BART is officially studying the possibility of constructing a second Transbay Tube which would take BART service through Alameda, into SoMa, and potentially out to the western part of the city that's currently only served by sad bus lines like the 38. As StreetsBlog reports, though completion of the project would be decades in the future, BART recently informed a committee of SF Supervisors that it plans to launch a full study of the costs, logistics, and benefits of the project which could, potentially, double BART's capacity for serving Bay Area commuters in the future.

The project would, theoretically, split in half the number of commuters who currently have to come through Embarcadero Station, shuttling people directly to and from jobs in SoMa and the southern half of the city, as well as providing a vital new transit link to the Richmond and Sunset Districts — parts of town that remain under-developed and not particularly dense because of their lack of transit access.

Under a visioning project that started a couple years back, ideas have been floated like extending BART up Van Ness Avenue to the Presidio, adding an in-fill station at Mission and 30th Street on the existing BART line, and creating a turnback station at Glen Park in order to run more trains through the busiest parts of the line.

Here are the current particulars:

Under BART’s preliminary vision, the Alameda-SoMa tube would extend underneath the existing BART and Muni tunnels that run under Market, crossing somewhere between Powell and Montgomery Stations, Smith said. The route would also cross beneath the Central Subway tunnel, which has been dug underneath Powell Station and Union Square.

From there, BART could run along the Geary corridor towards SF’s western neighborhoods, finally bringing rail service to the Richmond. Smith said BART will look at alternatives like a spur to the Outer Richmond, with a branch turning south near Masonic Avenue, towards the east end of Golden Gate Park and the University of California at San Francisco’s Parnassus Campus. From there, the route would run south near 19th Avenue, connecting to BART’s Daly City and Colma stations.

As Ellen Smith, BART’s acting manager for strategic and policy planning, told the Supervisors, BART "was planned in the 1960s, when there were only 3.6 million people in the Bay Area." By 2040 that number is expected to top 9 million.

And it'll be 2040, or later, before any of this can get built.

Previously: New BART Vision Project Will Determine How It Might Expand Routes In 30 Years