caravanman
Engineer
Folk might be interested to read the detailed report published today into the Salisbury rail collision a few months ago.
( Salisbury train crash: Major incident as two trains collide. )
The RAIB today have published their interim report on this accident. An extract can be found below:
( Salisbury train crash: Major incident as two trains collide. )
The RAIB today have published their interim report on this accident. An extract can be found below:
Summary
1 At around 18:43 hrs on 31 October 2021, train reporting number 1L53, the 17:20 hrs South Western Railway passenger service from London Waterloo to Honiton, collided with the side of train 1F30, the 17:08 hrs Great Western Railway passenger service from Portsmouth Harbour to Bristol Temple Meads. The collision took place at Salisbury Tunnel Junction, which is on the immediate approach to Fisherton tunnel, near Salisbury in Wiltshire.
2 The impact of the collision caused the front two coaches of train 1L53 and the rear two coaches of train 1F30 to derail. Both trains continued some distance into Fisherton tunnel following the collision, before they came to a stop. Thirteen passengers and one member of railway staff required treatment in hospital as a result of the accident, which also caused significant damage to the trains and railway infrastructure involved.
3 Train 1L53 approached Salisbury Tunnel Junction on the down main line. The movement of train 1F30 across the junction was being protected from trains approaching on this line by signal SY31, which was at danger (displaying a red aspect). Train 1L53 passed this signal, while it was at danger, by 191 metres, before colliding with train 1F30.
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The accident
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21 At 18:41:09 hrs, 1 minute and 47 seconds before the accident (timings in this section are taken from the train’s OTDR, adjusted to synchronise with the time recorded by the signalling system), the driver of train 1L53 shut off power and allowed the train to coast down the prevailing 1 in 169 gradient. Ten seconds later he acknowledged the AWS warning for signal SY29R, which was showing a double yellow preliminary caution aspect. At 18:42:03 hrs, around 1,600 metres after passing signal SY29R and with the train travelling at 86 mph (138 km/h) on level track, the driver made a step 2 brake application. This was in accordance with his usual practice and was done with the intention of being able to stop the train at signal SY31, which was at this point around 1,500 metres away. Although the train’s speed began to reduce, analysis of OTDR data shows that its wheels began to slide almost immediately after this brake application was made. The driver made a full-service brake application five seconds later and moved the brake controller to the emergency brake position after a further six seconds. The train’s wheel slip/slide prevention (WSP) system was active throughout this braking, but the train’s speed reduced only slowly.
22 As the train approached signal SY31, which remained at danger, the Train Protection and Warning System (TPWS) fitted to the train detected that it was travelling above the set speed of the overspeed sensor (OSS) system fitted on approach to the signal, 34.5 mph (55.5 km/h). The TPWS system therefore made an emergency brake demand. This had no effect on the degree of braking demanded, because the maximum available braking had already been applied by the driver.
23 Train 1F27 passed across and clear of Salisbury Tunnel Junction less than 40 seconds before train 1L53 arrived. Subsequently, the driver of train 1L53, which was still sliding and rapidly approaching signal SY31, saw train 1F30 appear from the left and move into the path of his train. Train 1F30 was at this point travelling at 20 mph (32 km/h).
24 At the point where the two trains collided, train 1L53 was travelling at between about 52 and 56 mph (84 and 90 km/h). Train 1L53 struck 1F30 on its right-hand side near the front of the fourth coach, as both trains crossed the junction and as 1F30 was entering Fisherton tunnel.
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Initial findings
Railhead condition
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36 The railhead was found to be contaminated throughout the areas surveyed with a black deposit. This deposit consisted of leaf material which had been crushed under the wheels of passing trains and which is often associated with low adhesion conditions. Analysis showed that many areas had a medium or heavy level of contamination, and that the thickness of the leaf deposit was relatively consistent through each of the areas surveyed. It is likely that the rails were wet at the time of the accident. Wet values of the coefficient of friction measured as part of the post-accident survey were found to be between 0.2 and 0.02, suggesting that there was low friction between the wheels and the railhead. The average rate of deceleration of train 1L53 suggests adhesion levels closer to the 0.02 value were prevalent at the time of the accident. Samples taken from the area around signal SY29 and between there and the junction showed that the deposits were smeared and flaky and typical of the sort of contamination layers which exist after train wheels have slid over them.
Train driving
37 OTDR data shows that train 1L53 was travelling within the permitted speed as the train approached Salisbury Tunnel Junction. RAIB’s investigation will continue to consider the driver’s actions and factors that may have influenced them, including the industry’s arrangements for advising drivers about poor adhesion conditions and the guidance and instructions relating to reporting low adhesion and driving in such conditions.
Signalling
38 Evidence indicates that the signalling system was operating as designed before the accident. Signal SY31 was at danger as train 1L53 approached it, and the routing of trains across Salisbury Tunnel Junction on the day of the accident was in accordance with normal signalling practice.
Management of low adhesion
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43 On the day of the accident (a Sunday), the RHTT that was due to treat Salisbury Tunnel Junction on the down main line at 17:03 hrs had not yet passed through the area because it had been rescheduled. This rescheduling meant that it would (but for the accident) have passed the junction at around 23:00 hrs. The revised schedule, which was a consequence of planned engineering work between Southampton and Brockenhurst, meant that there would have been an interval of 36 hours between the RHTT runs over the weekend.
44 The last RHTT to run over the junction passed over it at 11:06 hrs on 30 October, around 32 hours before the accident occurred. This RHTT delivered highpressure water jetting, and although it could apply adhesion modifier gel, it was not required to do so on this section of track.
