Each step is mounted on a four-wheeled carriage, attached to an endless chain. The front wheels run on one pair of rails, and the rear wheels on another pair. The two sets of rails are so arranged that the carriage and its step are always level. At the bottom and top a number of steps form a platform. As they approach the incline they gradually separate vertically into a staircase, but become a platform again as they reach the top or bottom, as the case may be. The chain is driven at a steady speed by a powerful electric motor.