The T Third Street is a Muni Metro light rail line in San Francisco, California. It runs along the east side of San Francisco from to , traveling in the median of Third Street for most of its length before entering the Central Subway as it approaches downtown. The line serves 22 stations, all of which are accessible. Most of the surface portion of the line runs in dedicated median lanes, though two portions operate in mixed traffic. Construction of the line was proposed in the late 1980s as plans for the redevelopment of the Mission Bay neighborhood were established. Construction took place in the mid-2000s. Limited service began in January 2007, with full service beginning in April of the same year. The line was rerouted north of to travel through the Central Subway to Chinatown on January 7, 2023. It was the first line added to the Muni Metro system since the N Judah in 1928. Operations Route The T Third Street's northern terminus is Chinatown station inside the Central Subway. Trains operate south below Stockton Street to Union Square/Market Street station, which offers a connection to Powell Street station as the line does not enter the Market Street subway. The line then tunnels underneath 4th Street to serve Yerba Buena/Moscone station in the SoMA district before surfacing south of the Interstate 80 bypass, where it serves a stop at Brannan Street. The T then crosses the existing N tracks at 4th and King and continues south to 3rd Street. Additional short turn service between Chinatown and Mission Bay Loop will be later added. The line runs south through the Mission Bay neighborhood in a dedicated median, passing the Mission Bay Loop between 18th and 19th Streets, which is used to allow trains to turn around at Mission Bay or to hold special trains to serve events at Chase Center. The line continues south through Dogpatch and across Islais Creek into the Bayview and Hunters Point neighborhoods. It runs in mixed traffic for from Kirkwood Avenue to Shafter Avenue, then returns to dedicated lanes. A wye, occasionally used for short turning trains, is located at Armstrong Avenue. The line crosses the U.S. Route 101 freeway, where Third Street becomes Bayshore Boulevard, and continues south in the median. The southern terminus of the line is at Sunnydale station in the Visitacion Valley neighborhood. Service The T Third operates seven days