Narrow gauge railway

A narrow gauge railway (or narrow gauge railroad) is a railway that has a track gauge narrower than the 1,435 mm (4 ft 8½ in) of standard gauge railways. Most existing narrow gauge railways have gauges of 3 ft 6 in (1,067 mm) or less

Since narrow gauge railways are usually built with smaller radius curves and smaller structure gauges, they can be substantially cheaper to build, equip, and operate than standard gauge or broad gauge railways, particularly in mountainous 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 costs 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. On the other hand, standard gauge or broad gauge railways generally have a greater haulage capacity and allow greater speeds than narrow gauge systems.

Historically, many narrow gauge railways were built as part of specific industrial enterprises and were primarily industrial railways rather than general carriers. Some common uses for these industrial narrow gauge railways were mining, logging, construction, tunnelling, quarrying, and the conveying of agricultural products. Extensive narrow gauge networks were constructed in many parts of the world for these purposes. Significant sugarcane railways still operate in Cuba, Fiji, Java, the Philippines and in Queensland in Australia. Narrow gauge railway equipment remains in common use for the construction of tunnels.

The other significant reason for narrow gauge railways to be constructed was to take advantage of reduced construction costs in mountainous or difficult terrain, hence the national railway systems of countries such as Indonesia, Japan and New Zealand are primarily or solely narrow gauge. Trench railways of the World War I western front demonstrate a brief military application of this advantage. Non-industrial 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, India, and Costa Rica. Another country with a notable national railway built to narrow gauge is South Africa where the "Cape gauge" of 3 ft 6 in (1,067 mm) is the most common gauge. In India, the narrow gauge system is slowly being converted to broad gauge, although some of India's most famous railways, the Darjeeling Himalayan Railway and Kalka-Shimla Railway are both narrow gauge. All 1,000 mm (3 ft 3⅜ in) (metre gauge) railways are being converted to 5 ft 6 in (1,676 mm) (broad gauge) under the Unigauge project.