A narrow-gauge railway (or narrow-gauge railroad) 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 3 ft 6 in (1,067 mm).
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.
