Since the Caltrain/HSR blended system came up at GNC, I thought you might be interested in the feasibility analysis conducted by Caltrain this spring which allowed the HSR board to approve a blended approach. The consultants presented some of this material at the Dec 2011 community meeting. Here is the final March 2012 report.http://www.caltrain.com/
Assets/Caltrain+Modernization+ Program/Documents/Final- Caltrain-California+HSR+ Blended+Operations+Analysis.
The analysis showed that the blended approach was feasible provided several key assumptions were met, including TWO dedicated high speed rail tracks at Diridon and various new overtake segments. From page 19
San Jose Diridon Station
In the vicinity of the San Jose Diridon station, the design includes dedicated high speed tracks and station platforms. The dedicated two-track HSR alignment continues northward and merges into middle of the Caltrain mainline north of CP De La Cruz. It was assumed in the model that the two Caltrain tracks were spread apart with the HSR tracks accessing the existing Corridor alignment between the Caltrain tracks. The HSR tracks were assumed to merge into the Caltrain tracks using #32.7 turnout geometry, supporting 80 MPH diverging movements for HSR.
The TWO dedicated high speed rail tracks can be above ground, below ground, or at grade.
If above ground, the double deck aerial structure meets the requirement and would descend to ground level in Santa Clara.
If underground, the requirements are met...the train sets would need to surface past De La Cruz.
If at grade, the two additional platforms would need to be constructed at Diridon---widening the right of way to the east: requiring removal/relocation of electric substation, the existing brick buildings, and some of the land needed for baseball stadium. The right of way would have to be widened past OSH and over Hwy 280. The bends of the S-curve through North Willow Glen/Gardner would need at least partial reconstruction. A "blended" approach would probably allow Auzerais and Virginia Street to remain "at grade" crossings. A "blended" approach would require widening of the ROW at The Alameda since the HSR trainsets are very long and the platforms will extend over The Alameda when they stop. This would require a longer section of car under crossing, possibly extending to the Arena and past Stockton Avenue. A preliminary calculation a couple of years ago showed it might be hard to come back to at grade by Stockton Avenue as currently aligned. The Stockton Av alignment might have to be moved to the west (Through Whole Foods). The ROW would be wider through at least Julian street, potentially either taking Arena land or the server farms to the west of the ROW. Eventually the tracks can come together and "blend."
In order to eliminate the problems associated with the wider at grade ROW, the consultant could be asked for the feasibility of a blended system without the two dedicated HSR platforms at Diridon. To me, it doesn't look possible after examining the strings in the above report. The curve straightening in North Willow Glen would still be required.