San Francisco marks subway tunneling launch

San Francisco Mayor Edwin M. Lee on Thursday, May 30, marked the start of tunneling for the Central Subway Project, a controversial extension of the Muni Metro T Third Line (light rail transit).

A 350-foot-long tunnel boring machine (TBM), now nearly assembled under 4th Street, will soon begin tunneling its way north to construct one of the two tunnels included in the Central Subway Project, according to San Francisco MunicipalTransportation Agency (SFMTA).

Said Mayor Lee, “As we start tunneling construction on the Central Subway, I thank our federal, state and local partners for their continued commitment to improving public transit in San Francisco.” Tunneling is expected to be completed in 10 months.

The TBM, named Mom Chung after Dr. Margaret “Mom” Chung, the country’s first female Chinese-American physician and a surrogate mother to thousands of veterans in World War II, is being assembled within an excavation under 4th Street in SoMa. It will launch next month, traveling beneath 4th Street, Stockton Street, and Columbus Avenue to excavate and construct San Francisco’s first new subway tunnel in more than 30 years.

An identical TBM, named Big Alma after 19th century San Francisco philanthropist and socialite “Big Alma” de Bretteville Spreckels, will arrive this summer and launch soon after, constructing a tunnel parallel to Mom Chung’s.

The Central Subway aims to decrease travel times along 4th Street and Stockton Street, two of San Francisco’s most congested corridors, while accommodating job and population growth anticipated in SoMa, downtown, Chinatown, and along the existing T Third Line in eastern and southeastern San Francisco.

Three subway stations will be built along the route, along with a fourth station above ground. One subway stop, Union Square/Market Street Station, will offer transfer capability to the existing Powell Street MUNI/BART station, offering connections to J, K, L, M, and N MUNI lines and BART service on Market Street.

Critics of the construction project have objected to its high cost, with some arguing that a surface LRT route would cost less, serve the same ridershed, and provide more economic support to the neighborhoods the line will serve.