Fuel consumption is directly related to the amount of work done. The locomotive moving alone travels 10 miles at a constant 50 mph, on level track. Let's use these relationships. The truck weighs 20,000 lbs. This difference is why diesel engines are good for weight hauling, since they can apply high torque at low speeds, as used in locomotives.
Gasoline engines are good for rapid acceleration, as used in automobiles.
Steam locomotive did not have nearly the same starting torque as a diesel. Diesel can pull more than a steam locomotive with the same horsepower. This and lower maintenance and operating costs led to the replacement of steam locomotives by diesel-electrics. Want to get torque and power of engine transmitted to the wheels. Purpose of transmissions transfer power from engine to drive wheels while producing a reduction in engine speed and providing flexible control.