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.

blank spacer image

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.

blank spacer image Chinatown Station visualization
blank spacer image blank spacer image
blank spacer image Union Square station area visualization

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 consisted of 1.5 miles of twin-bore tunnels underneath Fourth Street and Stockton Street, from I-80 to North Beach. Its major components included 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.


2014 was another milestone year for the Central Subway project. Work on the $233 million tunnels contract reached a major milestone in June, when both TBMs, Mom Chung and Big Alma, completed the tunnel bores from the launch box under I-80 to the extraction pit in North Beach. The contractor, a Joint Venture of Barnard/Impregilo/Haley, also completed the construction of the headwalls for the three underground stations and all five cross passages between the tunnels. Work is now concentrating on the tunnel portal under I-280 at 4th and Bryant Streets. Substantial completion of this contract is expected in April 2015.

Work is also proceeding on the largest single construction contract ever awarded by the SFMTA: the $838 million Stations and Systems contract. The contractor, Tutor Perini, will construct the three underground stations, the surface station, and the overall systems for the project. In January, work ramped up at the Union Square station after the removal of the Winter Walk, an urban park and open space which was installed for the holidays. At that station, pile installation has reached completion and work has commenced at the Union Square garage with hazardous material abatement and demolition. Slurry wall installation on the perimeter walls for the Chinatown Station headhouse has been completed in preparation for excavation. At the Yerba Buena/Moscone station the slurry perimeter wall has also been completed and construction has begun on the roof slab. For the surface station at 4th and Brannan Streets, work was started on the cast-in-place drilled piles. As of the end of January, this contract was 26.88% complete. Substantial completion of this contract is scheduled for February 2018.

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.


Central Subway schedule timeline image



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