Narrow-gauge
A narrow-gauge railway (or narrow-gauge railroad in the US) is a railway with a track gauge narrower than the 1,435 mm (4 ft 8 1⁄2 in) of standard gauge railways. Most existing narrow-gauge railways are between 600 mm (1 ft 11 5⁄8 in) and 1,067 mm (3 ft 6 in).
Since narrow-gauge railways are usually built with smaller radius curves, smaller structure gauges, lighter rails, etc., they can be substantially less costly to build, equip, and operate than standard gauge or broad gauge railways, particularly in mountainous or difficult terrain. The lower costs of narrow-gauge railways mean they are often built to serve industries and communities where the traffic potential would not justify the cost of building a standard or broad gauge line.
Narrow-gauge railways also have specialized use in mines and other environments where a very small structure gauge makes a very small loading gauge necessary. Narrow-gauge railways also have more general applications. Nonindustrial narrow-gauge mountain railways are or were common in the Rocky Mountains of the United States and the Pacific Cordillera of Canada, in Mexico, Switzerland, the former Yugoslavia, Greece, and Costa Rica. In some countries, narrow gauge is the standard, like the 3 ft 6 in (1,067 mm) gauge in Japan, Indonesia, Taiwan, New Zealand, South Africa, the Australian states of Queensland and Tasmania, and the 1,000 mm (3 ft 3 3⁄8 in) metre gauge in Malaysia and Thailand.
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