It’s easy to grasp the main reasons trains are efficient: locomotives pulling many cars along a graded steel track. Steel, in comparison with rubber on asphalt, encounters far less friction. And that friction is not only a direct cost in gasoline, it is also hugely environmentally expensive in replacement and discarded tires. Tires consume energy to produce and operate. Feel them after a trip. That heat came from the repeated bending and contact with the road. Heat wears out the tires and the road, and the roads wear out the tires. Steel wheels and rails do not bend and they wear very little.
Large locomotive diesels are cleaner than the equivalent smaller truck diesel engines required to haul the same load. One big engine runs more efficiently than many smaller engines. As all trains consume less energy than highway vehicles right now, they will thus produce fewer greenhouse gases even when they directly or indirectly use fossil fuels.
Electric power plants are a cleaner fuel source than diesel locomotive engines. Electrified trains are most efficient and cleanest running of all. The Steel Interstate can run on electricity from any source as we develop wind, tidal, solar-thermal, photo voltaic and hydro sources, which produce virtually no greenhouse gases or other pollutants. The completed Steel Interstate System as we conceive it would run on completely sustainable energy sources. Rail corridors offer an extremely well connected existing right-of-way network for transmission of this power to cities and other points of use.