LOCOMOTIVE

any of various self-propelled vehicles used for hauling railroad cars on tracks. Although motive power can be incorporated into a car that also has passenger, baggage, or freight accomodations, it most often is provided by a separate unit, the locomotive, which includes the machinery to generate (or, in the case of an electric locomotive, to convert) power and transmit it to the driving wheels. Today there are two main sources of power for a locomotive: oil (in the form of diesel fuel) and electricity. Steam, the earliest form of propulsion, was in almost universal use until about the time of World War II; since then it has been superseded by the more efficient diesel and electric traction. The steam locomotive is a self-sufficient unit, carrying its own water supply for generating the steam and coal, oil, or wood for heating the boiler. The diesel locomotive also carries its own fuel supply, but the diesel-engine output cannot be coupled directly to the wheels; instead, a mechanical, electric, or hydraulic transmission must be used. The electric locomotive is not self-sufficient; it picks up current from an overhead wire or a third rail beside the running rails. Third-rail supply is employed only by urban rapid-transit railroads operating on low-voltage direct current. In the 1950s and '60s the gas turbine was adopted by one American and some European railroads as an alternative to the diesel engine, but its advantages were subsequently nullified by advances in diesel traction technology and increases in oil price. In 1990 this form of traction survived only in some self-powered passenger train-sets of the French and Egyptian railways and of the U.S. passenger train operator, Amtrak (National Railroad Passenger Corporation). Thomas Clark Shedd Geoffrey Freeman Allen any of various self-propelled vehicles used for hauling railroad cars on tracks. The New Castle, built by Richard Trevithick in 1803, the first locomotive to do actual work. The three main sources of power for locomotives are steam, electricity, and oil. The first locomotive to do actual work, the New Castle built in 1803 by Richard Trevithick for a Welsh tramroad, was too heavy for the iron rails of the time (see photograph). The first practical locomotive was built in 1812 by John Blenkinsop, an inspector at the Middleton colliery near Leeds, Eng. Two vertical cylinders drove two shafts that in turn were geared to a toothed wheel that meshed with a rack rail. By 1829 the English engineer George Stephenson had developed a locomotive, the Rocket, that was the prototype for the modern steam locomotive. Instead of the single-flue boiler that had been used until then, Stephenson created a multiple fire-tube boiler. The Rocket also exhausted steam and created a draft in its firebox in the manner of modern locomotives. Its pistons were connected to a single pair of driving wheels that were flanged on the inside to keep them from sliding off the rails. In the United States John Stevens ran the first locomotive in 1825 on a three-rail track, the centre rail engaging a toothed wheel on the engine. From the single pair of driving wheels on the Rocket, locomotives were soon developed with four coupled wheels, relying for traction on the simple friction produced between the wheels and the rails by the weight of the engine. Until well after 1865, an engine with four driving wheels and four pilot (or leading) wheels to guide it around curves was the dominant locomotive type in the United States; it was known as the American Standard. Like all steam locomotives, it heated water to boiling, then channelled the resulting steam into a cylinder. The great force of escaping steam drove a piston that was linked to the driving wheels, causing them to revolve and to move the locomotive and the rest of the train. In the 20th century steam locomotives became huge, sophisticated machines capable of moving freight trains of 200 cars at 75 miles (120 kilometres) per hour. The drive wheels became as much as seven feet (two metres) in diameter, and on the largest engines their number was increased to 16. Smaller trailing wheels behind the drivers supported even larger fireboxes that heated water in immense horizontal boilers. Smaller locomotives, especially in Europe, carried their own fuel (coal or sometimes oil), but most carried their fuel and water in a car coupled behind them. Steam locomotives were simple and could withstand much wear and tear; but they required extensive servicing after relatively short trips, tended to kink rails because of their pounding motion, and needed separate crews for each engine. Their thermal efficiency was seldom greater than about 6 percent because of incomplete combustion and heat losses. For these reasons, the steam locomotive is practically extinct. Only in China and in some parts of India and sub-Saharan Africa are steam locomotives still in daily use. Even as steam locomotives were being developed, designers were experimenting with the idea of using electricity for motive power. Batteries were tried as early as 1835, but it was not until 1879 that the first practical electric locomotive was run at an exhibition in Berlin. In the United States the Baltimore and Ohio Railroad ran an electric locomotive under Baltimore harbour in 1895; in Italy electric locomotives were operating on main lines by 1902. Unlike steam and diesel-electric locomotives, which produce their own power, electric locomotives simply convert the electric power that is generated elsewhere. They can thus develop more power than their rated capacity for short times when subject to increased loads, such as climbing a steep grade or starting a heavy train. Because of their simpler machinery, they require less maintenance, their maintenance costs are much lower, and they last longer than diesel-electrics. In order to be economical, however, electric traction requires the availability of cheap electricity. The traffic density must also be heavy enough to justify the high cost of maintaining generating facilities and the overhead wires or trackside rail that carry electric current to the locomotive. In the Scandinavian countries and Italy more than one-half of the railroad route miles are electrified, and in France about one-third. In the United States, however, only about 1 percent of the railroad routes are electrified; these are mostly in the Northeast between major cities. The diesel-electric locomotive uses a diesel engine to run a generator that produces electricity for traction motors geared directly to the axles of the engine. Diesel switching engines were in use by 1925. Main-line diesel service was launched in Germany in 1932, with a two-car, streamlined train that was capable of running at an average speed of 77 miles per hour. In 1935 passenger engines were in use in the United States, and by 1939 the first freight units were being built. Although the use of steam locomotives was prolonged by World War II, after the war diesels quickly supplanted steam, first in North America and then in Europe. The thermal efficiency of diesels is about four times as great as that of steam locomotives, and they thus require substantially less fuel for equivalent power. They can accelerate more quickly, run at higher speeds with less damage to the track, and require less servicing than steam engines. Diesels also function with the efficiency of electric locomotives (within the limits of their power-generating capacity) but do not require the capital investment in substations and electrical-distribution networks needed by electrics. Especially attractive to railroad management is the diesel's flexibility: Many units can be combined according to the power needed for a particular train with only one crew required for all the units. There has also been a substantial amount of experimentation with turbines as alternate sources of motive power. One successful model is a passenger train powered by aircraft-type turbines that went into service in the United States and Canada in 1969. Other trains have been developed that use gas turbines and turbine-electric combinations. Additional reading Current developments in railway transportation are documented and interpreted in Jane's World Railways (annual). The history of railway technology is presented in Geoffrey Freeman Allen, Railways: Past, Present & Future (1982); George H. Drury (comp.), The Historical Guide to North American Railroads, updated ed. (1991); Lucius Beebe and Charles Clegg, Hear the Train Blow: A Pictorial Epic of America in the Railroad Age (1952); Geoffrey Freeman Allen, Railways of the Twentieth Century (1983); and Gustav Reder, The World of Steam Locomotives (1974; originally published in German, 1974). Other aspects of railway technology are studied in O.S. Nock (ed.), Railway Signalling (1980); and Coenraad Esveld, Modern Railway Track (1989). Geoffrey Freeman Allen, The Fastest Trains in the World (1978); and Joseph Vranich, Supertrains: Solutions to America's Transportation Gridlock (1991), discuss high-speed passenger trains. For the history of the railway passenger car, see Arthur D. Dubin, Some Classic Trains (1964, reprinted 1975), and More Classic Trains (1974, reprinted 1990); Lucius Beebe and Charles Clegg, The Trains We Rode, 2 vol. (196566, reissued in 1 vol., 1990); and Geoffrey Freeman Allen, Luxury Trains of the World (1979); and, for the history of a related institution, see Carroll L.V. Meeks, The Railroad Station: An Architectural History (1956, reissued 1978). Geoffrey Freeman Allen