Urban development and CA High Speed Rail -> further cuts to I-280 San Francisco?

[sparker]

From what I have read, the underground portion of the BART line isn't a single track but rather a single tunnel with two levels, each containing a single track.  Downtown San Jose businesses favored this type of tunnel because it eliminates the need to use the cut-and-cover method of construction.  The tunnel would be bored with minimal disruption at the surface.

Now that makes more sense than the configuration that I originally heard (thanks for the partial info, Murky News! ) and talked about.  I suppose with the advances in boring equipment any arrangement, even such an over/under configuration, has become possible.  Even the upper level will have to be quite deep; much of downtown's been dotted with projects to upgrade utilities just below the surface over the last few years; BART will certainly have to duck under those facilities.  It'll be interesting to see how they deal with both Coyote Creek and the Guadalupe River en route to, respectively, downtown/SJSU and Santa Clara; their previous encounter with a significant floodplain on this line was with Alameda Creek in Union City, which they crossed on a viaduct.