Lowered overall wind resistance also plays a significant part. With Semi's, each separate truck has to endure its own wind resistance independently. With a tr

Lowered overall wind resistance also plays a significant part. With Semi's, each separate truck has to endure its own wind resistance independently. With a train, each rail car effectively drafts the car in front, producing significant reductions in wind resistance for all cars behind the locomotive. This site (https://www.energy.gov/eere/vehicles/parasitic-loss-reduction-research-and-development https://www.energy.gov/eere/vehicles/parasitic-loss-reductio...) quotes wind resistance, braking, and rolling resistance as responsible for a 45% reduction in efficiency. This site (https://www.nap.edu/read/13288/chapter/7 https://www.nap.edu/read/13288/chapter/7) has a table that separates the factors out. Of the parasitic losses, aerodynamic losses (i.e., wind resistance) is responsible for consuming 53% of the motive power.