Twin Peaks Tunnel

The Twin Peaks Tunnel is a 2.27-mile (3.65 km)-long light rail/streetcar tunnel in San Francisco, California. The tunnel runs under the Twin Peaks and is used by the K Ingleside/T Third Street, L Taraval, M Ocean View, and S Castro Shuttle lines of the Muni Metro system.

History and background

The tunnel was opened on February 3, 1918. The eastern entrance to the tunnel is located near the intersection of Market and Castro streets in the Castro neighborhood, and the western entrance is located at West Portal Avenue and Ulloa Street in the West Portal neighborhood.

Seen here in 1919 is the original archway of the West Portal of the Twin Peaks Tunnel.

The service through the tunnel has evolved from streetcars into light rail, and while there are longer light-rail tunnels elsewhere (such as Portland's Robertson Tunnel), the Twin Peaks Tunnel remains one of the world's longest streetcar or light-rail tunnels. There are two stations along the tunnel, Forest Hill near the western end, and the now disused Eureka station near the eastern end.

The East Portal of the Twin Peaks Tunnel in 1935 with a K Line streetcar at Market and Castro.

When the Muni Metro system and Market Street Subway were built, they were connected to the Twin Peaks Tunnel to be used by the K Ingleside, L Taraval and M Ocean View lines. The Eureka station was closed, and the Metro lines stop at the nearby Castro Street Station instead.The original eastern entrance to the tunnel in the middle of Market Street at Castro was removed and new entrances were placed on the sides of the street further up the block, though no Metro or streetcar lines use them in regular service (they were used during construction of the Market Street subway and are occasionally used in non-revenue service such as rerouting trains around construction projects). Instead, trains continue directly from the Market Street Subway into the tunnel without going above ground.

Forest Hill and Eureka stations were originally constructed with low platforms, as streetcars of that era had steps to load passengers from street level. However, the six new Market Street Subway stations were built with high-level platforms for speedier level boarding onto the new Boeing LRVs. West Portal station, which was originally a surface stop outside of the tunnel's western entrance, was rebuilt as a high-platform station located just inside of the entrance. With Eureka station permanently closed, Forest Hill was left as the only low-platform station on the Muni Metro subway. Muni soon modified the station with high-level platforms, with completion in 1985.

The new, larger West Portal station designed to work with Boeing light rail trains was dedicated on April of 1979.