The Central Subway is a Muni Metro light rail tunnel in San Francisco, California, United States. It runs between Chinatown station in Chinatown and a portal in South of Market (SoMa), with intermediate stops at Union Square/Market Street station in Union Square and Yerba Buena/Moscone station in SoMa. A surface portion runs through SoMa to connect to the previously existing T Third Street line at 4th and King station.

The project was initiated after the Embarcadero Freeway was demolished following the 1989 Loma Prieta earthquake, as activist Rose Pak "almost single-handedly persuaded the city to build" the Central Subway to compensate Chinatown for the loss of the fast cross-town connection. Originally set to open in late 2018, the subway initially opened with a weekend-only shuttle service between Chinatown station and 4th and Brannan station on November 19, 2022. Full service as part of the T Third Street line began on January 7, 2023. With the addition of the Central Subway, the T Third Street line is projected to become Muni Metro's highest ridership line by 2030.

The budget to complete the Central Subway was $1.578 billion. The project was funded primarily through the Federal Transit Administration’s New Starts program. In October 2012, the FTA approved a Full Funding Grant Agreement, the federal commitment of funding through New Starts, for the Central Subway for a total amount of $942.2 million. The Central Subway was also funded by the State of California, the Metropolitan Transportation Commission, the San Francisco County Transportation Authority and the City and County of San Francisco.

Design The tunnel is about long, including of non-revenue tail tracks, and includes three subway stations; the surface tracks built as part of the project are long and include one surface station. These surface tracks begin at 4th and King and continue northwest along 4th Street to 4th and Brannan station. The line enters the Central Subway at a portal under the Interstate 80 viaduct. Yerba Buena/Moscone station is located under 4th Street at Folsom Street. At Market Street, the subway crosses under the Market Street subway, with a reverse curve to align under Stockton Street. Union Square/Market Street station is located under Stockton Street between Market Street and O'Farrell Street, with an outside-fare-control connection to Powell Street station. The line continues north to Chinatown station at Washington Street. The twin subway tunnels continue north under Stockton Street and terminate under Columbus Avenue near Union Street, where the opportunity for extracting the excavators existed.

The platforms of all stations on the Central Subway can only accommodate two-car trains, limiting the capacity of the line.

Cost

In 2000, the estimated cost of the Central Subway project was $530 million. By 2001, the cost had risen to $647 million and completion was projected for 2009. When construction began in 2012, the cost had reached $1.6 billion. When the main contract for Central Subway construction was awarded in May 2013 to the lowest bidder, Tutor Perini, the $840 million contract was up to $120 million over the budgeted amount, which took up nearly two-thirds of the entire project's contingency.

Due to the capital cost ($1.578 billion for the 1.7 mile light rail line), the Central Subway project has come under criticism from transit activists for what they consider to be poor cost-effectiveness. In particular, they note that Muni's own estimates show that the project would increase Muni ridership by less than 1% and yet by 2030 would add $15.2 million a year to Muni's annual operating deficit.

Previous transit access to these areas was provided entirely on the surface through small blocks that feature intense pedestrian activity and narrow streets with multi-modal street congestion. Other, lower-cost rapid transit options were explored, such as bus rapid transit (BRT), but were rejected in part because these conditions do not support the basic features of efficient BRT operations. Compounding these conditions is the fact that many Chinatown residents are transit-dependent and do not own cars, helping rationalize funding for a subway. The high-ridership Muni bus lines serving Chinatown (e.g., the 1 California and the 30 Stockton) are typically over capacity.

In October 2012, the Federal Transit Administration (FTA) announced it would provide $942.2 million for the project under its New Starts program after indicating it would approve the grant in January. This award included the recognition that better, more comfortable service for an already intensively-used transit corridor, particularly for low-income residents as in Chinatown, justifies the investment even if it does not attract a high percentage of "new" riders the way a new rapid transit investment might somewhere that is not already served by extremely slow, uncomfortable high-ridership local service.

Construction A study released in 2000 called for the Central Subway as part of a larger plan to alleviate projected traffic gridlock which also included a light rail line along Geary. Voters approved the Central Subway in 2003, and the alignment was selected in 2008. Ground was broken for the project on February 9, 2010, however, physical work did not begin until June 2012. The first phases of work included preparation of the tunnel boring machine launch site and headwalls for the Yerba Buena/Moscone Station. At the time, the FTA grant had not been secured, and opponents were threatening lawsuits over potential disruption to traffic and businesses.

Tunnel boring

The two tunnel boring machines (TBMs) are named "Big Alma" and "Mom Chung" (for "Big" Alma Spreckels and Dr. Margaret "Mom" Chung, respectively). Preparations for tunnel boring began on June 12, 2012, with the start of excavation for the TBM launch box on Fourth Street between Bryant and Harrison. "Mom Chung" was delivered to San Francisco in April and May 2013, and in late July 2013, "Mom Chung" began digging the tunnel for southbound T Third trains. "Big Alma" began digging north in November 2013 at a slightly faster rate, , compared to the average of "Mom Chung".

The initial plan was to remove the two TBMs near Washington Square in North Beach in 2014 once boring was complete. On July 31, 2012, a lawsuit was filed in Superior Court by Marc Bruno and Save North Beach, a 501(c)(4) organization of North Beach merchants and residents who believed that the removal of the equipment on Columbus Avenue would cause permanent harm to the neighborhood near Washington Square. The petitioners pointed out in their suit that they are in favor of the city's "Transit First" policy and that they would favor the removal of the equipment if a subway stop was planned, approved and financed for their neighborhood. Muni General Manager Ed Reiskin announced a plan in December 2012 to extend the tunnel to Columbus and Powell, using the site of the long-closed Pagoda Palace theater to extract the TBMs, with a potential option to purchase the Pagoda as the site of a future North Beach station. In 2013, MTA reached a lease agreement with the owners of the Pagoda to tear down the old building and use its site for TBM removal. This will reduce impact of construction on the public space.

On June 11, 2014, "Big Alma" broke through to the North Beach extraction shaft at Columbus and Powell Street in North Beach, joining "Mom Chung", which had arrived on June 2. The arrival of the TBMs marked the completion the boring operation phase. The two TBMs were to be disassembled and removed, and the extraction shaft filled in by the end of 2014. The twin tunnels were fully complete by May 2015, when Mayor Ed Lee toured the project underground. Each completed tunnel is long and in diameter, supported by 1,750 concrete rings placed during the boring operation.

Two of the three underground stations were constructed using cut-and-cover methods while Chinatown station was constructed with the sequential excavation method.

Schedule

Just before construction began in 2012, the start of revenue service on the Central Subway extension was scheduled for December 2018. When the main contract was awarded to Tutor Perini in May 2013, schedule float (the amount of time set aside for delays) was reduced from 14.8 months to 5.2 months. In 2014, the San Francisco Controller's Office audited the project and predicted it would be completed on schedule in December 2018 and slightly under budget. Tunnel boring completed in June 2014, a month ahead of schedule and under budget.

Over Labor Day weekend 2015, between September 5–8, the track at the intersection of 4th Street and King Street was extended, which temporarily shortened the services of T Third Street between 4th and King station (referred to as 4th and Berry in the notice) and Sunnydale station; the K Ingleside route also ended at Embarcadero Station and did not splice with the T Third Street route. A similar shutdown was imposed in early November 2015. During the November shutdown, bus service was provided in lieu of the T-Third trains between Embarcadero and Sunnydale; E-Embarcadero service was suspended for two weekends; K-Ingleside again terminated at Embarcadero; and streets were closed in the vicinity of 4th and King.

Central Subway progress Date Incurred Costs Funding Completion $(M) % $(M) % Date % 2015 Jan 747.65 47.37 1,029.79 65Dec 2018 46.5 Jul 818.77 51.88Feb 2019 — 2016 Jan 893.70 56.62 1,179.79 75May 2019 59 Jul 963.51 61.05Jul 2019 61 2017 Jan 1,025.99 65.01 1,329.79 84Oct 2019 64.8 Jul 1,094.84 69.31Dec 2019 70.6 2018 Jan 1,178.42 74.66 1,479.79 94Nov 2019 74.6 Jul 1,232.29 78.08 1,494.00 95Jan 2020 78.6 2019 Jan 1,305.01 82.68 1,517.99 96Dec 2019 82.5 Jul 1,374.37 87.08 1,534.05 97Feb 2020 86.66 2020 Jan 1,488.51 94.3 1,556.74 98.7Sep 2021 91.2 Jul 1,557.53 98.7 1,578.30 100Dec 2021 92.3 2021 Jan 1,696.57 100.3 1,691 100Spr 2022 93.2 Sep 1,855.17 98.1 1,877.15 100Spr 2022 94.0Notes

A Project Management Oversight Committee report released in mid-2017 reported ten months of delays in construction, pushing back the date of service as late as December 10, 2019. The $76 million contingency fund may be used to expedite completion. The delays were attributed to work on the Chinatown station. In December 2017, Tutor Perini (TPC) circulated a report predicting a fifteen-month delay past December 2019 due to circumstances beyond their control, including hard rock and required utility relocations. TPC is liable for penalties of up to $50,000 per day for late completion beyond December 2019.

Also in December 2017, the Central Subway Program Director, John Funghi, announced he would leave the project for Caltrain, where he headed the Peninsula Corridor Electrification Project starting in February 2018. In April 2018, SFMTA announced that excavation was complete for Chinatown station, which was expected to be the last station completed for the Central Subway in mid-2019. The other underground stations, Yerba Buena/Moscone and Union Square, were scheduled to be completed by the end of 2018 ahead of the then-scheduled December 2019 start of revenue service.