Track maintenance vehicle derailment

The challenge

Our client operates rail services across a large metropolitan area, and are also responsible for the maintenance of assets including tracks, trains, signals, stations and facilities. In 2016, a track maintenance vehicle derailed on a section of the rail network, causing considerable delays to both passenger and freight services. An initial investigation of the incident found that both the track and vehicle were compliant to applicable standards. The most likely cause of the incident was the combination of vehicle design parameters and allowable track defect conditions.

As this type of derailment involving multiple factors was new to the client and presented a new and unquantified risk, speed restrictions were imposed on all similar track maintenance vehicles. This subsequently caused further delays to both network traffic and maintenance activities. Understanding this was a short-term solution only, the client sought to engage a suitably qualified consultant to investigate the cause of the derailment, so the imposed speed restrictions could be lifted.

Specifically, the consultant would need to:

• Undertake dynamic modelling of the derailed vehicle to determine the cause of derailment
• Determine the overall performance of the fleet of the single-axle track maintenance vehicles to a range of track and operational conditions
• Advise on how to mitigate potential derailment risks for this type of vehicle.

Our solution

Advisian won the assignment and developed a model of the derailed vehicle (below), validating it against real-world physical tests. A detailed simulation was then undertaken, using measured track conditions of the derailment site. The cause of the derailment was determined to be unstable body dynamic roll behaviour through excitation of the vehicle’s body roll mode, as well as a lack of vehicle damping.

A sensitivity study was then undertaken, using bespoke coding developed by the Advisian team to automate simulation and post-processing. Ultimately, more than 200,000 simulations were run, assessing the fleet of maintenance vehicles against different operational track and vehicle conditions. The results provided guidance on what vehicle and track characteristics, and which vehicle types, should be given more attention to prevent future derailments.

Value delivered

As a result of this work, Advisian was then engaged by the vehicle manufacturer to design additional vehicle dampers to address the dynamic roll instability. Our design was then installed on the vehicle with further physical testing showing stable behaviour. With the root cause of the derailment identified and actions taken to improve vehicle stability, the speed restrictions on the metropolitan line were able to be lifted.