A freight train derailment at Petteril Bridge in Cumbria caused massive infrastructure damage and closed two lines for seven weeks—all because of rail’s equivalent of a car tyre puncture.
In rail, ‘wheel flats’ are faults in the wheels of rolling stock where the curve has been worn away by friction. They have been linked to several other recent high-profile incidents and are a persistent issue for the freight sector.
Flats are costly to repair or replace, can create significant safety risks, and, as seen at Petteril Bridge, they can cause significant damage.
All of which underscores the urgent need for a deeper understanding of this phenomenon.
The physical sequence of events leading to a wheel flat is straightforward: once a wheel stops rotating it slides along the rail surface; friction from the slide wears a flat spot on the wheel; when the wheel is no longer fully round, it behaves unpredictably.
A more complicated issue is why the wheel would suddenly stop rotating.
We know that some wheel flats are simply caused by mechanical failures. A seized axle can lock a wheel in place. A handbrake could be left on by accident. Brake blocks could be incorrectly applied.
However, recent Rail Accident Investigation Branch inquiries are highlighting two emerging issues: Low adhesion on the line appears to be causing more wheel slips. The complex forces at play between moving freight wagons and how the brakes are applied down the train are also a likely factor.
Sourcing solutions
A comprehensive research programme is already under way. With oversight from the Freight Braking and Adhesion Research Group, we are looking into three key areas.
Knowledge frontiers
The first piece of research aims to understand the root causes leading to freight wagon wheel flats. Then, it will develop and share practical ways to reduce that risk. For more information, search T1350 in our catalogue.
The second major study looks at low-adhesion environments. Better knowledge of how freight trains perform in these conditions will bring big benefits. This research will help operators introduce more informed and targeted safety measures. For more information, search T1351 in our catalogue.
The third area of research will look at the complex forces between wagons in a train during braking. This aims to find safe operational limits to minimise derailment risk. For more information, search T1352 in our catalogue.
All the links are also under ‘Related resources’ on this page.
Safety comes first
Our work is driven by safety. With this research, we can reduce the likelihood of these accidents happening again and can promote freight growth by improving reliability and reducing costs.