The driver heard a loud bang and saw sparks as a rush hour train derailed between Sheffield and Doncaster, causing huge disruption.
The train had just left a depot in Doncaster on December 21 and was negotiating a tight curve when the third of four carriages came off the tracks at around 5.15pm.
No one was injured but the recovery operation and damage to the tracks left the line between Sheffield and Doncaster blocked for 36 hours.
A report by the Rail Accident Investigation Branch (RAIB), published today, states: “The driver of the train reported feeling a jolt and hearing a loud bang.
“He looked out of his window, saw sparks from the class 37’s front bogie (undercarriage) and immediately applied the brakes.”
The investigator found no evidence the driver was at fault but said the curve should have been fitted with check rails to reduce the risk of derailment.
The train in question had recently had its wheels turned to repair wear and tear, the investigation revealed, increasinmg the friction between the wheel and the rail, and making a derailment more likely.
The watchdog's report also criticises the delay in launching a thorough probe.
“Following the derailment, detailed inspection and measurements of the track were undertaken by Network Rail,” it states.
“However, no higher level industry investigation was commenced until almost two months later, by which time it is possible that other vulnerable or perishable evidence may have been compromised.”
The report says the accident highlights the increased risk of derailment for trains with newly turned wheels operating on tight curves without a check rail and adequate lubrication.
It also calls for the rail industry’s own investigation of derailment to be pursued in a ‘timely manner’ to ‘preserve evidence and learn lessons to prevent or minimise recurrence’.