveling to the peninsula may prefer to access the I-280 via 6th Street or Highway 101 via 10th Street.
  • Parking restrictions will be in effect in and around the construction area.
  • The sidewalk may be closed on one side of the street at a time.
  • Electronic messaging boards will be in place and parking control officers and flaggers will monitor and facilitate the flow of traffic as appropriate.

Yerba Buena/Moscone Station Headwall Installation (4th Street between Folsom and Howard streets):

  • At least two lanes on 4th Street will remain open to traffic while work is in progress.
  • Sidewalks on the west side of the block will be impacted.
  • Access to Clementina Street between 4th and 5th streets may be restricted at times, but the contractor will facilitate access for deliveries.
  • Parking restrictions will be in effect in and around the construction area.
  • Electronic messaging boards will be in place and parking control officers and flaggers will monitor and facilitate the flow of traffic as appropriate.

Construction around Union Square (Stockton Street between Market and Post streets):

  • Work to relocate utility lines to prepare for construction of the Union Square/Market Street Station is ongoing and expected to be completed this summer. Construction to prepare for the Central Subway tunnel will commence soon afterward.
  • Currently, traffic on Stockton Street between Market and Post streets is limited to Muni buses, taxis, tour buses, emergency vehicles and delivery trucks only.
  • Starting this summer, it is anticipated that this section of Stockton Street will be closed to all traffic except emergency vehicles and store delivery trucks.
  • Ellis, O’Farrell, Geary and Post streets will remain open, but temporary lane closures may be required.
  • Suggested detours around Union Square construction are shown on this map, which can be viewed and downloaded on the Central Subway Project blog.

About the Central Subway Project

The Central Subway Project will extend the T Third Line from the 4th Street Caltrain Station to Chinatown, providing a direct, rapid transit link from the Bayshore and Mission Bay areas to SoMa and downtown. Four new stations will be built along the 1.7-mile Central Subway Project alignment – a street-level station at 4th and Brannan streets and three subway stations: Yerba Buena/Moscone Station, Union Square/Market Street Station and Chinatown Station.

Travel times through this busy corridor will be significantly reduced by the Central Subway. During peak hours, current travel between Stockton and Washington streets and 4th and King streets takes more than 20 minutes on Muni trolley coach routes. On the Central Subway, the same trip will take less than eight minutes.

The Central Subway Project is the second phase of the SFMTA’s Third Street Light Rail Transit Project. The first segment of the T Third Line opened in April 2007, restoring light rail service to a high transit-ridership area of San Francisco for the first time in 50 years.

The Central Subway is expected to open to the public in 2019.

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