San Francisco Central Subway

The 1.7-mile, four-station SFMTA Central Subway will provide light rail transit to the most densely populated area in the U.S. currently without a modern rail transit system.


A Commuting Alternative

By late 2019, riders of the San Francisco Municipal Transportation Agency’s (SFMTA) Central Subway will have a rapid, emission-free alternative to the crowded buses and congested city streets. The Central Subway is a 1.7-mile extension of the Third Street light rail line, known as the T-Third. The Central Subway project includes one surface station between Brannan and Bryant Streets and three underground stations. Two tunnels were constructed and competed in April 2015 using 20.6-foot diameter tunnel boring machines (TBMs). It is San Francisco’s first major subway since the Market Street subway and stations were completed in the 1970s.

Four stations will serve the line:

  • Fourth & Brannan Station (FBS): At-grade station with center-boarding platform along Fourth Street on north side of Brannan Street.
  • Yerba Buena/Moscone Station (YBM): Located at the northwest corner of Fourth and Folsom streets in the SoMa neighborhood, the off-street portion is designed to support future transit-oriented development.
  • Union Square/Market Street Station (UMS): Located in Union Square, with the city’s highest concentration of jobs and many hotels, restaurants and retailers, the station extends from Ellis Street to Geary Street and will be constructed to a depth of over 100 feet, using the top-down cut-and-cover method with inclined and vertical secant and tangent pile walls, large-diameter pipe struts, as well as steel and concrete floor framing.
  • Chinatown Station (CTS): Located at the southwest corner of Stockton and Washington streets, the station headhouse will extend over 100 feet below ground. The platform and connection to the headhouse are constructed in soft- and mixed-ground using mined sequential excavation method. The top of the headhouse will be capable of supporting future TOD or public park/open space.

The extension runs along Fourth and Stockton Streets from the existing Third Street light rail platform at Fourth and King Streets to the new Chinatown terminal. It transitions to subway operations at a portal under the Interstate 80 Freeway, and continues along Fourth Street in a twin-tunnel configuration following a deep profile crossing under four Market Street subway tunnels used by Muni Metro and Bay Area Rapid Transit (BART).

The logistical challenges posed by working in a dense urban setting included the Central Subway tunnels crossing immediately below the BART tunnels. This required extensive three-dimensional soil-structure interaction modelling to assess potential settlements and assure BART and SFMTA of its technical feasibility.

Other challenges include:

  • The maintenance of vehicular traffic and pedestrian movement, and access to and operations of adjacent facilities during construction;
  • Relocation and maintenance of utilities during construction, including design and construction of building closure walls where needed;Instrumentation, monitoring and mitigation of potential settlement impacts on adjacent utilities, BART, and buildings;
  • Construction of entrances and connections at high traffic locations without service interruption.
The Central Subway will transform public transportation access to commercial districts and the BART and Caltran regional rail systems, connecting heavily transit-dependent communities along the corridor that previously relied on less efficient trolleys and bus transport.
Matt Fowler WSP Project Manager

Key Numbers

Central Subway Travel Time
7 minutes
Current Bus Travel Time
20 minutes
1.7 miles
New Stations
Passengers per Train
Projected Daily Ridership

Time Saver

Creating rapid north-south rail transit will bring quicker rides and safer, more efficient transit service from the core of the city to its fast-growing southeast neighborhoods. The Central Subway will reduce to 7 minutes what is now a 20-minute bus trip from Muni's station at Fourth and King Streets to Chinatown. Its two-car trains will be able to carry up to 250 passengers, as compared to the 60 or so carried on a 40-foot bus.

The Central Subway is also key to the economic revitalization of Chinatown, which was weakened economically after the 1989 Loma Prieta earthquake closed the nearby Embarcadero Freeway. Upon opening, the projected ridership along the entire T Third Line will be 43,700 daily boarding, and by 2030, it is projected to reach 65,000 customers per day.

During the Central Subway’s preliminary engineering phase, WSP USA led the joint venture that provided:

  • Evaluation of various tunnel construction methods;
  • Relocation of underground utilities;
  • Preliminary design of the four stations;
  • and tie-in to the surface line at Fourth and King Streets.

Services included:

  • Preliminary engineering and Final Design
  • Environmental Assessments
  • Alignment Evaluations
  • Tunnel and Station Construction Method Studies
  • Portal and Station location evaluations
  • Construction cost estimating and scheduling
  • Tunnel lining design
  • Soil Structure Interaction Analysis
  • Cut-and-cover station design
  • Seismic design
  • Safety and security
  • Fire/ Life safety and ventilation

The Central Subway Design Group joint venture, with WSP in the lead, is responsible for the final design and design support for the three underground stations now under construction at Yerba Buena/Moscone, Union Square/Market Street and Chinatown.

The joint venture provided engineering, cost estimating and environmental studies, which led to the issuance of a Record of Decision (ROD) from the Federal Transit Administration (FTA). Also key to the project’s success was a strong public involvement program.