Central Subway

Tunnel Boring Machines at the retrieval shaft

The Central Subway is the second phase of the Third Street Light Rail line, which opened in 2007. The Central Subway will extend this line northward from its current terminus at 4th and King Streets to a surface station south of Bryant Street and go underground at a portal under US 101. From there it will continue north to stations at Moscone Center, Union Square—where it will provide passenger connections to the Powell Street Station and BART—and at Chinatown, where the line will terminate. The Central Subway is expected to carry nearly 73,000 passengers a day, making it the second most utilized rail project in the Federal New Starts Program. On March 30, 2010 the Transportation Authority Board adopted a Baseline Budget, Schedule and Funding Plan for the project. Revenue service is scheduled for late 2018.

The total project budget is $1.58 billion, and the San Francisco Municipal Transportation Agency (SFMTA) has identified full funding from a combination of local, state, and federal sources. The primary funding source for the Central Subway is the federal New Starts program. To date, the project has received $137.9 million in funds programmed by the Transportation Authority and $177.4 million in federal New Starts funds. It also received $61.3 million in Prop 1A High Speed Rail connectivity funds.

On October 11, 2012, the SFMTA received the Central Subway project's Full Funding Grant Agreement (FFGA), from the Federal Transit Administration (FTA), the most significant funding-related milestone in the New Starts process The FFGA represents the FTA's official commitment of the $849 million in federal New Starts funds to the project, a major milestone that allowed the project to move forward into the main construction phase.

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Above: Mom Chung and Big Alma, the two tunnel boring machines, emerge at the end of their journey into the retrieval shaft in North Beach. Below: A visualization of the Chinatown Station, and the station area at Union Square. Watch a video of the current state of construction, as of June, 2014. and one highlighting progress on the Central Subway during 2013.

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Final Design was completed in October 2012. It was delivered under three contracts: DP1-Tunnels, DP2-Stations, and DP3-Systems. The project is being delivered in four construction packages, all of which have been awarded: Utility Relocation 1, Utility Relocation 2, Tunnels, and Stations and Systems.  Both utility relocation contracts have been completed and work is underway on the Tunnels contract and the Stations and Systems.

The Tunnels contract was awarded in June 2011, to the Joint Venture of Barnard/Impregilo/Healy. The $233.9 million contract consists of 1.5 miles of twin-bore tunnels underneath Fourth Street and Stockton Street, from I-80 to North Beach. Its major components include tunnel boring machine (TBM) procurement, construction of the TBM launch box and cross passages, construction of extraction shaft and portal, and headwalls for the Union Square and Moscone stations, among other elements. The contractor procured the TBMs from The Robbins Company, headquartered in Solon, Ohio.


2013 was a milestone year for the Central Subway project. Tunneling operations started in July with the launch of the first tunneling oring machine (TBM), named Mom Chung in honor of the first American-born Chinese female physician, who established a clinic in San Francisco’s Chinatown. During the Thanksgiving holiday, Mom Chung crossed under Market Street and the Bay Area Rapid Transit District (BART) tunnel, unnoticed except by the workers operating the TBM. On June 2, 2014, Mom Chung broke through the concrete wall of the retrieval shaft in North Beach, ending excavation of the southbound tunnel. The second TBM, named Big Alma in honor of Alma de Bretteville Spreckels, a San Francisco philanthropist also known as the Great Grandmother of San Francisco, was launched in late October, 2013 to excavate the northbound tunnel. Tunnel boring operations were completed on June 11, 2014.

In addition to the 1.5 miles of twin-bore tunnels underneath Fourth Street and Stockton Street, from I-80 to North Beach, the $233.9 million contract with the Joint Venture of Barnard/Impregilo/Haley included construction of the TBM launch box and cross passages; construction of an extraction shaft and portal; and construction of the headwalls for the stations. As of October 2014, four of the five cross passages have been completed and the contractor is making preparations for the start of the tunnel portal at Fourth and Bryant  Streets, beneath I-80.

In June 2013, the SFMTA gave notice-to-proceed to contractor Tutor Perini for the largest single contract ever awarded by the agency: the $840 million stations and systems contract. With a 27% DBE participation, the contract will construct the three stations and the overall systems for the project. The contractor completed the demolition of the structures at the Yerba Buena/Moscone and Chinatown station sites in 2013 and construction of all three stations is underway.

Transportation Authority staff and project delivery oversight consultants will continue to work closely with the SFMTA project team as the project progresses on the construction phase. Revenue service is scheduled for December 2018.

Project Goals

  • Extend the north-south corridor of MUNI's Metro System
  • Provide shorter travel times for passengers
  • Relieve congestion on the Stockton Street corridor
  • Provide connectivity to a future Geary line.


Download the latest Central Subway Fact Sheet.


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Watch an overview video of the current state of construction, as of October 2014.