escalator
Each step on the endless belt forming an escalator has two pairs of wheels. The upper pair (1) run on an outer rail and the lower ones (2) run on an inner rail. On the sloping part of the "staircase", the rails are in line. But at the top and the bottom they are separate to make the steps line up to create flat sections for people to step on and off. Even when stopped, an escalator can be used.
An escalator is a set of electrically-powered moving stairs, driven by chain and sprocket and held in the correct plane by two tracks. It is usually inclined at 30° and limited to a total rise of up to 18 meters (60 feet). As the steps approach the landing, they pass through a protective comb-like device. Escalators are used to carry pedestrians between floors in busy areas such as large stored, office buildings, and underground railway stations. The Otis Elevator Company exhibited the first escalator in 1900 at the Paris Exposition.
