In 1972 , Muni began planning an long-proposed extension of the J Church line along San Jose Avenue ( a section of which was built along the former Ocean View Branch through the Bernal Cut ) to Balboa Park . The extension was intended to provide transit service to the Outer Mission , allow J Church and N Judah trains to access the carhouses via San Jose Avenue rather than a roundabout route via the K Ingleside line , and allow future through-routing of the J and M lines . Construction on the extension began in January 1989 , but was delayed by the earthquake later that year . On August 31 , 1991 , J and N streetcars began using the extension to access the yards , thus providing revenue J service to Balboa at limited hours . Full-time revenue service began June 19 , 1993
the earthquake later that year
1989 Loma Prieta earthquake
Balboa Park station