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Conceptualizing a Central Subway Extension

In 1989, San Francisco voters approved the Four Corridor Plan (PDF), a long-range plan to build high-capacity transit lines on Geary, Van Ness, Stockton/Columbus, and the Third Street/Bayshore corridor.

The Third Street Light Rail Project covers the latter two corridors, mostly.

Phase 1 of the T-Third Street line was the surface segment opened in 2007. The route along the Embarcadero and through the Market Street Subway as an extension of the K is a temporary arrangement.

Phase 2 is the Central Subway now under construction. When finished T-Line trains will continue up Fourth Street, entering a subway near Moscone Center, crossing under Powell Station on the way to Chinatown.

Chinatown is the northernmost station and as far as voters approved funding for. The tunnels already continue to North Beach, where the tunnel boring machines were removed, and work has quietly been getting underway for a Phase 3.

Phase 3 will add a Station in North Beach and one or two in Fisherman’s Wharf depending on the route.

A conceptual study (PDF) released last year was one of the first steps. The point of this study was to identify potentially feasible routes which will be the basis of further planning.

There are four basic route options, with variations for subway and surface/subway combinations and track configurations. All options begin with that subway station in North Beach.

• Option 1 continues the subway along Columbus to where it meets Beach Street at the triangle-shaped Conrad Square Park.
• Option 2A follows Powell Street to Beach Street (where the Muni bus yard sits currently)
• Option 2B continues one station further to Columbus & Beach (Conrad Square where Option 1 ends as well)
• Option 3 is a one-way loop with the same two stops in Fisherman’s Wharf.

Any subway extension will have to dive to make a 60’ dive after North Beach in order to cross under a sewer main. The much cheeper and easier is to have the trains come to the surface for the final stop, but that impacts speed, safety, and reliability.

The study didn’t make a specific recommendation, or rule out any options. The study did score the 14 combinations of surface and subway routes on a range of factors including costs, risks, speed, and reliability. Though Option 1, running exclusively in a subway under columbus scored best.

This study is just one in a series which will refine the options and cost estimates, and eventually put together a funding package and a detailed project timeline. The next decision point comes in May when the SFMTA needs to decide if they wish to extend the lease on the Pagoda Palace worksite in North Beach where those tunnel boring machines were removed.