Travels within the East Bay from Twitter routed along most densely geotagged corridors
The main implication, as far as I am concerned, being that because of its traditional focus on downtown commuters, BART does not do a very good job of serving the most promising corridor in Berkeley and North Oakland, which would run approximately under San Pablo, University, the UC Berkeley campus, Telegraph, a jog over to College, Broadway, 40th/Linda, Grand, and some sort of route from the Grand-Lake district crossing Park Boulevard to near 14th and Foothill. Some of this, especially at the south end, would be difficult because of topography, but it could probably be approximated. Needless to say, if this were to be constructed, it would have to be pretty much entirely in subway to avoid tearing down the neighborhoods it would intend to serve.
(32060 trips routed through 10000 geotags. Data from Twitter streaming API. Base map from OpenStreetMap, CC-BY-SA. Peninsula section at bottom left excluded.)