The importance of measuring the distribution of vertical forces per wheel in static conditions for maintenance
The correlation between derailment of a rolling stock and an uneven distribution of vertical wheel forces is addressed in multiple post-derailment investigations carried out in different areas. Japan, Australia, India, America and the United Kingdom are just some of the many countries that have identified load wheel imbalance as the main cause, or contributing factor, of accidents during post-derailment investigations. Some of the investigations are available at the following links:
Japan:
Railway accident investigation report in Mojiko station
Australia:
India:
The Investigation of Derailments
United States:
Safety Advisory 2013-02: Low-Speed, Wheel-Climb Derailments
United Kingdom:
RAIB report 07/2020: Freight train derailment at Willesden High Level Junction
For example, the latest investigation above mentioned took place in the UK. The accident involved a freight wagon which was running on a junction expected on the route. However, one of its empty two-axle wagons derailed.
The RAIB (Rail Accident Investigation Branch) investigation revealed the combination of the following two factors as the cause of derailment:
- A considerable twisted track
- Load on the left front wheel not enough to prevent a derailment
Later, the second factor has been verified: it was the direct consequence of a significant load imbalance between the wheels on the two diagonals of the axle wagon. As a result, the set-up of the wagon did not allow the vehicle to adapt to such a strong and abrupt twisted track while running.
To learn more about how the homogeneous load distribution makes a general railway vehicle capable of adapting to a twisted track, see the topic “Wheel load distribution”.