San Francisco 4th and King Street station in the context of Central Subway (San Francisco)

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.