Railway platform height is the built height – above top of rail (ATR) – of passenger platforms at stations. A connected term is train floor height, which refers to the ATR height of the floor of rail vehicles. Worldwide, there are many, frequently incompatible, standards for platform heights and train floor heights. Where raised platforms are in use, train widths must also be compatible, in order to avoid both large gaps between platforms and trains and mechanical interference liable to cause equipment damage.