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.