Back in September 2024, an aggregates train derailed in Manchester. The UK’s independent watchdog, the Rail Accident Investigation Branch (RAIB), has released its report into the crash. Sheared bolts were the primary cause, but the Branch has been critical of procedural shortcomings.
RAIB has slammed Network Rail over design assurance, installation, inspection and maintenance at a bridge location, which led to a serious derailment. Investigators have also found that the track team in the maintenance unit responsible had neither recorded nor reported similar problems over a period of years. A total of eight safety recommendations have been made.
Previous failures, missing records
In the morning of 6 September 2024, at about 11:25, a bulk aggregates freight train derailed as it crossed a bridge that carries the railway over a public footpath (formerly a local road) in Audenshaw, in the south of Greater Manchester, England. The derailment involved nine of the train’s 24 fully laden wagons and led to extensive damage to the track, the bridge and the rolling stock. No one was injured during the accident, but the railway at this location was closed for around eight weeks, as RailFreight.com reported at the time.
The rails moved under the train, spreading the gauge and derailing the wagons. “The spread was caused by the failure of a number of the screws securing the baseplates to the longitudinal wooden bearers,” says the RAIB report. “Metallurgical examinations showed that these screws had sustained fatigue damage before the arrival of the train. RAIB examinations found that there had been previous screw failures at the same locations. Records of inspection and maintenance activities confirmed that there had been at least three previous failures, although many of the required records were not available.”
Automated and manual inspection didn’t detect trouble
The tracks over the bridge were installed on a typical longitudinal bearer system (LBS), an arrangement in which the rails are mounted on timber bearers that run longitudinally under the rails and not on sleepers and ballast. Critically, the rails are mounted using baseplates, which are screwed onto the bearers. The screw components failed, and this has drawn the ire of the RAIB.
Vehicle dynamics analysis and fatigue calculations (conducted by RAIB) indicated that these screws were not expected to have an infinite fatigue life when installed in the configuration used on the bridge. “The LBS was installed in 2007, and an increase in the volume of traffic over the bridge since 2015 had accelerated the rate of fatigue of the screws,” said the RAIB. “The investigation also found that those screws which had failed had not been detected by Network Rail’s inspection regime. This was because both the automated and manual inspection regimes were not capable of reliably detecting this type of failure.”
Wide ranging recommendations
While the RAIB found that the regular dynamic track geometry measurements were within the allowable limits, it further found that the significance of previous screw failures had not been appreciated. “There were two underlying factors,” Network Rail did not have effective processes for managing LBS assets,” it says in its report. RAIB also found that the track team in the maintenance unit responsible for the LBS at this bridge had neither recorded nor reported previous screw failures, and this had not been identified nor corrected by Network Rail’s assurance regime over a period of years.
As always, the RAIB has stressed that the sole purpose of investigations is to prevent future accidents. It does not establish blame, liability or carry out prosecutions. However, it has made eight stern recommendations to Network Rail. These aim to give greater assurance of the components used in its designs of LBS, improve the management of LBSs, including design, installation and maintenance guidance, and the reporting of component failures. The third recommendation deals with the competence of staff who manage those assets.
Root and branch record keeping
Network Rail should also improve the interfaces between the two disciplines responsible for the track and structures assets, says the Rail Accident Investigation Branch. It also wants Network Rail to better understand the effects of the condition of the LBS supporting structure on the track’s behaviour. It also wants a review of the way changes in rail traffic affect its LBS assets. Traffic over the bridge at Audenshaw had increased significantly since the installation in 2007.
Record keeping, in view of the missing documents, came in for attention from the Branch. The seventh recommendation is to improve the records of its LBS assets, ensuring that it knows the configurations of its LBS assets throughout Great Britain. The eighth recommendation is for Network Rail to improve its own assurance processes for LBS assets to ensure that staff are keeping accurate records of inspection and maintenance activities. It stops short of saying Audenshaw was an accident waiting to happen, but reading between the lines seems as obvious as reading between the widened tracks that lead to this derailment.