Dieselisation
Dieselisation took place largely because of the tremendous reduction in operating costs it allowed. Steam locomotives require large pools of labour to clean, load, maintain and run. They also require extensive service, coaling and watering facilities. This was their biggest inferior measure as compared to the diesel locomotive in the number of ton-miles or passenger traffic miles either could run. Diesels could and did have a significantly higher initial price per unit-horsepower delivered. However, their far greater range between fueling stops, the absence of water stops, and the much higher unit availability between inspection repair and maintenance stops, were far better than steam. Diesels simply required significantly less time and labour to operate and maintain. Diesel power was also more scalable to power requirements, owing to the control systems that allowed multiple units to be controlled by one operator. "Double header" steam power required a crew for each locomotive. Initially, diesel locomotives were less powerful than the typical steam locomotives. Between the late 1930s and the late 1950s the power available with diesel locomotive engines roughly doubled, although the most powerful steam locomotives ever built still exceeded the power of the most powerful diesel locomotives from the late Twentieth Century.
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.