Why are fast train fast, If there were no constraints, how would the fastest train look.?

Question

Why are fast train fast, If there were no constraints, how would the fastest train look.?

Answer 1

Trains are fast because they put lots and lots of power on a fairly lightweight train, and then make it somewhat aerodynamic.  

With no constraints, the fastest train would look like a bunch of locomotives, if you didn't have to deal with silly stuff like where to seat the passengers.  

It would also look like a teardrop in shape, because that's the most aerodynamically efficient.  If you didn't have to deal with silly things like wheels, center of gravity, doors and bidirectional operation.

Answer 2

french train just took over as the fastest  seeing is believing.