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A buffer stop or bumper (US) is a device to prevent railway vehicles from going past the end of a section of track.
The design of the buffer stop is dependent in part upon the kind of couplings that the railway uses, since the coupling gear is the first part of the vehicle that the buffer stop touches. The term buffer stop is itself of British origin, railways in Great Britain principally using buffer-and-screw couplings between vehicles.
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Energy-absorbing buffer stops
Due to its mass, a train transfers an enormous amount of kinetic energy in a collision with a buffer stop. Rigid buffers can only safely cope with very low-speed impacts (ie – nearly stationary). To improve stopping performance, a way of dissipating this energy is needed, through compression or friction. Following a buffer stop accident at Frankfurt-am-Main in 1902, the Rawie company developed a large range of energy-absorbing buffer stops. Similar hydraulic buffer stops were developed by Ransomes & Rapier in the UK.
Types of buffer stops
Several different designs have been developed for buffer stops, depending on the coupling system in use.
- Buffer stops with anticlimbers
- Buffer stops for a knuckle coupler (centrally positioned between the two rails)
- Buffer stops with traditional "buffers" on either side
- Hydraulic buffer stops
- Friction buffer stops (bolted down to the rail)
In rapid transit applications, hitting the bumper block is usually a very bad thing, because of the number of passengers involved and the confined space of the tunnel. Rapid transit systems have developed buffer stops that have built-in corrugated anticlimbers that engage and interlock with the anticlimbers on the car's end sill, which prevents telescoping of the cars during impact. These bumper blocks can be identified by their distinctive 'fins' appearance.
If there is extra room behind the bumper block, there is usually a sand or ballast drag that is designed to further retard a runaway train. One such accident occurred when a Northern Line train powered past the bumper block at Moorgate station in 1975 on the London Underground system.
Damage
To reduce the chance of damaging the expensive auto couplings, the bufferstop should have a depression matching the position of this coupling.
Simple bufferstops
If a full friction buffer stop is not needed, a timber sleeper fixed across the two rails can be used.
At Chatswood the catchpoint from the turnback siding ends in a pile of ballast.
Example
Alternatives
Lower cost alternatives to a buffer stop include railroad ties fixed to the rails, or a pile of dirt.
Warning lights
Buffer stops sometimes have a fixed red light associated with them.
Accidents
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- October 22, 1895 – Gare Montparnasse, Paris, France: express train overruns buffer stop and falls into street below.
- 1902 – Frankfurt am Main, Germany: Serious buffer stop collision inspires development of Rawie range of energy-absorbing buffer stops.
- 27 July 1903; Glasgow St Enoch, 16 killed 27 injured
- 1948 - diesel train through buffer stops at Los Angeles.[citation needed]
- 1970s - BART train went through buffer stops due to fault in automatic train operation.[citation needed]
- 28 February 1975 - Moorgate Underground rail crash, 43 killed, 74 injured - buffer stop collision made far worse by narrow dimensioned dead end tunnel beyond.
April 13, 1978 – Budapest, Hungary: commuter train overruns a buffer stop owing to brake failure and crashes into the station building. 13 killed, 25 injured.
- November 8, 1986 – Hua Lamphong, Bangkok, Thailand: 5 killed, 7 injured - buffer stop collision made by an unmanned train at a speed of 50 km/h.
- 8 January 1991 - Cannon Street station rail crash, London; 2 killed, 200+ injured - commuter train hits buffer stops.
- 11 July 1995 - Largs - electric train goes through buffer stops.
- 26 October 2006 - Kuala Lumpur buffer stop accident - a Star LRT train goes through buffer stops at the end of a stabling area (turnback perhaps) and ends up dangling over street. The train appears to have been empty of passengers.[3]
- December 21, 2009 – Zagreb, Croatia - commuter train number 5100 from Sisak Caprag crashed into the platform bumper. The cause was of antifreeze fluid in the locomotive's braking system which has frozen due to the extremely low outside temperature (-22 deg. C). Luckily, the speed of the train was only between 15 and 20 km/h. 60 people from the train (including train's engineer) were injured, 7 of them seriously. There were no injuries among people on the platform. The engineer leaned out of the cab window to warn people on the platform his brakes have failed and the train will crash at the end of the platform.[4].
See also
References
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