Narrow gauge refers to a railway system where the distance between the rails is less than the standard gauge of 1,435 mm (4 ft 8 1⁄2 in). Common narrow gauge measurements include 1,000 mm (3 ft 3 3⁄8 in) and 762 mm (2 ft 6 in). This type of railway is often used in mountainous or rugged terrain, where tighter curves and lighter construction are beneficial. Narrow gauge railways are typically more cost-effective to build and maintain, making them popular for industrial, mining, and tourist operations. Examples include the Darjeeling Himalayan Railway in India and the Cumbres and Toltec Scenic Railroad in the United States.