The Market Street Railway opened its 22 Fillmore streetcar line in 1895; it jogged from Church Street to Fillmore Street on a short section of Duboce Avenue. On October 21, 1928, the San Francisco Municipal Railway N Judah streetcar line opened. It ran on Duboce Avenue between Market Street and the Sunset Tunnel, and shared track and overhead wires with the 22 for one block. Muni took over the ex-Market Street Railway system in September 1944. Muni converted a number of streetcar lines, including the 22, to trolleybus on July 31, 1948; it was rerouted via Hermann Street one block to the north to avoid conflicts between the overhead wires for trolleybuses and streetcars. Beginning in the late 1960s, construction of the Market Street subway required diversions of Muni's five remaining streetcar lines, which ran on Market Street. The largest diversion routed K, L, and M cars from the Twin Peaks Tunnel onto new tracks on 17th Avenue, joining the J Church on Church Street, and continuing past Market Street on new tracks to join the N Judah tracks on Duboce. An inbound concrete boarding platform was built on Church Street at Duboce Avenue; outbound cars stopped further south on Church Street at Market Street. Streetcars on the J, K, L, and M lines were routed onto the diversion route on December 2, 1972, though only outbound cars used the diversion north of Market Street until 1973. The new Duboce Portal was constructed on Duboce Avenue east of Church, parallel to the operating surface streetcar line. N Judah trains began using the new portal on weekdays on February 18, 1980 - the first Muni Metro service. On December 17, 1980, the K, L, and M lines began Muni Metro service on weekdays. J Church trains began using the new portal on June 17, 1981. Finally, on September 19, 1982, weekend service was replaced by buses, leaving only the inbound J Church stopping on Church at Duboce. This station will be the northern terminus for the J Church service starting in August 2020, when Muni service is projected to return after the COVID-19 pandemic. Accessible sections of high-level platforms were later built east of Church Street, near the entrance to the portal. These accessible platforms serve both lines; because the J Church stop at Market Street is not accessible, outbound J Church trains serve Duboce and Church if required by a passenger. Since the diversion in 1972, Duboce Avenue between Church Street and Market Street is not open to automobiles. A sidewalk and bike lanes run along the south side of the portal, and a 2-track Muni yard sits on the north side. A Muni operator facility is located next to the yard. Under Muni stop naming conventions, the stop is known as Duboce and Church for the N Judah, and Church and Duboce for the J Church. Failures of the interlocking between the J and N lines can cause significant cascading delays in the Market Street subway. Eight such failures occurred between 2017 and early 2019. As part of August 2020 changes to Muni Metro, the J will become an all-surface line to avoid this issue. The J will initially terminate at the inbound platform on Church Street at Market Street, providing an accessible transfer between the J and subway trains. A mini-high platform will be constructed on the inbound platform at Church and Duboce, and an outbound mini-high platform will be built on Church Street south of Market Street, allowing the J to be re-extended slightly to Duboce Street in October 2020.
