Signal passed at danger

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Two-aspect signal at danger (stop) in the United Kingdom

A signal passed at danger (S.P.A.D.), known in the United States as a stop signal overrun[1] and in Canada as passing a stop signal,[2]:75 is an event on a railway where a train passes a stop signal without authority.[3] In the United States and Canada, this may be known colloquially as running a red,[4] though this idiom principally refers to automobiles passing red traffic signals.[5][6]

The name derives from red colour light signals and horizontal semaphore signals in the United Kingdom, which are said to be at danger when they indicate that trains must stop (also known as the signal being on). This terminology is not used in North America where not all red signals indicate stop.[2]:72 In the U.K., the alternative description signal passed at red (S.P.A.R.) is used where a signal changes to red in front of a train due to either a technical fault or in an emergency, such that the train is unable to stop before passing the signal despite being driven correctly.


Because of its high inertia, it takes a considerable distance to stop a train, and incidents of this type often involve a slight or very slight overrun of the signal, at low speed, because the driver has braked too late, often after sighting the signal too late.

In some situations, however, the driver is unaware that they have passed a signal at danger and so continues until a collision occurs, as in the Ladbroke Grove rail crash. In such cases it is up to the safety system (where fitted) to apply the brakes, or for the signaller to alert the driver.

Some of the causes are:


Automatic train protection[edit]

Automatic train protection (ATP) 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 will also take into account the individual train characteristics such as brake performance. Thus, the ATP determines when brakes should be applied in order to stop the train before getting to the danger point. In the UK, only a small percentage of trains (First Great Western and Chiltern Railways) are fitted with this equipment.

Driver's reminder appliance[edit]

The DRA is an inhibiting switch located on the driver's desk of United Kingdom passenger trains designed specifically to prevent 'starting away SPADs'. The driver is required to operate the DRA whenever the train is brought to a stand,[10] either after passing a signal displaying caution or at a signal displaying danger.

Once applied, the DRA displays a red light and prevents traction power from being taken.

Collision prevention systems[edit]

Whilst the ideal safety system would prevent a SPAD from occurring, most equipment in current use does not stop the train before it has passed the Danger signal. However, provided that the train stops within the designated overlap beyond that signal, a collision should not occur.

Train stops[edit]

On the London Underground (for example), mechanical train stops are fitted beside the track at signals to stop a train, should an S.P.A.D occur.

Train stops are also installed on main line railways in places where tripcock equipped trains run in extensive tunnels, such as the on the Northern City Line where the Automatic warning system and Train Protection & Warning System are not fitted.

Train Protection & Warning System[edit]

On the UK mainline, TPWS consists of an on-board receiver/timer connected to the emergency braking system of a train, and radio frequency transmitter loops located on the track. The 'Overspeed Sensor System' pair of loops is located on the approach to the signal, and will activate the train's emergency brake if it approaches faster than the 'trigger speed' when the signal is at danger. The 'Train Stop System' pair of loops is located at the signal, and will activate the emergency brake if the train passes over them at any speed when the signal is at danger.

TPWS has proved to be an effective system in the UK,[citation needed] and has prevented several significant collisions.[citation needed] However, its deployment is not universal; only those signals where the risk of collision is considered to be significant are fitted with it.

Flank protection[edit]

At certain junctions, especially where if the signal protecting the junction was passed at danger a side collision is likely to result, then flank protection[11] may be used. Derailers and/or facing points beyond the signal protecting the junction will be set in such a position to allow a safe overlap if the signal was passed without authority. This effectively removes the chance of a side-impact collision as the train would be diverted in a parallel path to the approaching train.

SPAD indicators[edit]

SPAD indicator

Prior to the introduction of TPWS in the UK, "SPAD indicators" were introduced at 'high risk' locations (for example: the entry to a single track section of line). Consisting of three red lamps, they are placed beyond the protecting stop signal and are normally unlit. If a driver passes the signal at 'danger', the top and bottom lamps flash red and the centre lamp is lit continuously. Whenever a SPAD indicator activates, all drivers who observe it are required to stop immediately, even if they can see that the signal pertaining to their own train is showing a proceed aspect. Since the introduction of TPWS, provision of new SPAD indicators has become less common.

UK acronyms: SPAD / SPAR[edit]

In the UK, incidents where a signal is passed at danger without authority are categorised according to principal cause. A SPAD is where the train proceeds beyond its authorised movement to an unauthorised movement. Other types are categorised as SPAR ("signal passed at red").

Prior to December 2012,[12] the term "SPAD" applied to all such incidents, with a letter specifying cause.

  • A SPAD (formerly Category A SPAD) is where the train proceeds beyond its authorised movement to an unauthorised movement.[12]
  • A Technical SPAR (formerly Category B SPAD) is where the signal reverted to danger in front of the train due to an equipment failure or signaller error and the train was unable to stop before passing the signal.
  • A Signaller SPAR (formerly Category C SPAD) is where the signal was replaced to danger in front of the train by the signaller in accordance with the rules and regulations and the train was unable to stop before passing the signal.
  • A Runaway SPAR (formerly Category D SPAD) is where an unattended train or vehicles not attached to a traction unit run away past a signal at danger. Note that where this was the fault of the driver, this will be classed as a SPAD.

SPADs arising on starting from stations - typically those informally termed 'ding-ding right-aways', where the driver has inadvertently acted on a guard or dispatcher's indication without reading the signal - can be classified further:

  • SAS SPAD – "Starting against signal" SPAD,[13] where the train was standing at a danger signal and the driver moved past it.
  • SOY SPAD – "Starting on yellow" SPAD,[13] where the train left on a caution signal and the driver did not appreciate that the next signal might be at danger.

Passing signals at danger – with authority[edit]

Signals form part of a complex system, and it is inevitable that faults may occur. They are designed to fail safe, so that when problems occur, the affected signal indicates danger (an example where this did not happen was the Clapham Junction rail crash due primarily to faulty wiring). To keep the network running, safety rules enable trains to pass signals that cannot be cleared to a proceed aspect. Provided that authority for the movement is obtained, a SPAD does not occur. There are two methods of obtaining that authority:[14]

Driver obtains signaller's authority to pass a signal at danger[edit]

Once the train has been brought to a stand at a signal which is at danger, the driver should attempt to contact the signaller. If the signal cannot be cleared then the driver must obtain the signaller's authority to pass it at danger. Methods for contacting the signaller may include GSM-R cab radio, signal post telephone or mobile phone.

The signaller can authorise a driver to pass a signal at danger when:[15]

  • The signal is defective or disconnected
  • The signal cannot be cleared because signalling or level crossing equipment has failed
  • The signal is to be passed at danger for shunting purposes
  • The signal cannot be cleared because a train or movement which has reversed is then required to start from beyond that signal
  • An electric train is to pass the signal protecting an isolated section and proceed towards the limiting point
  • A train has been accepted using restricted acceptance because the line is clear only up to the home signal of the next signal box and the section signal cannot be cleared
  • In an emergency, and then only when authorised by the signal box supervisor or Operations Control, so that a train carrying passengers can enter an occupied section to use a station platform
  • An engineering train is to move towards a possession, or leave a line under possession at an intermediate point
  • A train is to pass the signal protecting engineering work to gain access to a station where the train is required to start back, or a line under single line working, or a siding
  • The line is to be examined to check that it is clear
  • A train is to proceed at caution through an absolute block section from the signal box in rear when a failed train has been removed
  • A train is to enter the section after a train or vehicle that has proceeded without authority has been removed, or the front portion of a divided train has passed through the section
  • A train is to enter the section to assist a failed train, evacuate passengers from a failed train, remove a portion of a divided train, or remove a train or vehicles that have proceeded without authority
  • Single line working applies
  • Working by pilotman or modified working applies

The driver and signaller must come to a clear understanding, and ensure they agree about how it is to be done. In the UK the signaller tells the driver of a specific train to pass a specific signal at danger, proceed with caution and travel at a speed that enables him to stop short of any obstruction, and then obey all other signals. If the signal is fitted with TPWS, the driver resets the Driver Reminder Appliance, pushes the TPWS Trainstop Override button in the cab, and proceeds cautiously through the section. If the train reaches the next signal without finding an obstruction, they must obey its aspect, at which point they can revert to normal working.

Driver passes a signal at danger under his own authority[edit]

If contact with the signaller cannot be made then the driver must not move the train, unless it is standing at one of the following signals:

After passing a signal at danger under his own authority, the driver must stop at the next signal (even if it is showing a proceed aspect) and inform the signaller of what they have done.

Accidents involving a signal passed at danger without authority[edit]

Accidents following a signal passed at danger with authority[edit]

Whenever a signal is passed at danger the driver is required to "proceed with caution, stop short of any obstructions, and drive at speed that will enable you to stop within the distance which you can see to be clear". Failure to do this has caused the following collisions:

Accidents where the signaller incorrectly authorised a driver to pass a signal at danger[edit]

Except where permissive working is in use, interlocking usually prevents a train from being signalled into a section that is already occupied. When operational needs require it, this can be overridden, and provided it is carried out in accordance with the rules this is a safe practice. However, failure to follow protocol can result in a collision:

See also[edit]

  • Ding-ding, and away, British slang for a guard incorrectly giving permission to a driver to start away from a platform against a red signal.


  1. ^ Multer, Jordan; Safar, Hadar; Roth, Emilie; France, Megan (June 2019). Why do Passenger Trains Pass Stop Signals - A Systems View (PDF) (Report). Washington, DC: Federal Railroad Administration. DOT/FRA/ORD-19/19. Archived (PDF) from the original on 2021-05-18. Retrieved 2021-05-18.
  2. ^ a b "Canadian Rail Operating Rules" (PDF). Transport Canada. 2020-04-24. Retrieved 2021-05-18.
  3. ^ "Signals Passed at Danger". Office of Rail and Road. Retrieved 2018-05-12.
  4. ^ a b Hersman, Deborah. "Texting: Tomorrow's Unacceptable Behavior". National Transportation Safety Board. Archived from the original on 2017-02-15. Retrieved 2016-09-11.
  5. ^ McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. The McGraw-Hill Companies, Inc. 2002.
  6. ^ Farlex Dictionary of Idioms. 2015. Retrieved 2021-05-18.
  7. ^ a b c "Articles" (PDF).
  8. ^ "Driver fatigue caused two Reading SPADs, says RAIB report". Rail Magazine. Vol. 812. 26 October – 8 November 2016. p. 23.
  9. ^ "Managing the risk from fatigue" (PDF). RSSB. Rail Safety and Standards Board. Retrieved 2016-11-21.
  10. ^ "Online Rulebook – Module TW1 – Section 10.3" (PDF). RSSB. Archived from the original (PDF) on 2011-09-29. Retrieved 2010-05-16.
  11. ^ "Railway Group Standards: Provision of Overlaps, Flank Protection & Trapping" (PDF). RGS. Retrieved 2011-02-18.
  12. ^ a b "Archived copy" (PDF). Archived from the original (PDF) on 2013-11-12. Retrieved 2013-11-12.CS1 maint: archived copy as title (link)
  13. ^ a b "Professional Driving Policy - a Freedom of Information request to East Coast Main Line Company Limited". WhatDoTheyKnow. January 27, 2015.
  14. ^ "Online Rulebook – Module S5 – Section 1.1 "Signaller's authority"" (PDF). RSSB. Archived from the original (PDF) on 2011-09-29. Retrieved 2016-03-04.
  15. ^ "Online Rulebook – Module S5 – Section 1 "When a signal can be passed at danger"" (PDF). RSSB. Archived from the original (PDF) on 2011-09-29. Retrieved 2017-06-18.
  16. ^ National Transportation Safety Board (January 21, 2010). "NTSB determines engineer's failure to observe and respond to red signal caused 2008 Chatsworth accident; recorders in cabs recommended" (Press release). Archived from the original on February 10, 2010. Retrieved January 23, 2010.
  17. ^ National Transportation Safety Board (June 18, 2013), NTSB Head-On Collision of Two Union Pacific Railroad Freight Trains Near Goodwell, Oklahoma June 24, 2012 (PDF), retrieved November 24, 2013
  18. ^ Clock, Nine O' (August 4, 2014). "Rail accident at entry point of Cotesti station of the Galati Regional".
  19. ^ Neves, Sofia (2020-08-01). "Erro humano causou acidente com Alfa Pendular em Soure. Operadores da máquina passaram o sinal vermelho" [Human error caused Alfa Pendular crash in Soure. [Maintenance] vehicle drivers passed signal at danger]. Público (in Portuguese). Retrieved 2021-04-13.

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