The Rail Accident Investigation Branch (RAIB) has called for Network Rail to use weather forecasting processes to better understand the implications of snowmelt on slope stability after a train was derailed in Scotland earlier this year.
According to RAIB, the combination of rapid snowmelt and rainfall caused the landslip on 22 January 2018 near Glenfinnan which was struck by a passenger train travelling between Mallaig and Fort William.
RAIB found that Network Rail’s processes for managing landslip risk did not take account of the hazard caused by rapidly melting snow, but said it was unlikely that a greater understanding of snowmelt risk could have avoided or mitigated an accident in other circumstances.
The leading coach of the two-car train derailed to the left and came to a halt embedded in the landslip debris. The line was closed for a week after the incident.
It is estimated that between 500m³ to 600m³ of material slipped on the track (around 1,000t) and the top of the landslip started at a natural hollow about 80m outside the railway boundary fence, and 46m above track level. The slip followed the path of an existing gulley, enlarging it significantly down to the level of the underlying bedrock according to the report.
According to the RAIB report, the landslip originated from a natural hillside above the railway and was triggered by a combination of rainfall and snow melting during a rapid thaw. The report suggests that the ground may have been saturated before it froze.
A protective fence, which had previously been installed near the railway to trap falling rocks was ”overwhelmed by the event”.
RAIB’s report into the incident recommended for Network Rail to promote the development of weather forecasting processes to take account of risk due to snowmelt and ground thaw.