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. ^[1]

1 Overview
2 Continuous and intermittent ATP
3 Eurobalise
4 Accidents and ATP
5 GSM-R
6 See also
7 References

[edit] Overview

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 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 BR 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 £1bn) was balked at by the Conservative government, who were preparing the company for privatisation.

All 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.

ATP is given permitted speed and location information from the track via encoded balise(s), encoded track circuit or more recently via radio.

In TfLs 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 since the modernisation of the line in 1996.

[edit] 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.

The Eurobalise is an attempt to set a standard for ATP across Europe where balises and on train equipment made by any manufacturer work together with each other.

[edit] Eurobalise

Eurobalise is the common specification for an ATP system able to go anywhere, and overcome the multiplicity of non-compatible designs currently in use. Any manufacturer can make the balises and the train board equipment.

[edit] Accidents and ATP

[edit] Accidents preventable by ATP

Salisbury rail crash - 1906 - Overspeed through sharp curve through station. Twenty-eight killed.^{[citation needed]}
Morpeth rail crashes - 1969 etc. - Overspeed through sharp curve.^{[citation needed]}

Malbone Street Wreck - 1918 - too fast around sharp curve - 93 killed^{[citation needed]}
Harmelen train disaster - 1962 - SPAD in fog causes collision - 91 killed.^{[citation needed]}
Violet Town railway disaster - 1969 - collapsed driver overruns crossing loop and collides with opposing train. Nine killed.^{[citation needed]}
Glenbrook train disaster - 1999 - too fast after Stop and Proceed.^{[citation needed]}
Waterfall train disaster - 2003 - too fast around very sharp curve.^{[citation needed]}
Ladbroke Grove rail crash - 1999 - inexperienced driver misread complicated signals, passes red signal and causes head-on collision.^{[citation needed]}
Hines Hill train collision - 1996 - driver misjudges end of crossing loop during simultaneous cross with opposing train. Two killed.^{[citation needed]}
Seven Hills, Blacktown and Concord West - drivers take turnouts at too high a speed, causing minor injuries to passengers.^{[citation needed]}
Amagasaki rail crash - 2005 - Overspeed through sharp curve. 107 killed, 555 injured. ^[2]

[edit] 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.^{[citation needed]}
Cowan rail crash - 1990 - wrong-side failure - caused by sand on the rails.^{[citation needed]}
Bruehl train disaster - 2000 - too fast through turnout during single-line working and degraded operations.^{[citation needed]}

[edit] 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.^{[citation needed]}
- 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 or forgot to apply that secondary brake.^{[citation needed]}