R2023-02 Derailment of a freight train in Tampere on 30 November 2023

On 30 November 2023, the locomotive of freight train T7121 and the front bogie of its first wagon became derailed at the switch V171 to the north of Tampere station. No personal or environmental damage was caused by the accident. As a result of the derailment, the switch V171 was severely damaged and only one track between Tampere and Lielahti remained in use until 3 December 2023. The derailment and prolonged track clearance caused significant traffic disruptions, and some trains had to be cancelled.

The accident was caused by the combined effect of various factors, which included the worn heel of the switch, the high lateral force on the rails characteristic of the locomotive type, and the worn wheelset of the locomotive.

At the time of the incident, the switch V171 had worn down to its critical operational and maintenance threshold. The switch also had an abnormal wear profile, which contributed to the rising of the wheel of the locomotive and its staying on the tongue of the switch. The track maintenance operator had noticed that the switch was worn out but did not present a repair plan to the client, while the client also did not require the plan.

The monitoring of the condition and wear of the switch currently partly relies on sight-based inspection, and measuring instruments such as gauges are not used systematically. In addition, the instructions prepared to support maintenance have inconsistencies and are not easily accessible.

As the plan was to replace the switch V171 in connection with a railway yard renovation project, there was an aim to minimise the maintenance of the switch before the start of the renovation project. However, in deviation from the plan, the renovation project was delayed several times at the annual level, and the impacts of the delay on the switch maintenance plan were not reassessed.

The Dr18 locomotive was brought to Finland through a cross-approval procedure. For this reason, the approval process was more limited in Finland and the authority responsible for the safety of the railway system was unable to identify the high lateral forces caused by the rolling stock to the track when granting the rolling stock authorisation for placing in service. The infrastructure manager commissioned lateral force measurements on various equipment, which showed that the structure of the Dr18 locomotive causes high lateral forces on the track. High lateral forces increase the wear of the track and wheels, leading to a higher risk of derailment of rolling stock, especially around the heel of the switch. The revealed risk of derailment led to no action.

In addition to the lateral forces and the worn heel of the switch, the risk of derailment was also increased as the wheels of the derailed locomotive were worn nearly to the point of being unfit for use, which weakened the directional capacity of the wheelsets at the switch. In addition, a curve had formed on the wheel flange, which had a significant impact on the derailment. With regard to the wheels of locomotives, the effect of the flange tip and the shape of its wear on the operational performance of rolling stock has not been identified and it has not been addressed in the rolling stock maintenance instructions.

The investigation revealed that the current safety risk monitoring and management practices have mainly focused on assessing critical thresholds for individual factors. They do not take sufficient account of the cumulative safety risk arising from the combined effect when several elements are close to the critical threshold, as was the case in this accident.

In addition, the investigation showed that cooperation between different operators was one of the key factors in the success of clearing. When examining clearing operations, it was found that rolling stock maintenance operators have equipment and resources suitable for clearing operations that are currently not utilised efficiently in clearing operations on the state-owned railway network. More extensive cooperation could minimise the duration of disruptions in the rail network and their impact on the functioning of society.

To improve safety, the Safety Investigation Authority recommends that:

1. The Finnish Transport Infrastructure Agency ensure the uniformity of the guidelines and improve their accessibility, unambiguously define the method of measuring the maintenance needs of the heel of the switch, and specify accurate wear profiles for the heels of the switch. [2024-S33]
2. The Finnish Transport Infrastructure Agency examine the track maintenance process so that the impacts of delays in renovation projects on maintenance are taken into account in more detail when planning maintenance. [2024-S34]
3. Railway operators and rolling stock maintenance operators draw up instructions for inspecting the shape of the wheel flange and include a guided inspection as part of the maintenance of wheelsets. In addition, a procedure must be introduced for monitoring the wear of rolling stock wheelsets to identify and anticipate wear on the wheels between maintenance. [2024-S35]
4. Infrastructure managers, railway and clearing operators and rolling stock maintenance operators agree on cooperation practices in relation to clearing to ensure smooth clearing operations. In addition, the stakeholders proactively examine the tools and resources available and agree on their use and related communication in clearing situations. [2024-S36]
5. Infrastructure managers and railway operators using six-axle locomotives jointly define safety margins for the wear of the track and the wheelsets of rolling stock that ensure safe operation, taking into account the combined effect of different factors. [2024-S37]