It's torque. If you see a freight train starting up it is excruciatingly slow to get going. Also, rolling stock has a lot less friction than trailers/cars w

It's torque. If you see a freight train starting up it is excruciatingly slow to get going. Also, rolling stock has a lot less friction than trailers/cars with tires; so once up to speed, a lot less hp per pound is required to maintain that speed compared to something like a semi trailer.