N Judah  The N Judah is a Muni Metro light rail line in San Francisco, California, so named as it runs along Judah Street for much of its length, named after railroad engineer Theodore Judah. It links downtown San Francisco to the Cole Valley and Sunset neighborhoods. It is the busiest line in the Muni Metro system, serving an average of 41,439 weekday passengers in 2013. It was one of San Francisco's streetcar lines, beginning operation in 1928, and was partially converted to modern light-rail operation with the opening of the Muni Metro system in 1980. While many streetcar lines were converted to bus lines after World War II, the N Judah remained a streetcar line due to its use of the Sunset Tunnel. The line runs from the Caltrain depot in the Mission Bay district to Ocean Beach and the Great Highway in the Sunset District. From the Caltrain depot at Fourth and King Streets, it runs along King Street and the Embarcadero, passing by Oracle Park. It then enters the Market Street subway, which it shares with the five other Muni Metro lines. It exits the tunnel at Church Street and, after a brief stretch along Duboce Avenue to Duboce Park, enters the older Sunset Tunnel. This tunnel serves to avoid a hill and contains no underground stations. From the western end of the tunnel, the route goes along Carl Street, past UCSF-Parnassus Campus, on Irving Street, until it turns onto 9th Avenue for one block and reaches Judah Street, which the N runs on for the rest of its route. On Judah between 9th Avenue and 19th Avenue the N runs on a right-of-way that is slightly raised above the surrounding street. There is a loop in the intersection at Judah, La Playa and Great Highway that the N uses to turn around. As with all Muni lines, service begins around 5 a.m. on weekdays, 6 a.m. on Saturdays, and 8 a.m. on Sundays and holidays. It operates at high frequencies, mainly between 7 and 12 minutes, and mostly utilizes two-car () trains during Muni Metro hours of operation. Service is provided by overnight Owl buses on the N Owl route during the hours that rail service is not running. On weekends, N Judah Bus service runs from 5am until the start of rail service. The bus lines largely follow the rail line, but use surface streets to parallel sections where the rail line has dedicated rights-of-way. On January 10, 1998, Muni opened the Muni Metro Extension to 4th and King/Caltrain.