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London train crash Friday, 8 October, 1999, 13:29 GMT 14:29 UK
How the safety systems work
train at red signals
All trains have safety systems fitted
One of the key questions surrounding the west London train crash is whether better warning or automatic braking systems would have prevented the accident.

All trains are fitted with a warning system designed to alert drivers about to go through a red light.

London Train Crash
Some trains - although only a very small percentage of the entire train network - are fitted with systems which physically prevent them from going through red lights by triggering the brakes.

Approximately 600 trains last year, however, still ran through red lights.

Train Protection Warning System

The Train Protection Warning System (TPWS) is to be introduced across the whole rail network before 2004, replacing AWS.

The Health and Safety Executive said that TPWS would have prevented the west London crash.

It works along similar lines to ATP (below), except to the dismay of safety campaigners, it does not work on trains travelling at more than 70mph.

Deputy Prime Minister John Prescott was quoted in August as saying that the Health and Safety Commission believed TPWS would have prevented every accident caused by going through a red light since Clapham.

The cost of installing TPWS has been estimated at 150m-200m - at least six times cheaper than ATP. A total of 100m will be paid for by Railtrack, and the rest by the government.

Automatic Warning System

The Automatic Warning System (AWS) activates as the driver passes through signals. It is basically an auditory warning system, with a visual display reminder.

If he or she passes through a green signal, a bell goes off in the cab and no action has to be taken.

However, if the signal is any colour other than green, a claxon goes off.

Signals other than green in built up areas tend to be yellow, double yellow and red.

Double yellow alerts the driver that the following signal will be yellow, which in turn indicates that the following signal will be red. They tend to be placed about 1000 yards apart.

If the claxon goes off, the driver has a few seconds to acknowledge it by pressing a button. If he or she does not acknowledge, the brakes are applied automatically.

And if the driver acknowledges the warning horn, a black circle on the display lights up with yellow segments. This is known to drivers as "the sunflower".

The sunflower is a visual reminder to drivers that they have acknowledged going through a signal other than green, and take must take responsbility for taking appropriate action.

The driver in the Southall rail crash, where seven people died, would normally have had two warnings that he was approaching a red signal, but in that case the AWS was not working.

Automatic Train Protection

Automatic Train Protection (ATP) automatically stops a train going through danger signals.

Computerised equipment is installed in both the train and at key points along the track. The design should eliminate human error from SPADS (signals passed at danger) incidents.

The system is designed to stop trains travelling at up to 200mph from going through danger signals.

In addition, monitoring devices between tracks register the train's speed and activate its brakes if it is going too fast.

It is already operational on the Chiltern and Great Western lines, and its main functions were scheduled to be installed on the West Coast Main Line.

Some experts have said that ATP would have prevented two fatal rail crashes - one at Purley in 1989, and the other at Cowden in Kent in 1994.

southall rail crash
The inquiry into the Southall rail crash recommended ATP
The Hidden inquiry into the 1988 Clapham Rail crash, which claimed 35 lives, recommended that ATP should be introduced across the country's entire rail network.

The cost of installing ATP, however - estimated variously at 1-2bn - ruled out nationwide implementation.

Ironically, the stretch of line on which the west London crash happened is one of the few in the country where ATP is used.

The Great Western train was fitted with it, which, if it was working, would have prevented the train from running through a danger signal. The Thames turbo unit did not have ATP, but its AWS should have been operational.

Links to more London train crash stories are at the foot of the page.

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Links to more London train crash stories

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