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Trains and Railroads

Track

From the beginning of railroad development, British and European line surveyors were extremely careful to lay flat, even track, minimizing curves and grades. A track set down by George Stephenson, for instance, was laid on stone blocks with very compact foundations. By contrast, most early American tracks were laid hastily on wooden ties. The flimsy rails were easily deformed by the repeated weight of trains, sagging where not supported by the ties. Eventually the ends of the rails would rise up due to this sagging action. When they rose high enough, these "snake heads" would be pushed up in front of the wheels and either derail the train or punch through the floorboards, impaling those unlucky enough to be sitting above them. To avoid this, American railroads began placing the ties very close to one another, a practice still followed today.

The early wood rails were followed by brittle cast-iron rails. It was only later that more ductile wrought iron was used. Steel rail came into play in the 1870s, as a byproduct of the Bessemer process, a method for economical mass production of steel. The steel rail was more durable, capable of supporting harder wheels and heavier loads. In recent years, rails have become heavier, weighing as much as 100 lb (45 kg) per yard. Much of it is continuously welded rail. To simplify maintenance over miles of rail, special machines have been built that detect flaws in track, raise and align track, or clean and resettle track ballast.

Track gauge, or the width between the rails, varied tremendously in the early years of railroading. Gauges ranged from 3 ft (0.9 m) called "narrow gauge" lines to 6 ft (1.8 m) called "wide gauge" lines. Wide gauges were first believed to be more stable than narrow gauges, able to support broader cars without tipping over on curves. In mountainous areas or the highly populated urban regions of Britain, however, there was not sufficient room for wide gauge tracks, and rails were laid closer together. When it came time for the tracks of different railroads to merge into one enormous net, gauge discrepancies were a major problem.

The standard gauge was a 4 ft 8.5 in (1.7 m) spacing. Common in Britain, it was quickly passed along to other countries. In the United States, standard gauge became the official gauge of the American Railway Association toward the end of the nineteenth century. This led to changes in the rail spacing of narrow and wide gauge railroads, necessitating massively coordinated efforts in which the gauge of entire railway lines, as much as 500 or 600 mi (804-965 km), would be changed in a single day.


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Science EncyclopediaScience & Philosophy: Toxicology - Toxicology In Practice to TwinsTrains and Railroads - The Steam Locomotive, The First Locomotives, The American Standard, Diesel And Electric Locomotives, Track