Market Street subway
| Company type | Transit infrastructure |
|---|---|
| Industry | Public transportation |
| Founded | 1967 |
| Headquarters | San Francisco , United States |
| Products | Subway tunnel for Muni Metro and BART trains |
Market Street subway
The Market Street subway is a dual-level tunnel beneath Market Street in San Francisco, California, accommodating both Muni Metro and BART trains. Extending from Embarcadero station to Castro station, its upper tier is dedicated to Muni Metro services, while the lower tier carries BART trains. Notably, BART trains do not run the entire length of the subway, instead veering southward beneath Mission Street near Civic Center/UN Plaza station. The northeastern segment of the BART level connects directly to the Transbay Tube, whereas the Muni Metro tracks link southwestward to the historic Twin Peaks Tunnel and northeastward to surface lines along the Embarcadero.
Background
Since 1860, the Market Street Railway operated street-level transit parallel to the current subway route, terminating at the Ferry Building. The concept of tunneling under Market Street was proposed as early as 1912 to reduce surface traffic congestion. By 1918, Market Street featured four tracks—two in each direction—mirroring early transit infrastructure. The initial tunnel proposal closely resembled the eventual construction six decades later, envisioning a two-tier train system with accommodations for both overhead and third-rail electric power; however, it did not include a Transbay Tunnel connection.
The Twin Peaks Tunnel was engineered with an eastern incline designed to integrate seamlessly with a prospective Market Street tunnel.
During preliminary planning for the BART system, serious plans were made for a two-level tunnel featuring BART trains on the lower level and Muni streetcars above. The San Francisco Bay Area Rapid Transit District intended full ownership of this tunnel and designed Muni’s platforms with sufficient length to allow future conversion for BART use. Although this plan was ultimately abandoned, construction had already begun, resulting in a light rail subway built to accommodate rapid transit vehicles—a strategy known as premetro. However, before voter approval, the District neither procured compatible streetcar vehicles nor planned for integrating existing lines into the new tunnel.
Construction and operation
Construction commenced in July 1967 employing the cut-and-cover technique. The Embarcadero station was incorporated later; initially, only its structural shell was completed.
BART began operating trains through the subway toward Daly City on November 5, 1973. The Transbay Tube connection opened for passenger service on September 16, 1974, followed by Embarcadero station’s inauguration on May 27, 1976. Early in 1978, a demonstration event featured test runs of Boeing LRV 1221 through the Muni portion of the tunnel.
Starting February 18, 1980, Muni gradually transitioned from surface routes to subway service within this tunnel over more than a year. Initially, streetcar tracks on Market Street’s surface were removed but were preserved following successful Historic Trolley Festivals during the late 1980s. The Embarcadero portal for Muni opened in 1998, facilitating transfers to Caltrain at its 4th and King Station. From 2007 until its relocation to the new Central Subway in 2023, Muni operated the T Third Street line combined with the K Ingleside line through the Market Street Subway. The Central Subway provides an underground pedestrian connection from its new Union Square/Market Street station to Powell Station.
Services
Prior to March 30, 2020, the K Ingleside, L Taraval, M Ocean View, and T Third Street Muni Metro routes operated through the entire subway system, connecting directly to the Twin Peaks Tunnel. The J Church and N Judah lines exited via the Duboce portal; among these, only the N Judah and T Third Street continued beyond Embarcadero station. Montgomery Street, Powell Street, and Civic Center stations feature double-berthing platforms, allowing two two-car trains to be accommodated simultaneously—a strategy introduced in April 2015 aimed at minimizing passenger delays without reducing overall travel times. Between 1997 and 2001, the SelTrac CBTC signaling system was implemented to automate train movements between stations under standard operating conditions.
On March 30, 2020, due to the impact of the COVID-19 pandemic, Muni Metro services—including those running through the Market Street Subway—were replaced by bus operations. Rail service recommenced on August 22 with modified routes designed to enhance reliability: J, K, and L lines no longer entered the subway; J Church operated solely on surface tracks between Balboa Park and Church/Duboce; K Ingleside and L Taraval lines were combined into a single route running between Wawona/46th Avenue and Balboa Park. However, rail service reverted back to buses three days later because of issues with overhead wires coupled with a COVID-19 infection among control personnel.
Between December 2020 and February 2022, rail operations gradually resumed: starting January 23, 2021, the T Third Street line utilized the subway between Ferry Portal and Embarcadero; full service for N, KT (K and L interlined), and S lines resumed by May 15; the M line restarted on August 14; and J Church returned to underground operation on February 19, 2022 after functioning exclusively on surface routes since December 2020. The L Taraval line continued bus substitution until September 28, 2024 due to ongoing construction activities.
BART maintains frequent service intervals here as four out of its five rapid transit lines share these two tracks.
The Central Subway, completed in November 2022, links to the Market Street subway via an underground pedestrian passage connecting Powell Street station with Union Square/Market Street station. In January 2023, T line service was redirected from the Market Street subway into the Central Subway corridor, providing a direct one-seat ride from Chinatown to Visitacion Valley.
Stations in the Market Street subway
The tunnel contains seven stations: four are served by BART trains, while all seven accommodate Muni Metro lines that previously operated along Market Street’s surface. The J Church and N Judah lines exit through the Duboce portal, bypassing Castro Street and Church Street stations; J trains stop at street-level platforms on Church Street.
Stations listed from northeast to southwest: