Conventionally, on a railroad, trains consist of a powered unit that pulls a number of unpowered railroad cars. More recently, on some trains, especially on suburban passenger routes, the trains are self-powered; all or many of the cars have their own engines or motors aboard (these are known as multiple units). Sometimes more than one locomotive is present, in a double-header, triple-header or, with modern locomotive, a consist of locomotives MU'ed together.

There are many reasons for this.

  • Efficiency: it's more efficient to have one large power units than multiple smaller ones.
  • Maintenance: a powered unit is more likely to fail than a non-powered one. Concentrating the power in a single locomotive means only the locomotive needs to be replaced if it fails.
  • Safety: Historically, power was a dangerous thing. Until the mid 20th century, most trains were powered by steam locomotives, which, if not operated carefully, can prove quite dangerous. Modern diesel locomotives and electric locomotives are not quite so demanding of care.

Railroad locomotives of the 20th century are large, powerful beasts. A number of the largest steam locomotives built in the US weighed over a million pounds; horsepower at the drawbar attained over 8,000.

Locomotives can be divided into several categories by type of power. These include

Lo"co*mo`tive (?), a. [Cf. F. locomotif. See Locomotion.]

1.

Moving from place to place; changing place, or able to change place; as, a locomotive animal.

2.

Used in producing motion; as, the locomotive organs of an animal.

 

© Webster 1913.


Lo"co*mo`tive (?), n.

A locomotive engine; a self-propelling wheel carriage, especially one which bears a steam boiler and one or more steam engines which communicate motion to the wheels and thus propel the carriage, -- used to convey goods or passengers, or to draw wagons, railroad cars, etc. See Illustration in Appendix.

Consolidation locomotive, a locomotive having four pairs of connected drivers. -- Locomotive car, a locomotive and a car combined in one vehicle; a dummy engine. [U.S.] -- Locomotive engine. Same as Locomotive, above. -- Mogul locomotive. See Mogul.

 

© Webster 1913.

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