Doors placed along a platform edge to separate passengers from the exposed railway. Usually only used on metro systems (e.g. Singapore, Lille France, Lenningrad Russia, Kobe Japan) where they are designed to match the train doorways. Their use may be justified for safety reasons or where there are extremes of climate when they can assist with reducing energy wastage. They are however, expensive at over US$1.5 million a platform edge and they add another reliability and maintenance dimension. Also known as Platform Edge Doors (PEDs)