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1957741

Platform screen doors

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1957741

Platform screen doors

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Platform screen doors

Platform screen doors (PSDs), also known as platform edge doors (PEDs), are used at some train, rapid transit and people mover stations to separate the platform from train tracks, as well as on some bus rapid transit, tram and light rail systems. Primarily used for passenger safety, 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, and Latin American bus rapid transit systems.

The idea of platform edge doors dates from as early as 1908, when Charles S. Shute of Boston was granted a patent for "Safety fence and gate for railway-platforms". The invention consisted of "a fence for railway platform edges", composed of a series of pickets bolted to the platform edge, and vertically movable pickets that could retract into a platform edge when there was a train in the station. In 1917, Carl Albert West was granted a patent for "Gate for subrailways and the like". The invention provided for spaced guides secured to a tunnel's side wall, with "a gate having its ends guided in the guides, the ends and intermediate portions of the gate having rollers engaging the side wall". Pneumatic cylinders with pistons would be used to raise the gates above the platform when a train was in the station. Unlike Shute's invention, the entire platform gate was movable, and was to retract upward.

The first stations in the world with platform screen doors were the ten stations of the Saint Petersburg Metro's Line 2 that opened between 1961 and 1972. The platform "doors" are actually openings in the station wall which supports 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 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.

Singapore's Mass Rapid Transit, opened in 1987, is often described as the first heavy Metro system in the world to incorporate PSDs into its stations for climate control and safety reasons, rather than architectural constraints, though the light Lille Metro, opened in 1983, predates it.

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 or automatic platform gates, as they do not reach the ceiling and thus do not create a total barrier. Platform gates are usually only half of the height of the full-screen doors, are chest-height sliding doors at the edge of railway platforms to prevent passengers from falling off the platform edge onto the railway tracks. But they sometimes reach to the height of the train. Like full-height platform screen doors, these platform gates slide open or close simultaneously with the train doors. These two types of platform screen doors are presently the main types in the world.

The doors help to:

Their primary disadvantage of PSDs is their cost. When used to retrofit older systems, they can limit the kind of rolling stock that may be used on a line, because the train doors must fit the spacing of the platform doors, which can result in additional costs, due to the otherwise unnecessary purchase of new rolling stock and consequent depot upgrades.

Despite delivering an overwhelming improvement to passenger safety at the platform-train interface, platform screen doors do introduce new hazards which must be carefully managed in design and delivery. The principal hazard is entrapment between closed platform doors and the train carriage which, if undetected, can lead to fatality when the train begins to move (see § Incidents). Cases of this happening are rare, and the risk can be minimised with careful design, in particular by interlocking the door system with the signalling system, and by minimising the gap between the closed platform doors and the train body. In some cases active monitoring systems are used to monitor this gap.

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