Wrong-side failure
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A wrong-side failure describes a failure condition in a piece of
railway signalling Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormou ...
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
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switch ...
that has to energize to show a
green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...
light. If a wire breaks, or the battery is drained, then the relay will de-energize and the signal will show a
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
light, which is
fail-safe In engineering, a fail-safe is a design feature or practice that in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent 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, also known as double cut, 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 (England) - signals frozen by
blizzard A blizzard is a severe snowstorm characterized by strong sustained winds and low visibility, lasting for a prolonged period of time—typically at least three or four hours. A ground blizzard is a weather condition where snow is not falling b ...
in 'clear' position (signal arm hidden in a slot in the post). * 1915 – Rockledge, Tennessee - Relocation of a Western Union telegraph line from old alignment to new alignment causes a false clear signal indication when the Western Union wire comes in contact with the signal wire for the automatic block signal at the south end of the siding at Rockledge. A southbound freight train departed Rockledge on the false clear indication and collided with a northbound passenger train that had entered the block at Tantallon on a proper clear indication two minutes before the freight train departed Rockledge. A contributing factor was that the tower operator at Rockledge only controlled the signals, the track switches being operated by the train crews themselves. * 1927 – Marrar (NSW, Australia) - lightning damage meant that the single line train tablet system incorrectly released two tablets simultaneously putting two trains on a collision course; fortunately they saw each other and were able to stop in time. * 1938 –
Charing Cross (Northern line) tube crash The Charing Cross (Northern line) tube crash occurred at 08:32 hours on 10 March 1938, when a Northern line train ran into the rear of a stationary train near Charing Cross (now Embankment) in London. Twelve people were slightly injured. The ...
(London) - signal linesman rewires a faulty signal incorrectly, so that it shows green too soon; two
Underground Underground most commonly refers to: * Subterranea (geography), the regions beneath the surface of the Earth Underground may also refer to: Places * The Underground (Boston), a music club in the Allston neighborhood of Boston * The Underground ...
trains collide as a result, injuring twelve. Also
Charing Cross (District line) tube crash The Charing Cross (District line) tube crash occurred on 17 May 1938 at about 09:55 hours, between Charing Cross (now Embankment) and Temple stations. Six people were killed when a Circle line service ran into the rear of a District line se ...
, signal linesman makes wiring error in cabin, two
Underground Underground most commonly refers to: * Subterranea (geography), the regions beneath the surface of the Earth Underground may also refer to: Places * The Underground (Boston), a music club in the Allston neighborhood of Boston * The Underground ...
trains collide, killing six. * 1953 – Sydenham Rail Disaster (NSW, Australia) - five killed * 1976 – Glenbrook, New South Wales (Australia) Automatic signal in rear of a stationary
EMU The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus ''Dromaius''. The 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 crash , symbol_location = gb , symbol = rail , image = Invergowrie rail station.jpg , borough = Invergowrie, Perth and Kinross , country = Scotland , coordinates = , grid_name ...
(Scotland) - signal was at "wrong" (i.e. indistinct indication) yet taken by driver to be a 'proceed' signal. * 1982 - Valley Heights train collision (NSW, Australia) - electrician wrongly replace out clear glass lenses with coloured glass causing false colour with reflected sunlight. * 1988 -
Clapham Junction rail crash The Clapham Junction railway crash occurred on the morning of 12 December 1988, when a crowded British Rail passenger train crashed into the rear of another train that had stopped at a signal just south of Clapham Junction railway station in L ...
(London) - single stray wire causes false green signal and collision killing 35. * 1990 - Cowan rail disaster (NSW, Australia), 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 (South Africa) -
solder Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...
splatter bridges a
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switch ...
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 – On March 26, two trains collided near Arévalo, Spain while engineers were testing a new signalling system. Lack of safeguards and testing on an active line led to the collision of two freight trains. One of the train drivers died. * 2009 – Ft Totten crash Washington DC Metro (WMATA). An inbound Red Line train stopped short of Ft. Totten station; the following train failed to stop and impacted at about . Nine dead, 80 injured. Preliminary NTSB reports were that the AC track circuit transmitter was breaking into parasitic oscillation, and that coupled across the rack cabinet to the receiver. * 2020 - On the Italian high speed rail network, maintenance workers during the night left a faulty point to the reverse position, but disconnected its network connection and its link to the safety signalling system (
ETCS The European Train Control System (ETCS) is the signalling and control component of the European Rail Traffic Management System (ERTMS). It is a replacement for legacy train protection systems and designed to replace the many incompatible s ...
L2); the first morning high speed train received a green signal to proceed at full speed and hit the point at , resulting in the
Livraga derailment The Livraga derailment is the first and only railway accident to date that ever happened on the Italian high speed rail network. It took place on 6 February 2020 when a high-speed train derailed at Livraga, Lombardy, Italy. Two people died and 31 we ...
which killed 2 and injured 31.


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 collision The Hinton train collision was a rail transport accident that occurred in Canada on 8 February 1986. Twenty-three people were killed in a collision between a Canadian National Railway freight train and a Via Rail passenger train called the '' S ...
, 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.


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 Administration The Federal Railroad Administration (FRA) is an agency in the United States Department of Transportation (DOT). The agency was created by the Department of Transportation Act of 1966. The purpose of the FRA is to promulgate and enforce rail saf ...
. Witnesses: Doomed train had green light - ''
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'', October 7, 2008.


See also

*
Lists of rail accidents This is the list of rail accident lists. Lists By year By type *By country * By death toll *Terrorist incidents See also * Classification of railway accidents * Derailment *Rail Transport * Train wreck A train wreck, train collision, tr ...


References

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External links


False proceedNotifiable incidents
Railway signalling