Automatic platform gates

Platform screen doors (PSDs) and platform edge doors (PEDs) at train or subway stations screen the platform from the train. They are a relatively new addition to many metro systems around the world, some having been retrofitted to established systems. They are widely used in newer Asian and European metro systems.

The first stations in the world with platform screen doors are ten stations in the Saint Petersburg Metro's Line 2 that opened between 1961 and 1972. The platform "doors" are actually openings in the station wall, which support the ceiling of the platform. The track tunnels adjoining the ten stations' island platforms were built with tunnel boring machines (TBMs), and the island platforms were actually located in a separate vault between the two track tunnels. Usually, TBMs bore the deep-level tunnels between stations, while the station vaults are dug out manually and contain both the tracks and the platform. However, in the case of the Saint Petersburg Metro, the TBMs bored a pair of continuous tunnels that passed through ten stations, and the stations themselves were built in vaults that only contained the platform (with small openings on the sides of the vault, in order for passengers to access the trains in the tunnels). These openings were covered with steel doors in order to prevent people from falling into the gaps between the walls.

In 1987, the Singapore MRT was the first system in the world to install glass PSDs based on safety reasons, rather than based on architectural constraints.

Although the terms are often used interchangeably, platform screen doors can refer to both full-height and half-height barriers. Full height platform screen doors are total barriers between the station floor and ceiling, while the half-height platform screen doors are referred to as platform edge doors, as they do not reach the ceiling and thus do not create a total barrier. The half-screen doors are usually only half of the height of the full-screen doors, but they sometimes reach to the height of the train. These two types of platform screen doors are presently the main types in the world.

These doors help to:

Their primary disadvantage is their cost; installing a system typically costs several million USD per station. When used to retrofit older systems, they limit the kind of rolling stock that may be used on a line, as train doors must have exactly the same spacing as the platform doors; this results in additional costs due to depot upgrades and otherwise unnecessary purchases of rolling stock. They also impede natural ventilation, increasing climate control costs.

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Wikipedia