R2012-02 Derailment of turnout transport wagons in the Riihimäki railway yard, Finland on 22 May 2012 and Kouvola railway yard, Finland on 28 June 2012
At 3:09 a.m. on Tuesday 22 May 2012, a turnout transport wagon, positioned as the 16th wagon of a freight train and carrying two turnout elements with concrete sleepers, was derailed at the southern end of the Riihimäki railway yard. When the derailing occurred, the train was running through the yard's turnouts at a speed of 26 kmph. The derailed wagon and its load finally fell onto the adjacent track. The accident inflicted damage to the track and track equipment and significantly hindered railway traffic until the following evening.
About a month later, at 1:20 p.m. on 28 June 2012, a similarly loaded turnout transport wagon was derailed in the Kouvola railway yard. This wagon was the last car in a 20-car train. It was derailed when travelling through the turnout and finally toppled onto the adjacent track. The speed of the train at the moment of derailment was 14 kmph. Some changes were required to the hump yard arrangements, due to the track and track equipment being damaged. The accident did not significantly hinder train traffic.
Imbalanced loading caused the sideways load balance distribution of the turnout transport wagon to be very uneven. The wheel-weight ratio was 1:1.96, meaning that wheels on one side were carrying almost double the load compared to wheels on the other side. This caused the frame of the wagon to lean heavily on the side bearer blocks placed on top of the bogies. Due to the remarkable imbalance, significant friction was generated between the frame and side bearer block. This friction made it difficult for the bogies to turn when travelling on curves and through turnouts. The wagon's bogie pivot centres were also rather dry and somewhat rusty. This required the use of more force for turning the bogie.
In the Riihimäki accident, the head of the rail was cracked at the spot where the derailment occurred. In Kouvola, the turnout at the derailment spot was in poor condition, featuring wear exceeding the allowed measurement values. Moreover, the track featured dents of varying depth around the turnout. These flaws and wear contributed to the wheel flange rising on top of the rails. Similar turnout transports with imbalanced loads have been previously carried out without any problems. This fact supports the notion that wear and flaws in the track played a key role in the accidents.
In order to avoid similar accidents in the future, the Safety Investigation Authority, Finland recommends the following:
- The turnout transport wagon should be modified in such a manner that it can transport turnout elements, while ensuring that the wheel weight ratio complies with general loading instructions (1.25:1 at maximum).
- Drafting of the turnout transport wagon's loading instructions should be completed so as to ensure that these instructions are unambiguous and precise and that compliance with them guarantees that loading is performed in accordance with the wheel weight ratio and rolling stock gauge determined in the general loading instructions.
- The risk assessment element of the safety management system should also extend assessment to existing standardised activities.
- In the turnout condition monitoring system, turnouts that have been found to be in poor condition should be repaired or replaced to ensure that they fulfil the measurement values and other requirements set for turnouts.
- Unambiguous operational instructions regarding maintenance and traffic limitations should exist for cases in which the measurement values and acute limits determined for turnouts are exceeded.