Mayor Lee and SFMTA Celebrate Central Subway Milestone

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Central Subway TBM Fact Sheet 6.16.14.pdf

Central Subway Tunnel Fact Sheet 6.16.14.pdf

Mayor Edwin M. Lee and the San Francisco Municipal Transportation Agency (SFMTA), which oversees all transportation in the city, including the Municipal Railway (Muni), today celebrated the completion of tunneling work for the Central Subway Project, the major extension of the Muni Metro T Third Line. The two 350-foot-long tunnel boring machines (TBMs) each tunneled 8,500 feet to construct two Central Subway tunnels, which will allow the T Third Line trains to travel quickly beneath SoMa, Union Square and Chinatown when the Central Subway opens in 2019, cutting travel times by more than half along the busy corridor.

“The Central Subway project invests in building a much-needed world-class 21st century transportation system for our world-class city,” said Mayor Lee. “The significance of the Central Subway tunneling work completed today cannot be overstated. Today we move forward on executing our City’s vision of a reliable, modern public transportation system that better connects and better serves our residents, visitors and businesses.”

The 750 ton, identical TBMs are named “Mom Chung” after Dr. Margaret “Mom” Chung, the country’s first female Chinese-American physician and a surrogate mother to thousands of veterans in World War II, and “Big Alma” after 19th century San Francisco philanthropist and socialite “Big Alma” de Bretteville Spreckels. Mom Chung launched in June 2013 and Big Alma followed in November 2013, traveling beneath 4th Street, Stockton Street and Columbus Avenue to excavate and construct San Francisco’s first new subway tunnel in more than 30 years.

“The milestone we reach today is the latest example of how the City of San Francisco is coming together to get big projects done,” said Board of Supervisors President David Chiu “The Central Subway project is a symbol of our commitment to invest in the infrastructure that will empower our city to grow and prosper for generations to come.”

“The tunnels that Mom Chung and Big Alma have built will provide a much-needed connection between major employment, retail, cultural and residential areas of the city,” said Tom Nolan, Chairman of the SFMTA Board of Directors. “Opening in 2019, the Central Subway will ease the congestion we experience on the 4th and Stockton corridors, replacing it with fast, efficient transit that gets people where they need to go.”

“As San Francisco grows, it is imperative that we prepare for that growth by providing fast and reliable transit in areas that otherwise face future gridlock and congestion,” said SFMTA Director of Transportation, Edward D. Reiskin. “The tunneling work we complete today highlights how San Francisco is leading the way in preparing for the future by strategically investing in our infrastructure and prioritizing the transportation needs of our evolving city.”

The TBMs excavated and constructed the Central Subway’s 1.5 mile-long tunnels at an average pace of 40 feet per day and will be retrieved in North Beach at the site of the former Pagoda Palace Theatre on Powell Street. Over the next few months, both Big Alma and Mom Chung will be dismantled and removed from the tunnels to be reused in tunneling efforts in other cities around the world.

The Central Subway is expected to open to the public in 2019 and will significantly decrease travel times along 4th and Stockton streets, two of San Francisco’s most congested corridors, while accommodating job and population growth anticipated in SoMa, downtown, Chinatown and along the existing T Third Line in eastern and southeastern San Francisco. Three subway stations will be built along the route the TBMs will follow:

  • The Chinatown Station, a subway station with an entrance at Stockton and Washington streets;
  • The Union Square/Market Street Station, a subway station with entrances at Stockton and Geary streets and Stockton and Ellis streets;
  • The Yerba Buena/Moscone Station, a subway station with an entrance at 4th and Clementina streets. 

In addition, the project includes a surface-level station at 4th and Brannan streets.

For more information on the Central Subway project, visit To see footage of Big Alma breaking through the end of its tunneling work, please visit: