Buffer stop

Two views of a Hayes-built bumper at the Linden Railroad Museum, Linden, Indiana. This design accommodates the AAR coupler.

Energy-absorbing buffer stop in France

This buffer stop is designed to move up to 7 metres (23 ft) to slow down a 850 tonnes (840 long tons; 940 short tons) passenger train from 15 km/h (9.3 mph) without damaging the train or injuring passengers.

A buffer stop or bumper (US) is a device to prevent railway vehicles from going past the end of a physical 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.

Types

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.

Energy-absorbing

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 (i.e. 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.

Wheel stop

Wheel stops are used to stop slow moving trains from continuing down a level track section.

Examples

• Raja Trains Depot in Tehran
  • Stopping speed: 20 km/h (12 mph)
  • Stopping distance: 20 m (66 ft)

Accidents

The aftermath of the Gare Montparnasse accident

• 22 October 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
• 1908 – at the Top Points of the Lithgow Zig Zag, a train failed to stop at the buffer stops, stopping precariously at a precipice over the valley below.
• 1948 – diesel train through buffer stops at Los Angeles.
• 15 January 1953 – Union Station, Washington, D.C. – Federal Express #173, pulled by PRR 4876, overruns the buffer stop after its brakes fail. The locomotive stops in the concourse before falling through the floor. A temporary floor was built over it for the upcoming inauguration of Dwight D. Eisenhower before it was shipped back to Altoona, Pennsylvania in three pieces for repairs.
• 1970s – BART train went through buffer stops due to fault in automatic train operation.
• 28 February 1975 – Moorgate Underground rail crash – 43 killed, 74 injured – buffer stop collision made far worse by large dimensioned dead end tunnel beyond.
• 13 April 1978 – Budapest, Hungary – commuter train overruns a buffer stop owing to brake failure and crashes into the station building. 13 killed, 25 injured.
• 8 November 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 – Template:Class 318electric 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.
• 21 December 2009 – Zagreb, Croatia – commuter train number 5100 from Sisak Caprag crashed into the platform bumper. The cause was antifreeze fluid in the locomotive's braking system which had frozen due to the extremely low outside temperature (-22°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 that his brakes had failed and that the train would crash at the end of the platform.
• 25 July 2010 – Stavoren railway station, the Netherlands – A maintenance train collided with a buffer stop at the single-track terminus station. The train rammed a small shop, passed through it and stopped at the square behind it. Only two people were injured, out of four people on the train. The accident happened late at night, when passenger services had already finished. The cause is being investigated.
• 2 March 2011 - San Francisco 4th and King Street Station, San Francisco, California - A Caltrain commuter train failed to stop before hitting the buffer stop. Multiple minor injuries reported.
• 8 May 2011 - Hoboken Terminal, New Jersey - A Port Authority Trans-Hudson rapid transit train crashes into a bumper. At least 34 are injured, none critically. The cause is being investigated.

See also

• List of rail accidents