Wrong-side failure
Encyclopedia
A wrong side failure describes a failure condition in a piece of railway signalling
equipment that results in an unsafe state.
A typical example would be a signal showing a 'proceed' aspect (e.g. green) when it should be showing a 'stop' or 'danger' aspect, resulting in a "false clear". (The converse is a right side failure, where even with any reduction the resulting state is safe overall.)
that has to energize to show a green
light.
If a wire breaks, or the battery is drained, then the relay will de-energize and the signal will show a red
light, which is fail-safe
.
If a stray wire from another circuit touches the wire connected to that same relay, then that would be a wrong side failure, which is potentially dangerous. This stray wire can be guarded against by ensuring that the insulation on the relay wire is of good quality, and that all terminals are locked away.
In addition, the relay may be double-switched
, that is to say that it only energizes if a positive circuit and a negative circuit are both complete. That would then require two stray wires to cause a wrong side failure, which is much less likely than a single stray wire.
, but investigations soon showed that a wrong-side failure was not the cause.
The 2008 Chatsworth train collision
was determined to be human error, not wrong side failure as a few initially said.
.
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...
equipment that results in an unsafe state.
A typical example would be a signal showing a 'proceed' aspect (e.g. green) when it should be showing a 'stop' or 'danger' aspect, resulting in a "false clear". (The converse is a right side failure, where even with any reduction the resulting state is safe overall.)
Example of how a wrong side failure may occur
Consider a relayRelay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
that has to energize to show a green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
light.
If a wire breaks, or the battery is drained, then the relay will de-energize and the signal will show a red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
light, which is fail-safe
Fail-safe
A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....
.
If a stray wire from another circuit touches the wire connected to that same relay, then that would be a wrong side failure, which is potentially dangerous. This stray wire can be guarded against by ensuring that the insulation on the relay wire is of good quality, and that all terminals are locked away.
In addition, the relay may be double-switched
Double switching
frame|right|A single-switched relay can close inadvertently in response to a single false feed current.frame|right|A double-switched relay cannot close inadvertently with the application of the same current...
, that is to say that it only energizes if a positive circuit and a negative circuit are both complete. That would then require two stray wires to cause a wrong side failure, which is much less likely than a single stray wire.
Accidents
While accidents from the problem are rare, they do occur:- 1876 - Abbots Ripton rail disaster - signals frozen by blizzardBlizzardA blizzard is a severe snowstorm characterized by strong winds. By definition, the difference between blizzard and a snowstorm is the strength of the wind. To be a blizzard, a snow storm must have winds in excess of with blowing or drifting snow which reduces visibility to 400 meters or ¼ mile or...
in 'clear' position (signal arm hidden in a slot in the post).
- 1938 - Charing Cross (Northern Line) tube crashCharing Cross (Northern Line) tube crashThe Charing Cross tube crash occurred at 08:32 hours on 10 March 1938, when two Northern Line trains collided near Charing Cross . Twelve people were slightly injured. The cause was a wrong-side failure of the automatic signals; an electrician had rewired a faulty signal, S94B, so that it showed...
- signal linesman rewires a faulty signal incorrectly, so that it shows green too soon; two UndergroundLondon UndergroundThe London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...
trains collide as a result, injuring twelve. Also Charing Cross (District Line) tube crashCharing Cross (District Line) tube crashThe Charing Cross tube crash occurred on 17 May 1938 at about 09:55 hours, between Charing Cross and Temple stations...
, signal linesman makes wiring error in cabin, two UndergroundLondon UndergroundThe London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...
trains collide, killing six.
- 1953 - Sydenham Rail DisasterSydenham Rail DisasterThe Sydenham rail disaster occurred on 19 December 1953 when a New South Wales Government Railways electric passenger train travelling to Bankstown ran into the rear of another electric train travelling to East Hills at Sydenham....
- five killed
- 1976 - Glenbrook, New South Wales. Automatic signal in rear of a stationary EMU at "caution" when it should have been at "danger". Following goods train enters occupied signal section and collides with EMU; 1 passenger killed. Cause attributable to deteriorated wiring which allowed a false feed.
- 1979 - Invergowrie rail crashInvergowrie rail crashThe Invergowrie rail accident happened at Invergowrie in Scotland on 22 October 1979. The accident killed 5 people and injured 51 others.-Accident:...
- signal was at "wrong" (i.e. indistinct indication) yet taken by driver to be a 'proceed' signal.
- 1988 - Clapham Junction rail crashClapham Junction rail crashThe Clapham Junction rail crash was a serious railway accident involving two collisions between three commuter trains at 08:10 on the morning of Monday, 12 December 1988....
- single stray wire causes false green signal and collision killing 35. The signals affected had been behaving strangely for some time, but not enough to pin down a real problem.
- 1980s - Valley Heights train collisionValley Heights train collisionThe Valley Heights train collision was an accident on the Western Railway line of New South Wales at Valley Heights.- Overview :The collision was between a moving empty wheat train and the previous empty coal train which was stationary in Valley Heights station. The collision took place in the...
- electrician wrongly replace out clear glass lenses with coloured glass causing false colour with reflected sunlight.
- 1980s - Southern Region of BRBritish RailBritish Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...
- driver of stationary train sees signal ahead go to green, while train ahead still on line. Track circuitTrack circuitA track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signals.- Principles and operation :...
wiring fault somewhat like Clapham Junction rail crashClapham Junction rail crashThe Clapham Junction rail crash was a serious railway accident involving two collisions between three commuter trains at 08:10 on the morning of Monday, 12 December 1988....
. Alerts signalman, no accident.
- 1990 - Cowan rail disaster, which occurred when sand on the rails insulated the wheels from the rails, causing a failure to shunt that allowed a trailing block signal to improperly display a clear aspect, resulting in a rear end collision.
- 2005 - Deelfontein rail crashDeelfontein rail crashThe Deelfontein rail crash was a head-on collision when the Shosholoza Meyl Trans Karoo express hit the stationary Blue Train at a crossing loop at Deelfontein in South Africa in October 2005.Although there were some serious injuries, there was no loss of life...
- solderSolderSolder is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece.Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of . It is commonly used in electronics and...
splatter bridges a relayRelayA relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
contact. Most testing is done with the relays unplugged which would not detect the splatter, while the solder splatter is likely to lead to a difficult to trace phantom problem.
- 2009 - Ft Totten crash Washington DC MetroWashington MetroThe Washington Metro, commonly called Metro, and unofficially Metrorail, is the rapid transit system in Washington, D.C., United States, and its surrounding suburbs. It is administered by the Washington Metropolitan Area Transit Authority , which also operates Metrobus service under the Metro name...
(WMATA). An inbound Red Line train stopped short of Ft. Totten station; the following train failed to stop and impacted at ~42 mph. Nine dead, 80 injured. Preliminary NTSB reports are that the AC track circuit transmitter was breaking into parasitic oscillation, and that coupled across the rack cabinet to the receiver.
False alarms
Railway authorities usually give the drivers and signalmen the benefit of the doubt and investigate whether a wrong-side failure is the cause of the accident. This occurred with the Hinton train collisionHinton train collision
The Hinton train collision was a railway accident that occurred on February 8, 1986. Twenty-three people were killed in a collision between a Canadian National Railway freight train and a Via Rail passenger train. It was the most lethal Canadian rail disaster since the Dugald accident of 1947...
, but investigations soon showed that a wrong-side failure was not the cause.
The 2008 Chatsworth train collision
2008 Chatsworth train collision
The Chatsworth train collision occurred at 16:22 PDT on Friday September 12, 2008, when a Union Pacific freight train and a Metrolink commuter train collided head-on in the Chatsworth district of Los Angeles, California, in the United States...
was determined to be human error, not wrong side failure as a few initially said.
Wrong-side failures to be reported
In the United States there is a rule that wrong-side failures are to be reported to the Federal Railroad AdministrationFederal Railroad Administration
The Federal Railroad Administration is an agency in the United States Department of Transportation. The agency was created by the Department of Transportation Act of 1966...
.