Muni Metro is a semi-metro system[8][9] (form of light rail) serving San Francisco, California, United States.

Operated by the San Francisco Municipal Railway (Muni), a part of the San Francisco Municipal Transportation Agency (SFMTA), Muni's light rail lines[A] saw an average of 87,000 boardings per day as of the third quarter of 2024 and a total of 24,324,600 boardings in 2023, making it the sixth-busiest light rail system in the United States.

Five services – J Church, K Ingleside, L Taraval, M Ocean View, and N Judah run on separate surface alignments and merge into a single east–west tunnel, the Market Street subway.

[12][13] The system slowly expanded, opening the Twin Peaks Tunnel in 1917,[14] allowing streetcars to run to the southwestern quadrant of the city.

[16] In the 1940s and 1950s, as in many North American cities, public transit in San Francisco was consolidated under the aegis of a single municipal corporation, which then began phasing out much of the streetcar network in favor of buses.

Original plans for the BART system drawn up in the 1950s envisioned a double-decked subway tunnel under Market Street (known as the Market Street subway) in downtown San Francisco; the lower deck would be dedicated to express trains, while the upper would be served by local trains whose routes would spread south and west through the city.

[23] At the time, there were no firm plans to revive any service on the surface of Market Street or return PCCs to regular running.

[22] However, tracks were rehabilitated for the 1983 Historic Trolley Festival,[23] and the inauguration of the F line, served by heritage streetcars, followed in 1995.

[24] In the mid- to late-1990s, San Francisco grew more prosperous and its population expanded with the advent of the dot-com boom, and the Metro system began to feel the strain of increased commuter demand.

Newer, larger Breda cars were ordered, an extension of the system towards South Beach — where many of the new dot-coms were headquartered — was built, and the underground section was switched to Automatic Train Operation (ATO).

[26][27] In fact, the new trains were so heavy (10,000 pounds (4,500 kg) more than the Boeing LRVs they replaced) that some homeowners, claiming that the exceptional weight of the Breda cars damaged their foundations, sued the city of San Francisco.

[31][32] The ATC system was plagued by numerous glitches when first implemented, initially causing significantly more harm than good.

Common occurrences included sending trains down the wrong tracks, and, more often, inappropriately applying emergency braking.

[34] After initial problems with the ATC were fixed, substantial upgrades to the entire Muni transit systems have gone a long way towards resolving persistent crowding and scheduling issues.

[38] The line ran into initial problems with breakdowns, bottlenecks, and power failures, creating massive delays.

Muni estimates that the Central Subway section of the T Third Street line will carry roughly 35,100 riders per day by 2030.

[46] The SFMTA reopened rail service on August 22, 2020,[47] but returned to bus substitution three days later, citing malfunctioning overhead wire splices and the need to quarantine control center staff after a COVID-19 case.

Kirschbaum said the agency was reconsidering its approach to maintenance after the botched attempt to reopen in August, and that it might take 5 to 8 years to fully address the system's vulnerabilities.

City supervisors harshly criticized the mistake, which SFMTA director Jeffrey Tumlin blamed on a "culture of fear" he was working to correct since becoming the agency's leader in 2019.

The L remained served by buses due to a multi-year reconstruction on the surface section of the line until it resumed train service on September 28, 2024.

[62] Starting in 2017, the SFMTA, in collaboration with other city agencies, began its ConnectSF process to plan its vision for future transit expansions that would follow its then under construction projects such as Van Ness BRT and the Central Subway.

[63] The final report on transit from the ConnectSF program was released in 2021 and identified two major corridors for Muni Metro expansion: a subway line along the Geary Boulevard and 19th Avenue corridor connecting to Daly City, and the extension of the Central Subway to Fisherman's Wharf that had already undergone preliminary analysis.

A select number of stops, typically located near major intersections, are equipped with ramps or lifts, for people with disabilities.

[91] Two Boeing cars were preserved for potential donation to the San Francisco Railway Museum, but have since been scrapped;[95] five were sold to the Greater Manchester Passenger Transport Authority for the modest price of US$200 (equivalent to $338.8 in 2023) to US$500 (equivalent to $846.99 in 2023) each; one was acquired by the Oregon Electric Railway Historical Society in 2001, but the Society declined to take any more Boeing cars after experiencing several breakdowns.

[105][106] With the Breda cars growing increasingly unreliable and the system expanding with the construction of the Central Subway, Muni requested bids for a new generation of light rail vehicles.

Muni prequalified CAF, Kawasaki and Siemens to bid on the request while Breda was disqualified based on a ranking of potential bidders.

[107][101] A grant of $41 million from the California Transportation Agency awarded on July 2, 2015, allowed Muni to purchase 40 additional Siemens light rail vehicles.

To participate in the program, a qualified senior must have or obtain a Clipper card and submit an application either online or by mail.

[118] Subway stations have controlled entries via faregates, and passengers usually purchase or show Muni staff a ticket in order to enter the platform area.

Faregates closest to an unmanned Muni staff booth open automatically if a passenger has a valid pass or transfer that cannot be scanned.