Signal passed at danger


Signal passed at danger

Signal passed at danger (SPAD), in railway terminology, describes an event where a train has run beyond its allocated signal block without authority, as indicated by a lineside signal showing danger (typically a red light). It is a term primarily used within the British Railway Industry, although it can be applied worldwide.

Causes

Most SPADs occur at low speed where braking distance has been misjudged, and the train can subsequently be stopped within a safety overlap area, either by the engineer/driver or by an automatic application of the emergency brakes by a safety system, such as the Train Protection & Warning System (TPWS). In some situations where a signal cannot be seen due to obstruction, sufficient braking may not have been achieved, and the train will continue to run a significant distance beyond the danger signal. Such an incident was determined as the main cause of the Ladbroke Grove rail crash at a time when TPWS was not in operation.

Reasons that drivers do not see red signals include: fog, falling snow, badly designed signal layouts, inattention and being distracted, signal light dim or dirty or lamp failure.

Almost all railways require a dim or dark signal to be treated as if it were displaying its most restrictive aspect, i.e. 'stop' for a stop signal or 'caution' for a distant signal. In most cases, the type of signal can be determined by a plate or coloured marking on the signal post. A somewhat related fault is when a semaphore signal's arm is stuck in the 'clear' position, e.g. by frost or snow.

Prevention

Train stops

On the London Underground (for example), train stops are fitted on the track to stop a train, should a driver cause a SPAD. Should a train be stopped under such circumstances, delays occur because the train's trip cock has to be reset, and a replacement driver found as the offending driver is not permitted to continue with the train. Train stops (and trip cock equipped trains) are also operated by the main line railways, in many places where extensive tunnel operation is carried out.

Automatic Train Protection

ATP (Automatic Train Protection) is a much more advanced form of Train Stop, which can regulate the speed of trains in many more situations other than at a stop signal. ATP supervises speed restrictions and distance to danger points. An ATP does take into account individual train characteristics such as brake performance. Thus, the ATP determines when brakes should be applied in order to stop the train before getting beyond the danger point.

SPAD indicators

Prior to the introduction of Train Protection & Warning System (TPWS) in the UK, "SPAD indicators" were introduced at 'high risk' locations (for example: the entry to a single track section of line). These SPAD indicators are placed beyond the protecting stop signal and are normally unlit. Should a driver pass the signal at 'danger', a track circuit or treadle detects this and causes the SPAD indicator to flash red lights to warn the driver of his error. Since the introduction of TPWS, provision of new SPAD indicators has become less common.

Stop and proceed

Automatic signals may be passed at 'danger' in accordance with the rules. The driver must proceed with extreme care as there may be obstacles in the way. If the driver out of habit forgets to maintain a low speed, accidents such as the Glenbrook train disaster can occur.

Signals passed under these rules are not classified as SPADs. In general, this can only be done under the direction of a signalman, but rules vary greatly between countries and even systems with countries.

Accidents involving SPADs

* - Ais Gill disaster, 1913 (UK)
* - Potters Bar, 1946 (UK)
* - Harrow and Wealdstone rail crash, 1952 (UK)
* - Lewisham rail crash, 1957 (UK)
* - Dagenham East rail crash, 1958 (UK)
* - Harmelen train disaster, 1962 (Netherlands)
* - Violet Town, Victoria, 1969 (Australia)
* - Glasgow Bellgrove rail crash, 1989 (UK)
* - Purley station rail crash, 1989 (UK)
* - Newton rail crash, 1991 (UK) - also single lead junction
* - Norton Bridge rail crash, 1991 (UK)
* - Cowden rail crash, 1994 (UK)
* - Southall rail crash, 1997 (UK)
* - Beresfield, New South Wales, 1997 (Australia)
* - Winsford rail crash, 1999 (UK)
* - Ladbroke Grove rail crash, 1999 (UK) - a SPAD that led to dozens of deaths. Prompts TPWS.
* - Pécrot Rail Crash, 2001 (BE)
* - Arnhem rail crash - 2006 (Netherlands)
* - 2008 Chatsworth train collision (US) - Based on preliminary report by railway -- official cause pending.

References

* [http://www.hse.gov.uk/railways/spads.htm UK Health and Safety Exec] , Retrieved 8 March 2006.

External links

* [http://www.rail-reg.gov.uk/server/show/ConWebDoc.7788 Office of Rail Regulation]


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • signal — 1 / sIgnFl/ noun (C) 1 a sound or action that you make in order to give information to someone or tell them to do something: signal (for sb) to do sth: A bell began to ring, the 8 o clock signal to start work. | When he closes his book, it s a… …   Longman dictionary of contemporary English

  • Railway semaphore signal — One of the earliest forms of fixed railway signal is the semaphore. These signals display their different indications to train drivers by changing the angle of inclination of a pivoted arm . Semaphore signals were patented in the early 1840s by… …   Wikipedia

  • all-clear signal — signal that everything is OK, sign that the danger has passed, signal that the situation is safe …   English contemporary dictionary

  • Distress signal — Call for help redirects here. For the TV show, see Call for Help. A distress signal is an internationally recognized means for obtaining help. Distress signals take the form of or are commonly made by using radio signals, displaying a visually… …   Wikipedia

  • Alarm signal — In the field of animal communication, an alarm signal is an antipredator adaptation referring to various signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning conspecifics of… …   Wikipedia

  • List of rail accidents in the United Kingdom — This list is of railway accidents in Britain sorted chronologically. For a list sorted by death toll see List of British rail accidents by death toll. It does not include incidents that did not involve rolling stock, such as the King s Cross fire …   Wikipedia

  • Marden rail crash — Date and time 4 January 1969 at 20:42 Location Between Paddock Wood and Marden railway stations. Coordinates Approximately TQ 724 449 …   Wikipedia

  • UK railway signalling — The railway signalling systems used across the majority of the United Kingdom rail network use lineside signals to advise the driver of the status of the section of track ahead. Most lineside signals are in colour light form, but a significant… …   Wikipedia

  • Clayton Tunnel rail crash — The tunnel s north entrance Date and time 25 August 1861 : 0845 Location Clayton, West Sussex Rail line Brighton Ma …   Wikipedia

  • Invergowrie rail accident — NOTOC infobox UK rail accident title= Invergowrie rail accident date= 22 October 1979 location= Invergowrie, Scotland line = Glasgow to Aberdeen line cause= Signal passed at danger trains= 2 pax= deaths= 5 injuries= 51 The Invergowrie rail… …   Wikipedia