Why? It's Physics!

So… Exactly why is it that railroads are so much more efficient at hauling freight?

It boils down to physics. Specifically, two factors when moving matter across distances.

1. Less rolling friction. Steel wheels on steel rails create far less friction than does rubber on roads. Rolling friction is caused by the deformation of the wheel under a load which turns kinetic energy (useful) into heat (not useful). This is why truck tires are so big (fewer turns per mile generates less heat) and inflated at higher pressures (to reduce the amount of deformation). Steel train wheels deform insignificantly under tremendous loads.

2. Less aerodynamic drag. Aerodynamic drag arises from the need to push air out of the way at the front of the vehicle, then “put it back” to fill the hole in the atmosphere after it passes. A train, regardless of the number of railcars, has effectively one front where the air is compressed and one rear area where the air gets sucked back into place. If each railcar were 3 trucks on the road (typical railcar-to-truck hauling capacity ratio), there would be sources of aerodynamic drag at the front and at the rear of each truck. So, a 100-car train would have 2 prime sources of aerodynamic drag (one at the front and one at the rear) compared to 600 drag sources if 300 trucks were hauling the same amount of freight.