Automatic Train Protection
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.
Dead man's switch
The earliest safety device was the dead man's switch, which requires no track-side equipment.
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 and Class 168 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 balise(s), encoded track circuit or more recently via radio.
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. The Central Line is already equipped with ATP, installed with the modernisation of the line in 1996.
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 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
- Russell Hill Subway Crash - 1995 - Driver passed two signals at danger, resulting in a collision between two subway trains. The line was equipped with train stops, but they were installed incorrectly and thus did not function.
- Hines Hill train collision - 1996 - driver misjudges end of crossing loop during simultaneous cross with opposing train. Two killed.
- Watford rail crash - 1996 - Signal passed at danger resulting in collision with coaching stock. One killed.
- Southall rail crash - 1997 - Signal passed at danger, resulting in a collision between a passenger train and a freight train crossing the track in front of it.
- Ladbroke Grove rail crash - 1999 - inexperienced driver misread complicated signals, passes red signal and causes head-on collision.
- Glenbrook train disaster - 1999 - too fast after Stop and Proceed.
- Waterfall train disaster - 2003 - too fast around very sharp curve after driver suffered a heart attack.
- Seven Hills, Blacktown and Concord West - drivers take turnout at too high a speed, causing minor injuries to passengers.
- 17 September 2005 Too fast through turnouts between Joliet and Chicago.
- Amagasaki rail crash - 2005 - Overspeed through sharp curve. 107 killed, 555 injured.
- Chatsworth train collision - 2008 - driver of commuter train passes red signal and collides head-on with freight train - 25 killed 
- Hordorf rail crash - 2011 - Signal passed at danger resulting in collision between a passenger train and a freight train - 10 dead, 23 injured.
Accidents not preventable by ATP
- Clapham Junction rail crash - 1988 - wrong-side failure - both signal and balise would have shown false green lights. 35 killed, 100 plus injured.
- Cowan rail crash - 1990 - wrong-side failure - caused by sand on the rails.
- Clementi train collision - 1993 - oil spillage on track, may have interfered with normal ATP operation on the 12 trains that arrived at Clementi MRT Station in the early morning since the oil have come into contact with the ATP power system fixed into the rails. The ATP system in question is continuous ATP, which is still used on the North South MRT Line and the East West MRT Line. 156 injuries, no deaths.
- Bruehl train disaster - 2000 - too fast through turnout during single-line working and degraded operations.
Accidents reducible by ATP
- 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:
- Firstly, the on board ATP equipment may have detected the excessive speed of the train sooner than the driver did.
- Secondly, 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.
- Dead man's switch
- Automatic Warning System
- Train Protection & Warning System
- Train protection system
- Train warning system - an Indian system 
- Automatische treinbeïnvloeding (ATB) – a Dutch system which would have prevented the Harmelen train disaster.
- European Train Control System (ETCS)
- Anti Collision Device
- Lists of rail accidents
- IRSE News
- http://news.bbc.co.uk/1/hi/world/asia-pacific/4480031.stm Japanese train crash kills dozens
- 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.
- http://www.spiegel.de/panorama/zugunglueck-in-sachsen-anhalt-sicherungssystem-fehlt-auf-der-ungluecksstrecke-a-742525.html Sicherungssystem fehlt auf der Unglücksstrecke
- "Runaway Train". Seconds from Disaster. Season 2. Episode 11. 2005-11-01. National Geographic Channel. http://channel.nationalgeographic.com/series/seconds-from-disaster/2389/Overview.
- Track & Signal 2008/4 p87