The Accident Investigation Board has found that the collision at Helsinki Railway Station in early January was caused primarily by the detachment of a coupling hook between rail carriages.
The decoupling was caused largely by ice and packed snow that had accumulated between the coaches. The ice and snow also prevented the conductor from noticing that the hook was not connected right.
On January 4th, four coaches of an InterCity train which was scheduled to leave for Kajaani became detached from the rest of the train, which was being shunted to the station.
The runaway cars overran the buffers and crashed into an office building at the end of the track.
Guards at the station managed to clear the nearby platforms and trains of people, preventing serious injury.
No brake malfunction was detected on the train; the conductor had released the brakes to get the stopped carriages on the move.
According to Esko Värttiö, the head of the investigation, the carriages would not have got away if the coupling hook had been in place.
He also said that both the conductor and the rest of the personnel acted according to instructions in the chain of events that led up to the accident. The final report of the board is expected at the end of the year.
The Finnish rail company VR has issued new instructions following the accident.
According to the guidelines, brakes on train carriages being moved between Pasila and Helsinki stations should be released only when there is a separate auxiliary locomotive between the carriages and the station, making sure that the carriages stay in place.