The Sunset Tunnel, originally known as the Duboce Tunnel, is a -long light rail/streetcar tunnel in San Francisco, California. The tunnel runs under the steep hill adjacent to Buena Vista Park and is used exclusively by the N Judah Muni Metro line. The eastern entrance is located at Duboce and Noe streets on the south side of Duboce Park in the Duboce Triangle neighborhood, and the western portal is located in Richard Gamble Memorial Park near the intersection of Carl and Cole streets in the Cole Valley neighborhood. History Initial proposals Bion J. Arnold proposed a Mission–Sunset Tunnel in his Report on the Improvement and Development of the Transportation Facilities of San Francisco of March 1913. In Arnold's scheme, the Mission–Sunset Tunnel would start at Eureka Valley station, which was proposed as the transfer station for passengers needing service through the Twin Peaks Tunnel. The Mission–Sunset Tunnel would serve as a feeder bringing rail, automobile, and pedestrian traffic from the Panhandle region to the planned Market Street Subway. It would also improve service to the Sunset District from the Mission and other areas south of Market, as existing routes were circuitous or limited. Arnold's plan called for a two-level tunnel, with a road and pedestrian tunnel similar in cross-section to the Stockton Street Tunnel above a two-track rail tunnel. Depending on the planned alignment and portal locations, the length of the Mission–Sunset Tunnel proposed by Arnold would have been . However, further work on a tunnel to the Sunset District was postponed in favor of completing the Twin Peaks Tunnel, which opened to revenue service in June 1918. Soon afterwards, in July 1918, a Sunset Tunnel alignment matching the as-completed route along Duboce Avenue was proposed. After the San Francisco Board of Supervisors appropriated funds for a tunnel into the Sunset in September 1921, City Engineer M.M. O'Shaughnessy was tasked with recommending a final alignment. He considered four routes, of which two relied on surface routes (one of these would run north from Laguna Honda), one was based on Arnold's 1913 proposed routing from the Eureka Valley station, and one matched the proposed Duboce route from 1918; of these four, O'Shaughnessy preferred the Duboce route as noted in a November 1921 Board meeting. The Board approved the Duboce alignment in a resolution passed on May 31, 1922 which also established the special assessment district. The route was opposed by several