All I can tell you is that in most jurisdictions around the world that is precisely what has happened. Where there is high-speed rail for a relatively short period of time--and I'm talking about three- to four-hour trips, not twelve hour trips--the passengers have shifted to train rather than air for two reasons: one, the convenience; and, two, generally speaking, the rail systems have been able to offer more competitive pricing because they have much higher volumes in the same unit.
