If only the car companies would use the same technology as those CSX trains they advertise as getting 500 miles per gallon. :-)
Trains run on tracks, with steel wheels, and, typically, very small slopes to climb. However, if you divide weight by horsepower, and use a diesel engine in your car (with that power to weigh ratio) use a cv transmission, and can put up with almost no acceleration, you can probably get the same mileage per ton.
DG