This article was reproduced with the kind permission
of the British Broadcasting Corporation ©
October 8, 1999 Published at 15:55 GMT 16:55 UK
Train accident at Ladbroke Grove Junction, 5 October 1999
First HSE interim report,
8 October 1999
2. At 8.11am on 5 October two trains collided 2 miles outside Paddington station, at Ladbroke Grove Junction. One was a Great Western High Speed Train (HST) running from Cheltenham Spa to Paddington, the other a Thames Train 3-car diesel unit going from Paddington to Bedwyn, in Wiltshire. 30 people are already confirmed as dead and many more are unaccounted for. There are also 160 injured, some critically, because of a rapid outbreak of fire in some of the HST carriages.
3. HSE's Railway Inspectorate (RI) is investigating the cause of the accident with the aim of answering three main questions:
4. The final report will take some time to complete but, as significant findings come to light, RI will make them public and will also take action where this is appropriate. This interim report sets out the initial findings from the first three days' worth of work.
5. Key points
Layout of the accident site
6. A greatly simplified diagram at Appendix 1 (for illustrative purposes only) shows the layout of the lines where the accident happened, which is also described in the following paragraphs. There are also some photographs showing the crash site. (The appendix and photographs referred to above will be made available shortly)
7. To the west of Ladbroke Grove Junction there are four running lines:
8. To the east of Ladbroke Grove Junction there are six bi-directional running lines identified as Lines 1 to 6. At the junction there are connections between the various lines.
9. The Up Main line becomes Line 2. There is a high-speed connection from the Up Main Line to Line 3 just to the east of the Up Main line signal SN120 for trains travelling towards Paddington. Further to the east there is a crossover between Line 3 and the Down Relief line. Further east still there is another crossover from Line 3 to the Up Main line and another crossover between the Up and Down Main lines which allows trains travelling towards Reading to cross from Line 3 to the Down Main line. Line 3 does not extend to the west of Ladbroke Grove Junction.
10. Access from Line 3 to either the Down Main or Down Relief lines, for trains travelling towards Reading, is controlled by signal SN109. The signal is located on a gantry which spans all six of the lines and which also carries signals for each of the other lines. The distance between signal SN120 on the Up Main line and Signal SN109 on Line 3 is some 700m.
The signalling system
11. The signalling at Paddington is controlled by a Solid State Interlocking (SSI) system located at the Slough Control Centre. The system also includes a computer-driven Automatic Route Setting (ARS) facility. ARS requests the SSI to set routes for trains in accordance with a pre-loaded timetable, instead of the signaller doing it manually.
On the morning of the collision the ARS was in use and the signaller at the Control Centre was visually monitoring the progress of trains, using VDU displays on the control desk. The routes set for the two trains
12. The 6.03 Cheltenham to Paddington train (train 1A09) was following an earlier train along the Up Main line towards Paddington. After the signals had turned back to red behind the previous train, they progressively turned back through yellow to double yellow and then green as the train proceeded - which is normal. Therefore, 1A09 was travelling on green signals a safe distance behind the previous train.
13. The ARS had set a route for the 08.06 Paddington to Bedwyn train (train 1K20) up to Signal SN109 on Line 3. The train on leaving Paddington Station had travelled on Line 4 and crossed on to Line 3 on the approach to SN109.
Signalling systems: RI's findings so far
14. On the morning of Tuesday 5 October Mr Alan Cooksey, Deputy Chief Inspector of Railways, went directly to the control centre at Slough where he confirmed with the signallers what they had observed from the signalling displays. He also oversaw the removal of the data recording tape from the SSI and the initial analysis of the information it contained.
Analysis of the SSI data
15. There are data tape records of:
16. While a high level of confidence can be gained from the analysis of the SSI data tapes, we cannot absolutely confirm that all of the signal equipment at the site did function in accordance with the instructions issued by the SSI until each piece of equipment from the site has been tested.
That work is in progress at the moment. In particular, we must be absolutely certain to ensure that although signal SN109 was required to be showing a stop (red) aspect and reported back to the SSI as doing so, that there is no possibility, however unlikely, that it was showing any other aspect.
What follows is the most likely sequence of events, based on present knowledge. RI's interpretation has now been confirmed by an additional independent report from W S Atkins.
17. The signaller who had been observing the progress of the trains on the VDU realised that train 1K20 had passed Signal SN109 and was heading towards the Up Main Line on which train 1A09 was approaching. He immediately changed signal SN120 on the Up Main Line to Danger.
However, by that time train 1A09 must have been very close to the signal and travelling at speed (which needs to be confirmed when analysis of the data recorder from the rear cab is to hand) and the collision occurred almost simultaneously.
18. Examination of the SSI data tape confirms that the route for train 1A09 had been requested by the ARS, the instructions were processed by the SSI, and the commands issued to the computer modules which control the signals and points for a route from the Up Main Line to Line 2 and Paddington Station.
The signal aspects displayed for 1A09 and its progress through the occupation and then clearing of the relevant track circuits were also confirmed from the data tapes.
19. The data tapes also confirm the ARS requesting the route up to Signal SN109, which was showing a red aspect, for train 1K20. Subject to the further tests outlined above, the likelihood is that train 1K20 therefore passed a red light. The data tapes show the progressive occupation of track circuits as train 1K20 passed signal SN109 and travelled some 700m into the path of train 1A09.
The other signals on the SN109 gantry
20. At the time train 1K20 approached Signal SN109 it appears that no other routes had been set which would have resulted in the other signals on the gantry showing any aspects other than red.
21. HSE has deployed two fire experts from the Health and Safety Laboratory to investigate the nature of the fire. They have made a survey of the fire damage where access has been possible to do this:
22. On this basis of what we know so far about the speed of train 1K20, the accident was preventable by the Train Protection Warning System (TPWS).
23. We have also made a videotaped reconstruction of 1K20's approach to signal SN109, which shows that there are issues relating to signal siting which need further investigation.
24. Further lines of enquiry for RI's investigation will include: