The escalator is a set of moving stairs that transports people from one floor to another in a department store, airport, or other public place. Underneath the stairs is a continuous belt that moves around wheels. The stairs are attached to two side belts or to one central belt, which is driven by electricity. The moving handrails on both sides of the escalator work the same way and are timed at the same speed as the steps. At the top and bottom of the escalator, the steps fold flat so they can move underneath the floor, and after traveling around the belt they open up and start again. The same set of steps can be used to run up or down, depending on the direction in which the belt is driven.