A derailed freight train caused 2.5 miles of track damage due to a combination of timber degradation and an uneven, defective wagon, an investigation has found.
The Rail Accident Investigation Branch (RAIB) revealed the cause in its report into the incident, which caused the Barking to Gospel Oak line to be shut for 27 days while repairs were carried out.
According to the report, published earlier this week, the freight train departed Barking shortly after 5.30am on January 23 this year and was just minutes into its journey to Calvert, Buckinghamshire when two adjacent wagons near the rear of the train became derailed as it crossed a bridge between Woodgrange Park and Wanstead Park stations.
The wheel of the second wagon rerailed itself after around 230 metres but the first wagon remained derailed, with the train travelling for around six minutes until it came to a stop.
According to the report, “the driver was unaware of the derailment until the brake pipe between the two affected wagons separated causing the train brakes to apply automatically”. The train had been travelling at speeds of up to 35mph before it stopped between Leyton Midland Road and Walthamstow Queens Road.
Shortly after 6am, the driver informed the signaller of a problem with the train, and following an inspection, advised the signaller that one wheel was derailed on a wagon. A Network Rail mobile operations manager attended within an hour and discovered that there was considerable damage to rails, sleepers and cabling.
The report found that the train was running slower than the maximum permitted speed on that section of the track, adding: “There is no indication that the handling of the train had any influence on the cause of the derailment.”
It also considered external factors, such as the time of day and the weather, but found that the conditions were “unlikely to have had any bearing on the accident”.
Although nobody was injured in the incident, the derailment required a significant amount of repair work to be carried out on the track.
This included replacing 39 pieces of rail, 5,300 concrete sleepers and 900 wooden sleepers, as well as removing and replacing 10,000 tonnes of ballast and replacing timbers supporting the track at 10 bridges. Lineside cables and signalling equipment were also repaired.
Investigators carried out an analysis of the track and found that the “derailment was a consequence of rail movement causing the track gauge (the horizontal distance between the rails) to increase by at least 85 mm, sufficient to allow the right-hand wheel of a wagon to drop inside the right-hand rail”.
They found that timber degradation was an issue on the bridge, but determined that “Network Rail was not aware of the severity of the longitudinal timber degradation and so took no action to deal with this”.
Ellie Burrows, route director for Network Rail Anglia, said: “We accept we relied too heavily on the GPS data for our track inspections, which wasn’t accurate enough, and as such we missed the opportunities to adjust the gauge of the track before the derailment at Wanstead Park.
“We’re grateful that no one was hurt and very sorry that the resulting damage caused weeks of disruption to passengers and our freight customers. Since the incident, we have reviewed and improved our maintenance inspection and reporting processes to prevent any future incident.
“In addition, all softwood longitudinal timbers that were damaged during the derailment have been replaced with hardwood.
“We now use a new testing technique that enables us to inspect the inside of timbers and identify if it is rotting. In addition, all of our wheel timber inspectors have undergone specialist training to help them identify hidden problems and we have appointed a senior asset engineer to coordinate our wheel timber programme.”
The RAIB investigation explained that the train and wagons involved in the derailment were used on a daily round trip between Barking and Calvert, and on the day in question was carrying 1,435 tonnes of clay spoil.
It would return empty each time to be reloaded overnight, and the first wagon to derail - referred to as 3415 - had been loaded up as part of the same train nine times in 2020, including on the two previous days.
Investigators found that it had been loaded in such a way that it “did not exceed the maximum gross vehicle weight, but the load was concentrated towards the rear right corner of the wagon”.
The wagons are owned by VTG Rail, with the company also responsible for their maintenance.
The report added: “The need for frequent replacement of some wheelsets on wagon 3415 [...] provided VTG with an opportunity to recognise a problem requiring consideration as a possible safety issue. However, the problem was not identified.
“VTG provided records of wear patterns for wheelsets fitted to other wagons in the same train, and RAIB found no other examples of wheel wear occurring as rapidly as on wagon 3415.”
The report recommended that “VTG should review and improve monitoring of maintenance activities on individual rail wagons to detect repetitive maintenance requirements which may indicate an underlying fault”.
VTG did not respond to a request for comment.
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