There is a very real problem with beefing up rail on the Altamont corridor: turf. I don't think you have to be of a conspiratorial mindset to entertain the possibility that the CCJPA and BART will not look kindly on any project that has the potential to drain their rider-shed.
Makes you wonder the real reasons for what just happened to ACE Forward.
If Altamont were built out in a way that eventually enables 220 mph Bay to Valley service, it would blow the doors off the Capitol Corridor on SF-Sac and SJ-Sac. A realistic alignment with realistic speeds would enable a train to leave SF Transbay and pass through Tracy just 35 minutes later. This is the plot that you are never supposed to see:
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