In North America and Europe, and in much of the rest of the world, it has since been replaced by the diesel-electric locomotive. Modern steam engines are maintained only in countries where coal is much cheaper or more readily available than oil such as in China. In areas of high rail traffic, as along the United States East coast and in Central Europe, many rail lines have been electrified and use electric locomotives. Many a large locomotive actually develops enough power to supply a small city. Most of the time, however, only a small fraction of this power is needed to pull the train, and only a few pounds of tractive effort, or pulling power, is required to keep 1 ton of the train's weight in motion once it is under way.
Full power is needed principally to start the train or to pull it up a steep grade.
To start a long train, the locomotive first backs up to loosen the couplings between cars so that in the forward motion one car after the other begins moving. The old reciprocating steam locomotive is driven by a steam engine. Connecting rods from the pistons then move the driving wheels. The firebox at the rear end of the boiler is fed with coal or oil, which in a large locomotive is stored in a separate tender. The tender also contains the water that is turned into steam.