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A tram (also known as tramcar; and in North America known as streetcar, trolley or trolley car) is a rail vehicle which runs on tracks along public urban streets (called street running), and also sometimes on a segregated right of way.〔(【引用サイトリンク】title=Tram - Definition and More from the Free Merriam-Webster Dictionary )〕 The lines or networks operated by tramcars are called tramways. Tramways powered by electricity, the most common type historically, were once called electric street railways. However, trams were widely used in urban areas before the universal adoption of electrification; other methods of powering trams are listed below under "History". Tram lines may also run between cities and/or towns (for example, interurbans, tram-train), and/or partially grade-separated even in the cities (light rail). Very occasionally, trams also carry freight. Tram vehicles are usually lighter and shorter than conventional :trains and rapid transit trains, but the size of trams (particularly light rail vehicles) is rapidly increasing. Some trams (for instance tram-trains) may also run on ordinary railway tracks, a tramway may be upgraded to a light rail or a rapid transit line, two urban tramways may be connected to an interurban, etc. For all these reasons, the differences between the various modes of rail transportation are often indistinct. Today, most trams use electrical power, usually fed by an overhead pantograph; in some cases by a sliding shoe on a third rail, trolley pole or bow collector. If necessary, they may have dual power systems — electricity in city streets, and diesel in more rural environments. Trams are now included in the wider term "light rail",〔Collins English Dictionary〕 which also includes segregated systems. In the United States, the term ''tram'' has sometimes been used for rubber-tired trackless trains, which are not related to the other vehicles covered in this article. ==Etymology and terminology== The English terms ''tram'' and ''tramway'' are derived from the Scots word ''tram'',〔() 〕 referring respectively to a type of truck used in coal mines, and the tracks on which they ran. The word ''tram'' probably derived from Middle Flemish ''trame'' ("beam, handle of a barrow, bar, rung"), a North Sea Germanic word of unknown origin meaning the beam or shaft of a barrow or sledge, also the barrow itself. The identical word ''la trame'' with the meaning "crossbeam" is also used in the French language. Etymologists believe that the word ''tram'' refers to the wooden beams the railway tracks were initially made of before the railroad pioneers switched to the much more resistant tracks made of steel.〔Duden-das Herkunftswörterbuch-Etymologie der deutschen Sprache-Mannheim 2001 p859〕 The word ''Tram-car'' is attested from 1873.〔(【引用サイトリンク】title=Online Etymology Dictionary )〕 Although the terms ''tram'' and ''tramway'' have been adopted by many languages, they are not used universally in English; North Americans prefer ''streetcar'', ''trolley'', or ''trolleycar''. The term ''streetcar'' is first recorded in 1840, and originally referred to horsecars. When electrification came, Americans began to speak of ''trolleycars'' or later, ''trolleys''. A widely held belief holds the word to derive from the ''troller'' (said to derive from the words ''traveler'' and ''roller''), a four-wheeled device that was dragged along dual overhead wires by a cable that connected the troller to the top of the car and collected electrical power from the overhead wires.; this portmanteau derivation is, however, most likely folk etymology. "Trolley" and variants refer to the verb ''troll'', meaning 'roll' and probably derived from Old French,〔(【引用サイトリンク】title=Online Etymology Dictionary )〕 and cognate uses of the word were well established for handcarts and horse drayage, as well as for nautical uses. The troller design frequently fell off the wires, and was soon replaced by other more reliable devices, the trolley pole and notably the bow collector. Both were fitted to the top of the car and were spring-loaded in order to keep, respectively, a small trolley wheel or grooved lubricated "skate" mounted at the top of the pole or a steel rod forming the top of the bow firmly in contact with the underside of the overhead wire. The terms ''trolley pole'' and ''trolley wheel'' both derive from the troller.〔Middleton, William D. (1967). ''The Time of the Trolley'', p. 60. Milwaukee: Kalmbach Publishing. ISBN 0-89024-013-2.〕 Trams using trolley-pole current collection are normally powered through a single pole, with return current earthed through the steel wheels and rails. Modern trams often have an overhead pantograph mechanical linkage to connect to power, abandoning the trolley pole altogether. The alternative North American term ''trolley'' may strictly speaking be considered incorrect, as the term can also be applied to cable cars, or conduit cars that instead draw power from an underground supply. Conventional diesel tourist buses decorated to look like streetcars are sometimes called ''trolleys'' in the US (tourist trolley). Furthering confusion, the term ''tram'' has instead been applied to open-sided, low-speed segmented vehicles on rubber tires generally used to ferry tourists short distances, for example on the Universal Studios backlot tour and, in many countries, as tourist transport to major destinations. Over time, the term ''trolley'' has fallen into informal use, and may be applied loosely to a wide variety of different vehicle types. The word has taken on a historic or picturesque connotation, and is often associated with tourist or leisure travel. In North America, professional or formal documents generally use more precise alternative terms, such as ''streetcar'' or ''light rail vehicle'' (LRV). Although the use of the term ''trolley'' for tram was not adopted in Europe, the term was later associated with the ''trolleybus'', a rubber-tyred vehicle running on hard pavement, which draws its power from pairs of overhead wires. These electric buses, which use twin trolley poles, are also called ''trackless trolleys'' (particularly in the northeastern US), or sometimes simply ''trolleys'' (in the UK, as well as in Seattle and Vancouver). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tram」の詳細全文を読む スポンサード リンク
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