Signal passed at danger

Two-aspect signal at danger

A signal passed at danger (SPAD) in railway terminology of many countries, including Australia and the UK (where it is also known as either a SPAD or SPAR), occurs when a train passes a stop signal without authority to do so.[1] The United States's National Transportation Safety Board (NTSB), which investigates railway accidents in that country, typically terms this as running a red signal.[2]

Causes

Because it takes a considerable distance to bring a train to a stand, many signals are passed at danger at low speed where the driver has applied the brake too late. Often this occurs when the signal at danger cannot be clearly seen until it is closer than the braking distance of the train. It can also be due to:

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 this instance, it is up to the safety system (where fitted) to apply the brakes, or for the signaller to alert the driver.

Prevention

Automatic train protection

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 beyond 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

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,[6] 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

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

On the London Underground (for example), mechanical train stops are fitted beside the track at signals to stop a train, should a SPAD 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

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, and has prevented several significant collisions. 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

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[7] 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

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.

Signal passed at danger in the United Kingdom; Terminology and procedures

Acronyms: SPADs and SPARs

Prior to December 2012,[8] the term "SPAD" applied to all incidents where a signal was passed at danger without authority, and a letter was used to specify the principal cause.

Now the term SPAD is only used for what were previously category A SPADs and a new term, SPAR (Signal Passed at Red) is used to describe the former category B, C and D incidents.

There are a number of ways that a train can pass a signal at danger without authority, and in the UK these fall into four basic categories:

  • A SPAD (previously Category A SPAD) is where the train proceeds beyond its authorised movement to an unauthorised movement.[8]
  • A Technical SPAR (Previously 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 (Previously 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 (Previously Category D SPAD) is where an unattended train or vehicles not attached to a traction unit run away past a signal at danger.

Some SPADs can be defined as;

  • SAS SPAD – "Starting against signal" SPAD,[9] where the train was standing at a danger signal and the driver moved past it.
  • SOY SPAD – "Starting on yellow" SPAD,[9] where the train left on a caution signal and the driver did not appreciate that the next signal would be at danger.

Passing signals at danger – with authority

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:[10]

1) Driver obtains signaller's authority to pass a signal at danger

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 cab radio (NRN, Cab Secure or GSM-R), signal post telephone or mobile phone.

The signaller can authorise a driver to pass a signal at danger when:[11]

  • 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, he must obey its aspect, at which point he can revert to normal working.

2) Driver passes a signal at danger under his own authority

If contact with the signaller cannot be made then the driver must not move his 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 he has done.

Accidents involving a signal passed at danger without authority

This list is incomplete; you can help by expanding it.

Accidents following a signal passed at danger with authority

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

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:

Location Time Fatalities/Injured Notes References
RomaniaBucerdea, Romaina 1968 Crash?
United KingdomSeer Green, United Kingdom 1981 4 dead, 5 injured Empty train stopped due to branch that blocked the line because of carrying too much snow. The signalman believed the empty train had continued its journey and thus cleared the train after it - a passenger train - to pass the signal at danger. The driver of the passenger train saw the empty train too late and the train ran into it(Main article)
IndonesiaJakarta, Indonesia wrong date? (Crash)
GermanyBad Aibling, Germany 2016 12 died, 85 injured, of which 24 seriously The signalman, while playing games, cleared first one train on the track, then another one to pass the signal at danger. Realizing his mistake, he tried to contact the conductors via radio, but used the wrong radio number. The trains were too fast to come to a halt in time and crashed into each other (Bad Aibling)

See also

  • 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.

References

  1. ↑ "Signals Passed at Danger". ORR.gov.uk. Office of Rail and Road. Retrieved 2018-05-12.
  2. 1 2 Hersman, Deborah. "Texting: Tomorrow's Unacceptable Behavior". App.NTSB.gov. National Transportation Safety Board. Retrieved 2016-09-11.
  3. 1 2 3 Human Reliability study - Getting at the underlying causes of SPADs
  4. ↑ "Driver fatigue caused two Reading SPADs, says RAIB report". Rail Magazine. Vol. 812. 26 October – 8 November 2016. p. 23.
  5. ↑ "Managing the risk from fatigue" (PDF). RSSB. Rail Safety and Standards Board. Retrieved 2016-11-21.
  6. ↑ "Online Rulebook – Module TW1 – Section 10.3" (PDF). RSSB. Archived from the original (pdf) on 2011-09-29. Retrieved 2010-05-16.
  7. ↑ "Railway Group Standards: Provision of Overlaps, Flank Protection & Trapping" (PDF). RGS. Retrieved 2011-02-18.
  8. 1 2 "Archived copy" (PDF). Archived from the original (PDF) on 2013-11-12. Retrieved 2013-11-12.
  9. 1 2 EC Professional Driving Policy
  10. ↑ "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.
  11. ↑ "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.
  12. ↑ 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.
  13. ↑ 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
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