BART wants to build a second transbay tube by 2027 to ease overcrowding in the Bay Area's already stressed rail system, but its expansion plans may not stop there.

According to the San Francisco Examiner, the agency is also looking at a possible extension to the west along Geary Boulevard.

BART General Manager Bob Powers told the Examiner last week that the agency will explore running a line down Geary as part of its upcoming study of a second bay rail crossing.

That's encouraging news for the approximately 114,000 Richmond District neighbors who rely on Muni buses to commute to the downtown every day. Certainly, many would happily trade their Muni route for a direct rail connection, especially those who have to hop on a bus before taking BART to their jobs in the East Bay or South Bay.

State Sen. Scott Wiener told the Examiner, "I would love to see subway service, whether it’s BART or Muni, on the West Side of San Francisco." Weiner would also love to see such an expansion accompanied by new high-density housing along its corridor.

Rail service between the Richmond and downtown is not exactly a revolutionary idea. In fact, for nearly a half-century, a streetcar line did run on Geary, from "Market Street to the beach," as a July 1956 San Francisco Chronicle article notes.

So what happened to the streetcars that served the Richmond, on what was then the busiest streetcar line in the city?

They were casualties of the rise of the automobile. In 1956, San Francisco planners decided that the two-lane-wide Geary needed to be widened into a six-lane speedway with two additional lanes for curbside parking. To make room for the extra lanes they shaved about seven feet off the width of the sidewalks.

There was no room left for the streetcars.

Then-Assistant City Engineer Clifford J. Geertz said at the time the changes "will result in a broad, smooth roadway along Geary between Gough Street and Masonic Avenue making future streetcar service to the Richmond District impossible," the Chronicle reported.

Transit planners figured bus routes could compensate for the loss of rail.

The streetcar rails were ripped out of the pavement in 1956-58. But by 1962, BART planners were already mapping out possible future extensions of the new transit system even though it wouldn't be ready to move trains for years.

One such extension was a line to Marin County via a Golden Gate Bridge retrofitted to accept BART trains on a separate deck. The extension, presumably a subway, would follow Geary Boulevard before taking an hard right to the Golden Gate Bridge approach at Park Presidio.

RELATED: Marin County could have had BART, but backroom politics got in the way

The Marin line didn't pan out — the Golden Gate Bridge District didn't want BART on the bridge and a tube under the Golden Gate was deemed too expensive. No Marin line meant no Richmond District line.

Even if it is determined to be feasible, BART-to-the-Richmond would likely cost billions of dollars and take many years to build, and it stands to be less of a priority than a second transbay tube.

All of which would indicate it has a long way to go before becoming a reality.

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Mike Moffitt is an SFGATE Digital Reporter. Email: moffitt@sfgate.com. Twitter: @Mike_at_SFGate.