Signal passed at danger

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Two-aspect signal at danger

A signal passed at danger 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 NTSB, which investigates railway accidents in that country, typically terms this as running a red signal.[2]

Causes[edit]

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[edit]

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 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. 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,[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 avoidance[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 detection[edit]

There are two main forms of train detection;

  • Track circuits operate by use of an electric current flowing through one or both running lines. If a train is present the current will short-circuit the track through the axles and not reach the far end, de-energising a relay.
  • axle counters are placed at the beginning and end of a signal section, and are used to ensure that a train has passed through complete.

Occasionaly when the two main methods aren't suitable a mechanical treadle operated by the train wheels is used.

Train stops[edit]

Main article: Train stop

On the London Underground (for example), train stops are fitted on the track to stop a train, should a SPAD occur. When a train is stopped under such circumstances, delays occur because the train's trip cock has to be reset, and a replacement needs to be found as the 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 places where extensive tunnel operation is carried out, such as 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 trigger the train brakes if it approaches faster than the 'set speed' when the signal is at danger. The 'Train Stop System' pair of loops is located at the signal, and will trigger the brakes 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[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[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[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). These SPAD indicators are placed beyond the protecting stop signal and are normally unlit. Should a driver pass the signal at 'danger', some form of train detection, detects this and causes the SPAD indicator to flash red lights to warn the driver of the error. 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[edit]

Acronyms - SPADs and SPARs[edit]

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 didn't appreciate that the next signal would be at danger.

Passing signals at dangerwith 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;[10]

1) 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 Cab Radio (NRN, Cab Secure or GSM-R), Signal Post Telephone or Mobile phone.

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.[edit]

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[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.

References[edit]

  1. ^ "Office of Rail Regulation: Signals passed at danger". ORR. Retrieved 2011-02-17. 
  2. ^ a b Hersman, Deborah. "Texting: Tomorrow's Unacceptable Behavior". App.NTSB.gov. National Transportation Safety Board. Retrieved 2016-09-11. 
  3. ^ a b c 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. Retrieved 2010-05-16. 
  7. ^ "Railway Group Standards: Provision of Overlaps, Flank Protection & Trapping" (PDF). RGS. Retrieved 2011-02-18. 
  8. ^ a b http://www.rgsonline.co.uk/Railway_Group_Standards/Traffic%20Operation%20and%20Management/Railway%20Group%20Standards/GORT3119%20Iss%203.pdf
  9. ^ a b EC Professional Driving Policy
  10. ^ "Online Rulebook – Module S5 – Section 7" (pdf). RSSB. Retrieved 2016-03-04. 
  11. ^ 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). Retrieved January 23, 2010. 
  12. ^ 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 

External links[edit]