Escalators are moving staircases that operate in conveyor-belt fashion and carry passengers between two floors. A continuous length of inter-connected but movable stairs is held together by a flexible chain that loops around two toothed gears, the upper one driven by a motor. Each stair has a pair of rollers on either side that sit in grooved rails. The position of the stairs depends on the rails. The stairs pivot up as they ride toward the drive gear and sink down, locking into place to form a smooth surface, as each one reaches the top.