Taking rolling stock features into account when defining the interoperability thresholds for track and rolling stock

The structure of the Dr18 locomotive causes high lateral forces in turns, which increases wear on the wheel and rail and results in a growing risk of derailment, especially around the heel of the switch.
Due to the cross-approval procedure for the locomotive, the authority responsible for the safety of the railway system did not identify the risks associated with the high lateral forces caused by the rolling stock when granting the authorisation for placing in service for the locomotive series. However, lateral forces and the risk of derailment they cause, especially in switches, came to the attention of the authorities through lateral force measurements later commissioned by the infrastructure manager. The measurements did not result in any measures, even though the safety authority has the preconditions for requiring the railway operator using the rolling stock and the infrastructure manager to take measures to manage the identified accident risks.
In the accident in question, the combined effect of the worn heel of the switch, the worn wheel and the high lateral forces resulted in derailment. The current thresholds do not take into account the safety risk arising from the combined effect of the different components. The TSI requires operators to ensure the interoperability of vehicles and tracks in all situations.

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.

Based on the measurements, all six-axle locomotives have a high risk of derailment around the heel of the switch, which should be taken into account especially when determining use thresholds.

The Finnish Transport Infrastructure Agency seeks to promote the implementation of the recommendation in, for example, Traficom’s rolling stock cooperation groups. A joint meeting on the recommendation was held between the Finnish Transport Infrastructure Agency, Fenniarail and North Rail in March 2025. In discussions with rolling stock managers it has been concluded that it is very difficult to establish unambiguous wear limit values for turnouts and crossings, as the matter is strongly linked with wheel wear and profile, as well as the form of the switch blade in the turnout. In May 2025, the Research Centre Terra published a report on how to reduce the risk of derailment in turnouts. It is stated in the report’s conclusions that, based on the examinations, the measuring gauge is a suitable tool for checking whether the turnout wear is such that it is possible for the wheel to hit the tip of the blade. The development and introduction of a measuring gauge will significantly improve overall safety of turnouts. The guidelines have been clarified in accordance with the study, and the use of a measuring gauge is added to the engineering guidelines for turnouts (Rato 14). The guideline will be piloted in summer 2026. Based on the experience gained from trial runs, the necessary clarifications will be made to the guideline, after which the final version will be published approximately in spring 2027. Further research on switch blades with Research Centre Terra has been launched in 2026. It will also ensure the acute limits of the base part of the switch blade and the optimal form of the switch blade. The Finnish Transport Infrastructure Agency’s superstructure training is currently being reformed, and the measuring issue related to switch blades has been added to the training section on measuring.
As far as Fenniarail is concerned, the practices have mostly remained unchanged. Locomotive maintenance is carried out in accordance with standards and guidelines. The maintenance personnel have been instructed on wheel profile inspections. Fenniarail intends to develop a locomotive-specific monitoring model for systematic monitoring and assessment of wheel profile wear. The company also follows how the matter develops and cooperates with other actors as necessary. In Fenniarail’s view, the recommendation has been partly implemented and included in their continuous development activities.
North Rail has reviewed their guidelines for locomotive wheelset turning, but they have not considered it necessary to change the limit values. Locomotive wheels are measured on a monthly basis, and the results are documented. North Rail has also participated in the assessment work on the risk of derailment and cooperated with other operators. North Rail believes that the recommendation has been implemented for their part.