The Mount Washington Cog Railway, also known as the Cog, is the world's first mountain-climbing cog railway. The railway climbs Mount Washington in New Hampshire, United States. It uses a Marsh rack system and both steam and biodiesel-powered locomotives to carry tourists to the top of the mountain. Its track is built to a 4 ft 8 in gauge, which is technically a narrow gauge, as it is 1⁄2 inch (13 mm) less than a 4 ft 8+1⁄2 in standard gauge.