A rack railway is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with this rack rail. This allows the trains to operate on steep grades above 10%, which is the maximum for friction-based rail. Most rack railways are mountain railways, although a few are transit railways or tramways built to overcome a steep gradient in an urban environment.
Locomotive 7 of the Vitznau-Rigi-Bahn, one of the last operational locomotives with a vertical boiler
The Pikes Peak Cog Railway is the highest rack railway in the world, at 14,115 ft (4,302 m).
The Pilatus Railway is the steepest rack railway in the world, with a maximum gradient of 48% and an average gradient of 35%.
The Mount Washington Cog Railway is the oldest mountain-climbing rack railway in the world, opening in 1868.
A rack and pinion is a type of linear actuator that comprises a circular gear engaging a linear gear. Together, they convert between rotational motion and linear motion. Rotating the pinion causes the rack to be driven in a line. Conversely, moving the rack linearly will cause the pinion to rotate. A rack-and-pinion drive can use both straight and helical gears. Though some suggest helical gears are quieter in operation, no hard evidence supports this theory. Helical racks, while being more affordable, have proven to increase side torque on the datums, increasing operating temperature leading to premature wear. Straight racks require a lower driving force and offer increased torque and speed per fraction of gear ratio which allows lower operating temperature and lessens viscal friction and energy use. The maximum force that can be transmitted in a rack-and-pinion mechanism is determined by the torque on the pinion and its size, or, conversely, by the force on the rack and the size of the pinion.
Lock gate controls on a canal
Rack steering in an automobile
Rack railway axle (wheelset)
Funicular wheelset with Abt rack-and-pinion brake