Market Street subway

The Market Street Railway had existed on the surface parallel to the subway's alignment in some form since 1860 with services terminating at the Ferry Building.[3] To alleviate traffic, plans for a tunnel under Market Street can be dated to at least 1912.[4] By 1918, there were four tracks running down the thoroughfare - two per direction.[3] That plan is nearly identical to the design built 60 years later, including two levels of train traffic and provisions for both overhead and third-rail power delivery, but not accounting for a Transbay Tunnel.

The Twin Peaks Tunnel was built with the east end sloping downward, foreseeing future connection to a tunnel under Market Street.[5]

Serious consideration for construction was finally given while designing the initial BART system. Original plans variously called for the current stations, less Embarcadero, with a connection to a (now unbuilt) subway under Geary Street or the existing Twin Peaks Tunnel. The 1961 BART plan called for Muni operations in the subway only between Sansome and Gough Streets and did not have any provisions for the Embarcadero station.[6]

Construction, commencing in July 1967, was carried out via the cut-and-cover method. By this time, Embarcadero station was planned and a station box was constructed with the tunnel, but was not slated to be complete with the initial opening of the subway.

BART trains first ran through the Subway with service as far as Daly City on November 5, 1973.[7] Connections through the Transbay Tube were opened for revenue service on September 16, 1974.[7] Embarcadero station was opened shortly after on May 27, 1976;[7] its design is unique among Market Street BART stations.

Starting on February 18, 1980 and continuing for over a year afterward, Muni replaced surface operations with subway service at all stations in the tunnel. At that point, there were no plans to maintain the street-running tracks on Market Street, but that changed in the late 1980s after the success of several Historic Trolley Festivals. Muni's Embarcadero portal opened in 1998, and was not an original part of the subway's plan; this allowed connections to Caltrain's 4th and King Station. T Third trains began running in the subway with the line's inauguration on April 7, 2007. That line will be rerouted through Central Subway, which is a later-constructed tunnel running underneath the Market Street subway east of Powell Street Station, when completed.

Prior to March 30, 2020, the K Ingleside, L Taraval, M Ocean View, and T Third Street Muni Metro lines ran through the entire length of the subway to its direct connection with the Twin Peaks Tunnel. The J Church and N Judah lines left the subway via the Duboce portal at Church and Duboce streets, and only the N Judah and the T Third Street lines continued past the Embarcadero portal. Since the Muni Metro platforms at Montgomery Street, Powell Street, and Civic Center are long enough to hold two 75-foot (23 m) two-car trains simultaneously, the San Francisco Municipal Transportation Agency began double-berthing in April 2015.[8] Under this process, two trains are in the station at once: the rear train discharges passengers while the front train boards passengers. The new practice was aimed at reducing passenger frustration, though it would not reduce travel times. In 1997 work began to install the SelTrac CBTC-based signalling system in the subway. The work was completed in 2001 and station-to-station operation is now completely automated under normal operation.[9]

On March 30, 2020, Muni Metro service, including trains through the Market Street Subway, was replaced with buses due to the COVID-19 pandemic.[10] Rail service returned on August 22, with the routes reconfigured to improve reliability in the subway. M Ocean View and T Third Street service are interlined, running between Sunnydale station and Balboa Park station; it runs in the subway along with normal N Judah service and increased S Shuttle service. No J, K, or L service enters the subway: J Church service runs only on the surface between Balboa Park station and Church and Duboce station, while K Ingleside and L Taraval service is interlined, running between Wawona and 46th Avenue station and Balboa Park station.[11]

BART headways are short through this segment, as the right of way carries four of the system's five rapid transit lines on just two tracks.

The F Market & Wharves heritage streetcar line, while not a Muni Metro service, runs on the surface for the entire length of the subway with connections at all stations.

Upon completion, the Central Subway will be connected to the Market Street subway via a pedestrian underpass running from the existing Powell Street Station to the under-construction Union Square/Market Street Station a block away. The T will be rerouted from the Market Street subway into the new Central subway.

There are a total of seven stations in the tunnel. Four are used by BART; all seven are used by the Muni Metro lines that had previously run on the surface of Market Street, as well as the T Third Street line until the completion of the Central Subway. The N Judah exits the tunnel at the Duboce portal and thus does not serve Church Street and Castro Street stations.

Stations are listed from the northeast to the southwest.

Station	Platform Layout	Muni Metro	BART
Embarcadero Station	island	M Ocean View (outbound)  N Judah  S Shuttle  T Third Street (inbound)
Montgomery Street Station	island	M Ocean View (outbound)  N Judah  S Shuttle  T Third Street (inbound)
Powell Street Station	island	M Ocean View (outbound)  N Judah  S Shuttle  T Third Street (inbound)
Civic Center / UN Plaza Station	island	M Ocean View (outbound)  N Judah  S Shuttle  T Third Street (inbound)
Van Ness Station	island	M Ocean View (outbound)  N Judah  S Shuttle  T Third Street (inbound)
Church Street Station	side	M Ocean View (outbound)  S Shuttle  T Third Street (inbound)
Castro Street Station	side	M Ocean View (outbound)  S Shuttle  T Third Street (inbound)

Media related to Market Street Subway at Wikimedia Commons