This is true for many modern high-speed trains (though those tend to not be diesel trains...), but those are only a small fraction of all trains. Upgrading all

This is true for many modern high-speed trains (though those tend to not be diesel trains...), but those are only a small fraction of all trains. Upgrading all existing freight cars with dedicated motors would be a crazy effort. Of course you could argue that freight trains aren't modern, which would make your comment correct in the worst sort of way ;-)