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Thursday, 28 September, 2000, 12:48 GMT 13:48 UK
How the safety systems work
train at red signals
All trains have safety systems fitted
All trains are fitted with safety systems. Currently most have a claxon warning system designed to alert drivers who are about to go through a red light.

But as a result of the fatal Paddington, Southall and Clapham rail crashes this simple system is widely considered to be inadequate and outdated.

An increasing number of trains are being fitted with a system which physically prevents the train from going through a red light by triggering the brakes. The government is committed to expanding this type of warning system across the network by the end of 2003.

However, there are two types of train protection system in this category, and there has been much debate over which should be introduced across the UK.

The two systems at the centre of the controversy are Automatic Train Protection (ATP) and the less sophisticated Train Protection Warning System (TPWS).

The Hidden Inquiry into the Clapham train crash in 1988 and the Paddington train crash survivors both favour ATP. It is the more expensive system but is considered to be fail-safe.

A report by Sir David Davies, President of the Royal Academy of Engineering, after the Paddington crash recommended the cheaper TPWS.

Here is a guide to differences between the main safety systems.

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 responsibility 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.

The situation in the case of the Paddington crash is not entirely clear, but it is thought that a faulty track could have triggered the wrong noise in the cabin of the driver of the Thames train leading him to believe he had been given a green signal instead of a red one.

It was revealed at the inquiry that Michael Stodder, the driver of the Thames Train, had not received training in red signal awareness.

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

The Health and Safety Executive has 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.

So far Railtrack and the government have invested 140m in the system. Railtrack says it will prevent 70% of accidents. The cost of installing TPWS is at least six times cheaper than ATP.

Many of the survivors of the Southall and Paddington disasters are concerned that the government and rail companies are pre-empting the Paddington inquiry and the joint inquiry into train safety by pushing ahead with implementing TPWS.

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.

However ATP is currently being limited to four high speed lines; the East and West Coast main lines, Great Western line and the Channel Tunnel rail link.

The cost of installing ATP, estimated variously at 1-2bn - has appeared to rule out nationwide implementation.

Ironically, the stretch of line on which the Paddington 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 had been working, would have prevented the train from running through a danger signal.

The Thames turbo unit did not have ATP although it was being tested on the lines out of Paddington.

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