“The company that was contracted to construct the drain, Carillion, did not undertake construction in accordance with the designer’s requirements,” says the report by the Rail Accident Investigation Branch. “Consequently, the drainage system was unable to perform as the designer had intended when it was exposed to particularly heavy rainfall.”
At around 09:37 hrs on Wednesday 12th August 2020, a passenger train derailed near Carmont, Aberdeenshire. The train was travelling at 73mph, just under the normal speed for the line concerned. After derailing, the train deviated to the left, before striking a bridge parapet which caused the vehicles to scatter. Three people died as a result of the accident and the remaining six people on the train were injured.
On the morning of the accident there was near-continuous heavy rain at the site of the accident between about 06:00 hrs and 09:00 hrs. The 51.5mm of rain that fell in this period at the accident site was close to the average rainfall for the month of August in this part of Scotland. Train 1T08 derailed because it struck debris that had been washed out of a drainage trench. This trench, which had been constructed between 2011 and 2012, 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. However, 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.
RAIB’s investigators found that a low earth bank (bund) had been constructed that ran across a slope leading towards the track. The presence of this bund significantly altered the flow of water such that extreme rainfall would cause a concentrated flow into the steeply sloping section of trench. The evidence indicates that the intensity and duration of this rainfall would have generated water flows into the trench that were sufficient to wash away the gravel fill and the ground immediately surrounding the trench.
“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,” says the report. “This bund, which was constructed outside Network Rail’s land, had the eﬀect of diverting a large amount of water into a gully so that it all reached the drain at the same location, thereby increasing the propensity for washout of the gravel infill. RAIB found no evidence that the construction of the bund was notified to Network Rail or the designer.”
No instruction was given by route control or the signaller that train 1T08 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. Consequently, normal railway rules were applied to the train movement. The RAIB’s investigation found that the ‘route controllers’ (who were 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.
As a consequence of this accident, RAIB has made 20 recommendations for the improvement of railway safety, including better management of civil engineering construction activities by Network Rail and its contractors.
Simon French, chief inspector of rail accidents, said: “This was a tragedy that devastated the lives of the three families who lost their loved ones and brought terror and injury to six other people on the morning of 12 August 2020. Our thoughts are with them all. Nothing can undo this event, but we owe it to everybody who was affected by it to strive to learn safety lessons for the future.
Network Rail chief executive Andrew Haines 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 of pounds 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.”