The majority of monorails are powered by electric motors that receive current from a third rail, contact wire or electrified channel attached to the guidance beam on which they rest. Other locomotive technologies in use in monorails include hybrid diesel engines and electromagnetic propulsion systems.
Introduced at the start of the 20th century, monorails are distinguished from other light rail systems by a single beam, which is typically narrower than the body of the train, that guides and supports the vehicle. To prevent the carriages from swaying side-to-side as the train moves along its single beam, a series of small rubberized tires clamp around the beam to hold it steady. The carriages of a monorail may either sit on top of or be suspended beneath the beam. Straddle-beam designs are the most commonly used as of 2014. In both designs, horizontal wheels on the cars make contact with the power supply and transfer electricity to the engines via conductive shoes. The engines are operated by the conductor from one of the master control units located in cabs on both ends of the train. This dual-control system allows the train to travel equally well in either direction without having to turn around.