The line operates mostly on Fillmore Street and 16th Street, using Hermann and Church Streets to transition between the two. A short segment near the northern end of the line runs one block west of Fillmore on Steiner. The outbound terminal is listed as Fillmore and Bay, although inbound buses continue further north, stopping at Jefferson before turning around and doubling back before running south to Mission Bay.
Fillmore Counterbalance section of the route, where electric trolleys operated via cable haulage, early 1900s
Streetcar service on the line started in July 1895, running from 16th and Folsom Streets to Fillmore and Broadway. Running further north required a means to traverse the steep 24.54% grade of Pacific Heights. Thus the line was uniquely equipped with a funicular-style mechanism between Broadway and Green whereby a descending streetcar would provide counterweight for an ascending car by coupling both to a shared cable. The Fillmore Street counterbalance opened the following month. This section limited frequency and scheduling on the entire route as it required two passing cars to meet up at the appropriate points for the mechanism to operate.
The funicular segment was replaced with shuttle buses in 1941, diverting from the route a block to the west to avoid the steep grade. Streetcar service along the whole line ended in the early hours of August1, 1948. The route was changed slightly to use Hermann Street rather than Duboce Avenue to jog between Church Street and Fillmore Street. After a few months of temporary motor coach service while work to modify the overhead wires took place, the route was converted to trolleybuses on January 16, 1949.
By 2016, very few further changes had occurred to the routing since the first streetcars ran a century earlier. The eastern/southern terminus of the line was moved from the Dogpatch to Mission Bay in January 2021.
Turning around at the line's outbound end at Fillmore and Marina Boulevard
↑"Short Range Transit Plan"(PDF). San Francisco Municipal Transportation Agency. December 3, 2019. Archived(PDF) from the original on June 5, 2020. Retrieved December 27, 2021.
12Foster, S. L. (June 1896). "Ascending Grades by Electric Force". Street Railway Journal. XII. New York: The Street Railway Publishing Company: 371–373.
↑McKane, John; Perles, Anthony (1982). Inside Muni: The Properties and Operations of the Municipal Railway of San Francisco. Glendale, CA (US): Interurban Press. p.222. ISBN0-916374-49-1.