Diesel locomotive
Diesel locomotives offer significant operating advantages over steam locomotives. They can safely be operated by one person, making them ideal for switching/shunting duties in yards (although for safety reasons many main-line diesel locomotives continue to have 2-man crews: an engineer and a conductor/switchman) and the operating environment is much more attractive, being quieter, fully weatherproof and without the dirt and heat that is an inevitable part of operating a steam locomotive. Diesel locomotives can be worked in multiple with a single crew controlling multiple locomotives in a single train — something not practical with steam locomotives. This brought greater efficiencies to the operator, as individual locomotives could be relatively low-powered for use as a single unit on light duties but marshaled together to provide the power needed on a heavy train. With steam traction a single very powerful and expensive locomotive was required for the heaviest trains or the operator resorted to double heading with multiple locomotives and crews, a method which was also expensive and brought with it its own operating difficulties.
Steam motor
The principle of the steam motor is to use the developments of the high-speed steam engine, and to apply them to light locomotives. Rather than a large conventional locomotive having only two cylinders, rotating at the speed of the driving wheels, the steam motor uses several small cylinders geared to run at high speeds. With all other factors remaining the same, doubling the speed of a piston engine doubles its power. The steam motor allowed small, light engines to be used. As many of the engine's performance losses remain constant, or are also related to the engine size, these small engines could also be more efficient overall.