Between 18th and 20th Street, the line cuts through Dolores Park in a private right-of-way featuring a 9% grade, the steepest section of the Muni Metro system.

At the end of the line, the J loops around the Metro yard at San Jose and Geneva, alongside Balboa Park station.

[6] As part of the creation of the Muni Metro system, it was partially converted to modern light rail operation in 1981 — the last line to do so.

[10] In 1990–91, the tracks were extended to the Balboa Park BART station and the Metro Center (Muni light-rail maintenance and operations base), giving J-line cars a much shorter connection to the yard than previously.

The extension opened on August 31, 1991, but the 2.3-mile (3.7 km) new section was initially used only by light rail cars starting or ending their runs;[11] all-day J-line service was not extended along the new tracks until June 19, 1993.

[5] This extension of the J-line to the Metro Center now also provides vintage F Market cars a connection to the adjacent Cameron Beach Yard, where they are stored when not in service.

The 19th Avenue Platform & Trackway Improvement Project originally included pocket tracks to allow J Church trains to continue past Balboa Park with service to Stonestown.

[7] In March 2014, Muni released details of the proposed implementation of their Transit Effectiveness Project (later rebranded MuniForward), which included a variety of changes for the J Church line intended to improve reliability and decrease travel times.

The proposed changes included the removal of two stops (Liberty and Church and 30th Street), minor relocations of several other stops, construction of boarding islands and transit bulbs, and transit-only lanes on three blocks of Church Street, plus an increase in frequency from 9.5-minute headways to 8-minute headways during the morning peak.

[22] Rail service was again replaced with buses on August 25 due to issues with malfunctioning overhead wire splices and the need to quarantine control center staff after a COVID-19 case.