San Francisco Welcomes Central Subway, Connecting Chinatown to Southeastern Neighborhoods

At the start of 2023, San Francisco’s Central Subway began underground transit operations along Stockton and Fourth Streets, bringing rail service back to Chinatown after a nearly 72-year absence.

The new Central Subway line follows a route that was used by the F-Stockton streetcar line from 1914 until 1951, when the rail service to this part of the city was discontinued and replaced by buses.

The Central Subway connects the South of Market Yerba Buena district to Union Square and Chinatown, adding 1.7 miles to the 5.6-mile Third Street (T-Third) Light Rail Line completed in 2007 by the San Francisco Municipal Transportation Agency (SFMTA). The at-grade T-Third line follows Third Street through the rapidly developing Mission Bay, Bayshore and Hunters Point neighborhoods, ending in Visitacion Valley at the city’s southern limit.

SFMTA contracted WSP USA to design and provide design support during construction for the three underground stations. The firm was also the lead designer for the portal and 1.6 miles of twin, bored tunnel.

“SFMTA’s Central Subway vastly improves transportation through some of San Francisco’s busiest areas,” said Zylah Doria, WSP project manager for the station design package. “By being able to leverage all the knowledge and experience from our joint venture partners, subconsultants and internal staff, we effectively collaborated to find the right solutions for our client.”

“We had an effective partnership with the Central Subway Design Group  during design and design support during construction,” added Nadeem Tahir, project director for SFMTA.

The project has been in the works since the mid-1990’s when San Francisco laid out its long-range plans and phasing for a $2 billion, new core subway and rail infrastructure system to improve north/south and east/west travel through four corridors connecting neighborhoods to the financial district and downtown.

The devastating 1989 Loma Prieta earthquake and the resulting elimination of the Embarcadero Freeway heightened the need to bring rail service to Chinatown and the community rallied to support the project. Funds that would have been used to rebuild the freeway were repurposed towards the Central Subway concept, and construction on the project began with advance utility relocations in 2010 followed by the award of construction contracts for the tunnels in 2011 and the stations, systems and trackwork in 2013.

“It’s a Future Ready® project that began more than 30 years ago and a program that required a great deal of public and political involvement to advance,” said John Fisher, senior managing director for state and local government affairs at WSP. “We are honored to have worked on it for the past 20 years through our incredible partnership with the SFMTA.  This entire project is like a history lesson, and a shining example of how to build better city transit that serves underfunded and underserved communities.”

Central Subway extends the initial 5.6-mile Muni Metro T-Third line — completed in 2007 — by 1.7 miles through the City’s SoMa, Union Square and Chinatown neighborhoods.

In addition to continued service along Third Street to Visitacion Valley at the City’s southern boundary, the T-Third Line now serves residents in the city’s northern corridor at four new stations: the underground Yerba Buena/Moscone, Union Square/Market Street (UMS) and Chinatown-Rose Pak stations, as well as the above-ground 4th and Brannan Station. 

Planned transfer options to the Muni’s bus and trolley network are available at each of the stations and the UMS station provides a direct mezzanine connection to the Powell Street Station, enabling easy transfers to Bay Area Rapid Transit (BART) trains and the Muni Metro Market Street Subway.

Two of the tougher challenges for this project were navigating the constraints posed by the existing Muni and BART tunnels under Market Street for the construction of the tunnels and moving the existing underground utility infrastructure out of the footprint of the stations, especially for the UMS station on Stockton Street where the public right-of-way is 65 feet, which required the construction of a joint utility trench beneath both sidewalks.

“It’s difficult to build within an already established network of utility infrastructure, and that’s one of the reasons why this is the first new subway for San Francisco in so many decades,” Doria said.

Considering its multiple complexities, Doria compared the project to a “pressure cooker” of obstacles and adjustments, but also a “labor of love” that was made possible through a committed team of engineers.

“Facing alignment and surface disruption challenges with the initial 1998 shallow, split alignment along Third and Fourth Streets, WSP’s engineers and its team of subconsultants responded by refining the project’s alignment during the conceptual design phase to Fourth and Stockton Streets,” said Matt Fowler, WSP project manager for the utility relocation and tunnel final design packages. “This allowed for a more direct alignment, consolidation of two stations into one and the use of less surface disruptive tunnel boring machine methods.”

The team also identified appropriate station locations with off street entrances in the dense urban areas, and a tunnel construction worksite under an elevated freeway suitable for 24/7 operations. The project team was able to achieve these objectives while staying within the project’s budget limits.

Fowler said one of the biggest challenges they faced was having to bore the tunnels directly below the BART tunnels on Market Street in order to minimize the depth of the immediately adjacent UMS station. Extensive settlement instrumentation and monitoring  were employed to protect the buildings, utilities and other transportation infrastructure during construction.

“Among the project’s geotechnical innovations was the use of top-down cut-and-cover construction with inclined tangent piles for permanent ground support at the UMS station, as well as the use of inclined compensation grouting pipes to protect pile-supported buildings from tunnel excavation-induced settlements,” Fowler said.

Another priority for WSP and the SFMTA was to add to San Francisco’s sense of community and cultural benefits through this project. To this end, 10 pieces of vibrant art were provided for the four new stations through public funding, including several pieces created by local artists, with two more on their way. 

WSP also worked with several small architecture firms on the underground stations, and the project achieved about 31 percent participation from small business enterprises.

“The end product strongly reflects the support of small businesses for these stations,” Doria said.

During the preliminary design and environmental permitting phase of the Central Subway, the tunnels were cleared to be driven an additional 2,000 feet beyond Chinatown Station to a shallower location along Columbus Avenue in North Beach  to facilitate the retrieval of the tunnel boring machines.

“That tunnel is all about being Future Ready® and preparing for the next steps of providing better service to the residents of San Francisco,” Doria said.

With the completion of this subway line and its official opening on Jan. 7, the local community now has access to some of the liveliest business districts San Francisco has to offer. 

“This is the biggest project I’ve ever worked on, and as a bay area native, I feel extremely proud to be part of the team to bring this project across the finish line, successfully,” Doria said. “It’s an important part of providing equity for the entire community.”

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