T Third Street

Current alignment — conjoined operation with K Ingleside

Following service changes on June 30, 2007, the T Third Street and the K Ingleside lines were spliced together in the Market Street Subway tunnel,^[4] resulting in a route from Balboa Park, through downtown, to Bayshore and Sunnydale. At West Portal Station, inbound K trains heading through downtown to Third Street change their signs to the T line; at Embarcadero Station, T trains heading through downtown and outbound to the Ingleside neighborhood change signs to the K line. Each train displays its ultimate destination. This system will continue in place until the Central Subway is operational.

T Third Street train serving Church Street Station in 2013.

Leaving the Market Street Subway at Ferry Portal heading south, the T Third follows The Embarcadero south of Market Street, then veers onto King Street in front of AT&T Park until it reaches the Caltrain station terminal. This portion of the Muni Metro rail line between the Embarcadero portal and the Caltrain terminal was built in 1998 and is utilized by an extension of the N Judah, which shares track with the T to the Caltrain terminal at 4th and King. From there the T turns south on Fourth Street, crossing the bridge over Mission Creek before joining Third Street for the majority of the route's length. It passes through Mission Bay where the UCSF Mission Bay branch is located, then continues on south through the Bayview and Hunters Point neighborhoods. Once both economically impoverished parts of the City, they have slowly experienced rehabilitation and rebuilding mainly helped by the new T line. At the intersection of Third and Jamestown Avenue, the T continues to run in both directions as it crosses U.S. Highway 101 (James Lick Freeway), although only Third Street is open to auto traffic northbound; likewise, southbound auto traffic is splintered to a southbound on ramp to Highway 101 and merges with San Bruno Avenue. From there the T follows Bayshore Boulevard (changed over from Third) for two more stations until it reaches its terminus at Sunnydale Station. A section of track follows one more block until stopped short at the Daly City limits.

All stations along this line feature high platforms, eliminating the need for the raising and lowering of entrance and exit steps characteristic of other Muni Metro lines. Stations south of Fourth and King feature short platforms that accommodate only two-car trains.

The T Third also uses the Muni Metro terminology in which an inbound train goes from West Portal to Embarcadero. This also means that an outbound T Third train runs from Sunnydale and out to the western neighborhoods via downtown.^[5] This is the reverse of other lines, as those lines have their outer termini on the southwest and west sides of the city, and those trains enter the subway from the west going inbound toward downtown.

The underground section of the line was closed west of Castro station from June 25 to August 24, 2018 due to the Twin Peaks Tunnel shutdown.^[6] On August 25, 2018, at the conclusion of the shutdown, Muni began running permanently two-car trains on the K/T line (as had been used east of Castro during the shutdown).^[7]

Future route

T-Third has been built in phases. The first phase extended rail service south to Sunnydale Station. The second phase, currently under construction, is also known as the Central Subway project, and will reroute T-Third north of the 4th and King Station. The future alignment once the second phase is complete will neither share right-of-way with, nor share identities with the K Ingleside, avoiding both King Street and the congested Market Street subway. The southern segment from Sunnydale to 4th and King Street will remain as-is, operating on street-level median tracks. After 4th and King, the line will proceed to a new 4th and Brannan Station, and the line will then burrow to subsurface level at Bryant Street Portal, near where 4th passes under Interstate 80.^[8] Underground, the line will continue under Fourth Street, to Yerba Buena/Moscone Station, and then, after crossing Market Street, will turn slightly to continue under Stockton Street, continuing to Union Square/Market Station before terminating at Chinatown Station.^[8]

Central Subway construction at the south portal in December 2017. Trains will be routed here upon completion.

A proposed third phase would build an extension beyond Chinatown, including new stations at Washington Square in North Beach and Fisherman's Wharf.^[8] In preparation, the tunnels were bored past Chinatown Station, and the tunnel boring machines were extracted from the intersection of Powell and Columbus, near Washington Square.^[9][10] The SFMTA published a concept study in January 2015 on the feasibility of several options for phase 3.^[10] The report studied three main alignments: Columbus Ave, Powell St, or a loop line on Powell St, Beach St, and Columbus Ave. Both subway and surface options were studied for each alignment. The report found that the phase 3 project could improve transit trip time by at least 50% and would increase the ridership on the T Third by 55%. Project cost estimates ranged from $440 million to $1.4 billion depending on the design. In June 2018, the SFMTA started studying alternatives in detail in order to narrow down the options for a future environmental impact study.^[11]

A conceptual fourth phase has been advanced by SFMTA and transit advocates to further extend the line west of Fisherman's Wharf to the Presidio.^[12][10] However, since the Central Subway station platforms will be about 250 feet (76 m) long, enough to accommodate two-car trains, unlike the upper deck Market Street subway platforms which can accommodate four-car LRV trains, the projected ridership increase with a fourth phase Presidio extension would require the stations currently under construction to be rebuilt to three- or four-car trains.^[10]

Former route

Initially upon opening, the T Third was operated from Castro Station to Bayshore and Sunnydale. In the aftermath of the Muni Meltdown of 2007, the T Third was suspended from operating as a distinct line, in favor of being through-routed with the K Ingleside.

Diagrams of the various T Third Street routings over its history

Initial alignment           Castro Church ← │ ↕ Van Ness Civic Center Powell Montgomery Embarcadero Folsom and The Embarcadero I-80 (Bay Bridge) Brannan and The Embarcadero 2nd and King Caltrain 4th and King / Caltrain 4th Street Bridge Mission Rock UCSF/Mission Bay Mariposa 20th Street 23rd Street   Metro East Yard   Marin Street Levon Hagop Nishkian Bridge over Islais Creek Evans Hudson/Innes Kirkwood/La Salle Oakdale/Palou Revere/Shafter Williams Carroll Gilman/Paul Le Conte US 101 Caltrain Arleta Sunnydale 2007–2019 Inbound: sign change from West Portal Forest Hill Twin Peaks Eureka Valley closed Castro Church ← │ ↕ Van Ness Civic Center Powell Montgomery Embarcadero Outbound: sign change to Folsom and The Embarcadero I-80 (Bay Bridge) Brannan 2nd & King Caltrain 4th and King / Caltrain 4th Street Bridge Mission Rock UCSF/Mission Bay Mariposa 20th Street 23rd Street   Metro East Yard   Marin Street Levon Hagop Nishkian Bridge over Islais Creek Evans Hudson/Innes Kirkwood/La Salle Oakdale/Palou Revere/Shafter Williams Carroll Gilman/Paul Le Conte US 101 Caltrain Arleta Sunnydale 2019–             Provision for future extension to North Beach and the Presidio Chinatown Powell–Mason & Powell–Hyde California Street Union Square/​Market Street Powell Yerba Buena/​Moscone Central Subway I-80 4th and Brannan original routing Caltrain 4th and King / Caltrain 4th Street Bridge Mission Rock UCSF/Mission Bay Mariposa 20th Street 23rd Street   Metro East Yard   Marin Street Levon Hagop Nishkian Bridge over Islais Creek Evans Hudson/Innes Kirkwood/La Salle Oakdale/Palou Revere/Shafter Williams Carroll Gilman/Paul Le Conte US 101 Caltrain Arleta Sunnydale Notes E Embarcadero began service in 2015

Route for second phase (under construction as the Central Subway), planned route for third phase (extension to Fisherman's Wharf), and proposed routes for fourth phase (extension to the Presidio of San Francisco)

Future

Station	Neighborhood	Other Muni Metro lines	Notes
Chinatown	Chinatown		Future terminus
Union Square/Market Street	Financial District		Underground pedestrian pathway to Powell Street station
Yerba Buena/Moscone	SoMa
4th and Brannan	SoMa