Take a 375 mph train. The same 3,000 miles is about 8 hours. Add between 15 minutes and a half hour at each end (I've never had more than a half hour wait to get on an on time Amtrak - including checking in when I needed to.) 8.5 to 9 hours. Two to two and a half hours time difference. But given how less frazzling the difference was I'd say most people would choose the train if prices were comparable. And no there is no train that can do that a present. But no one thinks it impossible either.
What about a 4,000 mile journey. Well the difference would be bigger but as I said still tolerable in that you are not suddenly cutting people off from each other reversing the world getting smaller. The difference there is between a seven hour trip and an eleven hour trip. Still would pay in comfort what it costs in time.
Jordan: here is the thing, There is no technical solution to airplane emissions if people continue to fly the same number of miles. Leave aside all the inefficiencies in hydrogen production: for something like air travel they would be worth it if they would work. The problem is that if we flew an airplane on hydrogen the added water would make up for the carbon reduction. In the stratosphere or even upper troposphere, water vapor is a forcing not a feedback - unlike on the ground. So we either replace a lot of plane travel with ground travel or just cut traveling a lot. And I really think people traveling longer distances is one of the good things capitalism has done; it is something I do NOT want to lose.
Michael: I don't have the figures in front of me. But when a train starts traveling at 300 mph it does so very inefficiently. So really fast trains are comparable in efficiency to planes - less efficient in some cases, more in others - depends on the plane and the train. A fast moving train does not give you a good passenger mile per gallon figure. But as I said it can run on electricity, and we have lots of potential for renewable electricity. Not as cheap as coal of course, but maybe cheaper than natural gas, and certainly cheaper than oil planes presently run on. The hard part about high speed trains is the capital cost. High speed track is amazingly expensive. And the trains themselves are not cheap. If we can build the trains running them on expensive renewable electricity won't be a problem. The energy premium for speed will be no worse than with airplanes. Whether we can find a way to get the capital cost down is an interesting question.
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