A cog railway or rack and pinion railway is a mountain railway with a special centre rack rail[?] mounted in the middle of the sleepers[?] between the regular rails. The trains are fitted with one or more cog wheels that mesh into this rack rail (picture (http://www.pilatus.ch/images/zahnradbahn-stangen.jpg)). This then allows the locomotives to haul the train up steeply inclined slopes.
Examples:
Schneebergbahn
Mount Washington in New Hampshire, built in 1869, the only railway in the world built entirely on a trestle (3.1 miles or 5.2 km long).
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