[Piwoslaw]

A smaller part of the savings is the greater cargo mass to overall mass ratio: A freight train is 1-4 locos and then 40-200 cars. With a very few exceptions, each truck trailer has it's own tractor, with it's own engine, A/C, etc. So if a truck weights 40tons, then the actual cargo is maybe 80% of that weight, while for a 10kton train the cargo is probably closer to 90%-95%. (I'm just guesstimating those numbers, so please correct me if I'm wrong.)

Also, once a truck gets off the highway it has to stop at every intersection, while a train can probably cross the continent withut stopping more than 3-4 times. Neither trucks nor trains have regenerative braking, though.