Revealed a few months ago during the scoping process, CHSRA considered Downtown diagonal options to straighten the corridor and to avoid the area south of 280 and west of 87. That diagonal alignment included an elevated and an underground option.
Like all other NIMBYs further up on the peninsula, neighborhoods' reaction is to prefer the underground option. What the HSR planners found is that the underground option is nearly unbuildable with high groundwater table and would cost 6 times the base cost. The proposed underground option would be more than 100 feet deep to go below a river, light rail, and a possible BART subway alignment and would have a concourse and at least 4 tracks.
HSR planners recommend to put the high speed rail station on top of the existing Caltrain station, and further review two alignments that would connect the Diridon station with Tamien station. One of which would stay on the current Caltrain alignment.
Many delusionals still believe that putting train underground is the best.
"The community will ask why this is so difficult when BART is already underground "... the community will think the board only wants the cheapest, and not the best, alternatives," Dresden told the board.
The fact is that BART is not underground. BART is in fact not anywhere near there at all. VTA does have a plan to build a BART subway there but has no funding for it, and the neighborhoods have yet to experience any impact resulting from the subway construction. Their demand for an underground high speed rail would require it to go under the BART white elephant, which without a doubt adds cost and more importantly, reduces construction feasibility. If the neighborhood folks aren't so naive, perhaps they could have demanded better alternatives for both high speed rail and BART (like Altamont HSR) before things got to where they are now.