A Rail Accident Investigation Branch (RAIB) investigation has found that errors in the construction of a drainage system were the primary cause of a fatal train derailment at Carmont in Aberdeenshire last year.

Three people died as a result of the accident and the remaining six people on the train were injured.

Commenting on the RAIB report on the crash, Simon French, Chief Inspector of Rail Accidents, said:

“Although railway safety in the UK has been steadily improving over recent decades, the tragedy at Carmont is a reminder of just how disruptive and potentially dangerous Britain’s volatile weather can be.

“The railway industry needs to get even smarter about the way it counters this threat, and to better exploit remarkable modern technology that enables the prediction and tracking of extreme weather events such as summer convective storms.

“There’s also an urgent need for the railway to provide real-time decision-makers with the information, procedures and training they need to manage complex and widespread weather-related events across the rail network.”

He went on to say that the investigation had highlighted the risk of uncontrolled changes to railway infrastructure during construction. A project that was designed for the protection of the travelling public became unsuitable for its intended use and posed a hazard to trains because of such uncontrolled changes to the design.

He continued:

“The original designer needs to understand the change that’s proposed and review the implications of a change that may appear inconsequential to the team on site. I hope this example will resonate throughout the UK’s construction industry.

“It’s important for all of us in the rail industry not to dismiss this truly harrowing accident as a one-off event. The railway industry needs to think through the implications of severe weather on its infrastructure, whilst also looking to the behaviour of trains should they derail after striking obstructions such as washouts and landslips.”

Catalogue of errors and failures in construction and Network Rail processes

The derailment happened at around 9:37 am on Wednesday 12 August 2020 – the service from Aberdeen to Glasgow, was returning towards Aberdeen due to a blockage that had been reported on the line ahead. The train was travelling at 73 mph (117 km/h), just under the normal speed for the line concerned.

The RAIB investigators found a catalogue of errors and failures in both the construction of the drainage system and Network Rail’s processes to ensure the work had been carried out correctly. The report draws attention to an ongoing series of failures in maintenance since construction of the system was completed in March 2013.

The report says that Carillion, the company that was contracted to construct the drain, did not undertake construction in accordance with the designer’s requirements. The trench was designed by Arup and constructed between 2011 and 2012.

Consequently, the drainage system was unable to perform as the designer had intended when it was exposed to particularly heavy rainfall on 12 August 2020.

Train 1T08 derailed because it struck debris washed out from a 15 metre length of a steeply sloping drainage trench constructed by Carillion. The contractor collapsed in January 2018 in the UK’s biggest corporate failure in decades - it failed with debts of £7 billion, more than its annual sales of £5.2 billion

The trench contained a perforated pipe that had been installed as part of a project to address a known problem with drainage and the stability of a cutting in that area.

Design of drainage system would have been capable of safely accommodating flow of surface water

Modelling undertaken as part of the investigation by engineering consultancy firm AECOM (appointed by RAIB) indicated that Arup’s design of the 2011/12 drainage system at Carmont would have been capable of safely accommodating the flow of surface water that occurred on the morning of 12 August 2020 without causing gravel to be washed away down the steeply sloping trench towards the track.

However, the investigators found that the drainage system and associated earthworks had not been constructed in accordance with the original design and so were not able to safely accommodate the water flows that morning.

Failures in processes to capture data needed for inspection and maintenance activities

In addition, information about the section of the drainage system nearest the track at Carmont was held in Network Rail’s infrastructure maintenance database (Ellipse). However, when construction was completed, the remainder of the Carmont drainage system should have been, but was not, entered into Ellipse to trigger routine inspection and maintenance activities.

The report says this did not happen due to non- implementation of Network Rail’s procedures for introducing new assets onto infrastructure. RAIB found no evidence that Network Rail undertook any inspection of the upper parts of the drainage system in the period between the inspection of the completed works in March 2013 and the accident in August 2020.    

The most significant difference between the original design of the drainage system and the final installation was the construction of a bund running across the slope towards the railway and perpendicular to the 2011/12 drain. RAIB found no evidence that the construction of the bund was notified to Network Rail or to Arup.

The contractual arrangements between Network Rail and Carillion meant that Carillion was responsible for the delivery of works in accordance with designs approved by Network Rail, together with amendments agreed through formal processes during the construction phase of the scheme.

There is no evidence that changes such as the construction of the bund and omission of the connections from the existing drainage to a catchpit were dealt with as part of a formal process, the report concludes. Changes of this type should have been referred to Arup.

Network Rail’s audit regime at the time of the drain’s construction did not include audits likely to detect design modifications implemented on site without proper change control.

Although Network Rail had a project team, they were not required by Network Rail business processes to check that the drain was being installed in accordance with the design. The report says the project team were “probably unaware” that the 2011/12 drain was significantly different from that intended by Arup and therefore did not take action, instead relying on a contractual assurance process that required Carillion to refer proposed changes to Arup for approval.

The investigation also refers to the requirement for the preparation and retention of ‘as-built’ drawings of newly constructed assets to assist future maintenance of the asset, which can provide an opportunity for the designer to recognise inappropriate design modifications. However, RAIB found no evidence of any such drawings being submitted to Arup or Network Rail.

Deficiencies in operational guidance in event of extreme weather events

The investigation also found deficiencies in operational guidance at the time of the derailment - no instruction was given by route control or the signaller that the train should be run at a lower speed on its journey between Carmont and Stonehaven. At that time there was no written process that required any such precaution in these circumstances - normal railway rules were therefore applied to the train movement.

The RAIB’s investigation found that the route controllers responsible for the operational management of Scotland’s railway network had not been given the information, procedures or training that they needed “to effectively manage complex situations of the type encountered on the morning of 12 August 2020.”

Recommendations

As a consequence of the accident, RAIB has made 20 recommendations for the improvement of railway safety. The areas covered include:

• better management of civil engineering construction activities by Network Rail and its contractors
• additional standards and guidance on the safe design of drainage systems
• improved operational response to extreme rainfall events, exploiting the full capability of modern technology, and based on a detailed understanding of the risk associated with extreme rainfall
• enhancing the capability of route control offices to effectively manage complex events
• extending Network Rail’s assurance regime to encompass route control offices
• addressing the obstacles to effective implementation of lessons learnt from the investigation of accidents and incidents.

Commenting on the publication of the Rail Accident Investigation Branch (RAIB) Carmont report, Andrew Haines, Network Rail chief executive, said:

"This report makes clear that there are fundamental lessons to be learnt by Network Rail and the wider industry. As well as expressing our deep sorrow and regret at the loss of the lives of Christopher Stuchbury, Donald Dinnie and Brett McCullough, it’s important that we acknowledge it should not have taken this tragic accident to highlight those lessons. We must do better and we are utterly committed to that.

“In the 18 months since the accident, we have inspected similar locations and drainage systems across the length and breadth of the country and the added insight the RAIB has provided today will help us in our efforts. We also commissioned two independent taskforces led by world class experts to help us better understand extreme rainfall events and how to better manage our cuttings, embankments and their drainage systems.

"We have invested tens of £millions towards improving the general resilience of our railway and how we predict and respond to such events. But this remains a multi-generational challenge and there is still much to do.”

Click here to download the RAIB report in full