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Diesel electric train locomotives are serial hybrids. So the diesel engines are run a near constant RPM. And the electric traction motors have maximum torque at 0 RPM, and they are much more efficient.
Trucks have to use 17-22 speed transmissions and so they are at their maximum efficiency only a fraction of the time during acceleration.
And yes, trains have lower rolling resistance, and better overall aerodynamics, and economy of scale -- and we should start using them more to move freight.
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