Automatic train protection

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Automatic train protection (ATP) in Great Britain refers to either of two implementations of a train protection system installed in some trains in order to help prevent collisions through a driver's failure to observe a signal or speed restriction. Note that ATP can also refer to automatic train protection systems in general, as implemented in other parts of Europe and elsewhere.[citation needed]

Dead man's switch

The earliest safety device was the dead man's switch, which requires no track-side equipment.[citation needed]


This system uses a target speed indication and audible warnings to warn the train driver if they are likely to exceed a speed profile that will cause the train to pass a red (danger) signal or exceed a speed restriction. The system will apply the brakes if the driver fails to respond to these warnings. The system takes into account the speed and position of the train relative to the end of its "movement authority" in issuing the warnings and applying the brakes.

By the 1980s, microprocessors had developed sufficiently for British Rail to carry out pilot trials on existing European "off the shelf" ATP – fitting part of the Great Western Main Line with the TBL1 system from ACEC and the Chiltern Main Line route with SELCAB a derivative of the German LZB system from Alcatel and GEC.

In the early 1990s, following the Clapham Junction rail crash in December 1988, and two other fatal accidents in early 1989 caused by SPADs, British Rail was keen to implement the ATP system across the entire British railway system. However, the cost (estimated at over £1 billion) was balked at by the Conservative government, whose priority was the privatization of the railways.

All of First Great Western's High Speed Trains (HSTs) are now fitted with ATP and are not allowed to carry passengers unless the system is functioning. This requirement is in response to the Ladbroke Grove rail crash. All Chiltern Railways Class 165, Class 168 and Class 172 trains are also fitted with ATP. Also, all of Heathrow Express Class 332 trains and Heathrow Connect's Class 360/2 trains are fitted with this system.

ATP is given permitted speed and location information from the track via encoded balises, encoded track circuits, or more recently via radio signals.

In Transport for London's plans to modernise the London Underground network, all lines would be equipped with ATP, replacing the current train stop system, a mechanical system which currently prevents SPADs and collisions, but only after the train has passed the signal at danger. Timed signals are sometimes used, where a train has to spend a certain amount of time in a "berthing track circuit" before the signal can be cleared. The Central line is already equipped with ATP, installed as part of the modernisation of the line in 1995-1997.

Continuous and intermittent ATP

ATP systems may be broadly grouped as continuous and intermittent. With continuous ATP, a cable is laid between the rails for the full length of the block section. The rails themselves may also be used as the cable whereby the track talks to the train. With intermittent ATP, beacons called balises are mounted between the rails on the approach to signals, and perhaps at a few other locations.

ERTMS is an attempt to set a standard for Mainline ATP across Europe where balises, GSM-R Radio and on train equipment made by any manufacturer (who are part of the working group) work together with each other. This is achieved by carefully agreeing the functional specification of the system and the format and transmission methods of data across the air gap, both transponder and radio (GSM-R is the most common system in use).

Accidents and ATP

Accidents preventable by ATP

Accidents not preventable by ATP

Accidents reducible by ATP

  • France In the Gare de Lyon train accident in Paris in 1988, a brake failure was the prime cause of the accident. However a more modern ATP system, if fitted, might have reduced the intensity of the collision in two ways:
    • First, the onboard ATP equipment may have detected the excessive speed of the train sooner than the driver did.[citation needed]
    • Second, the ATP system presumably would have applied a secondary backup brake system, even though this might have "risked" flat wheels. Apparently, the driver failed to apply or forgot the existence of this secondary brake.[8] This led to a change in driver training, as some new drivers were told never to use this second system.

See also


  2. Japanese train crash kills dozens
  3. Steinhauer, Jennifer; Cieply, Michael (14 September 2008). "Rail Line Says Train Ran Signal; Death Toll at 25". The New York Times. Retrieved 31 March 2010.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. Sicherungssystem fehlt auf der Unglücksstrecke
  6. "Train derailment, 7/12/2014, Kaloyanovets, Bulgaria (Bulgaria)". European Railway Agency. Retrieved 23 November 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  7. "Системата за сигурност на железниците е причинила трагедията в Калояновец". Retrieved 23 November 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  8. "Runaway Train". Seconds from Disaster. Season 2. Episode 11. 2005-11-01. National Geographic Channel.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>