I'm skeptical about HSR... I think if it became popular, it would be too tempting of a target for terrorism. The air network is very flexible and resilient. 9/11 was absolutely awful, but did it affect the air system? No. Air travel was shut down for three(?) days while we all caught our collective breath and tried to figure out what was going on, but air travel itself was really unaffected. Even if you wiped a major airport like JFK completely off the map, the system would deal. Say there were a HSR line from Boston to Miami that replaced a lot of the air travel that currently takes place up and down the East coast: Boston, NYC, Philly, Baltimore/DC, Charlotte, Atlanta, Orlando, Tampa, Miami. You simply cannot protect 1200 miles of track; take out any one piece, and travel will be suspended for weeks or months for expensive repairs.