It is an advantage that HSR uses Caltrain track to get to SF. It would be super expensive to build a separate high speed line, and it wouldn't be worth the time savings. Caltrain should spend money grade separating the whole line, adding passing lines where possible, and increasing the speed to 125mph or 150mph since it would be good for Caltrain service. At 125mph, HSR (250mph) would save 10 minutes, and 150mph would save 6 minutes.