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 locomotive
The reciprocating mechanism on the driving wheels of a two-cylinder single expansion steam locomotive tended to pound the rails (see hammer blow), thus requiring more maintenance. Raising steam from coal took a matter of hours, and created serious pollution problems. Coal-burning locomotives required fire cleaning and ash removal between turns of duty. Diesel or electric locomotives, by comparison, drew benefit from new custom-built servicing facilities. The smoke from steam locomotives was also deemed objectionable; the first electric and diesel locomotives were developed in response to smoke abatement requirements, although this did not take into account the high level of less-visible pollution in diesel exhaust smoke, especially when idling. In some countries, however, power for electric locomotives is derived from steam generated in power stations, which are often run by coal.