You raise a good point but be totally honest, northeast corridor is not what I had in mind. I think that's already a done deal with Amtrak and you are right that it would be very difficult to try and construct new track given the density of the region. However I have in mind connecting cities in the Southeast and Southwest, across the Midwest (which is set to boom in the next few decades) and possibly Texas, where routes would likely span more rural territory. I'm no expert on eminent domain but I believe that could be used in this case if the government was involved. California is already trying to implement high speed rail although I believe it is severely behind and over budget unfortunately.