The axle hub assembly issues in Ottawa’s light-rail transit vehicles have been traced back to higher than anticipated lateral loads exerted on the vehicles’ axles when they are in operation. The issue was identified by Alstom, although no unity of thought currently exists between Rideau Transit Maintenance and Alstom regarding the root of the axle issues. However, both companies concur on a number of steps necessary to forge a “sustainable solution”. This solution is aimed at reducing the loads at the wheel-rail interface, and encompasses a top-of-rail lubrication scheme for the rail line.
A report regarding the root cause of the axle bearing issues on the O-Train vehicles has been delivered by representatives from OC Transpo, Rideau Transit Maintenance and Alstom. The report details the issues that have arisen with the wheel hub and axle-bearing since 2021, which include three major incidents and a derailment at Tunney’s Pasture station. The O-Train service underwent a 28-day interruption in the heart of summer due to an axle hub assembly found to be excessively greased during a routine inspection.
Alstom’s engineers have determined that the preload-providing restraining nut within the axle cartridge has the potential to “unlock”. In response, a proposal has been submitted to the city by Alstom to modify the nut by inserting restraining pins intended to prevent this unlocking.
In their root cause investigation, Alstom found the lateral loads on the wheel hub assembly to be “higher than expected” – a conclusion they purport will guide them in their formulation of both short-term and long-term solutions to the axle problem.
The wheel assemblies of the vehicles, it was stated to the Transit Commission, are experiencing lateral loads which go beyond the design parameters during operation. This leads to the axle hub assembly being subjected to bending loads, and ensuing malfunctions like the unscrewing of the restraining nut – even a derailment.
David Van der Wee, Alstom’s vice-president, pointed out to the Transit Commission that “this failure mode we see here in Ottawa, we have not observed in our other fleets around the world”. His comment draws attention to the uniqueness of the issue faced by Ottawa’s light-rail transit vehicles.
Despite their collective effort to identify the root cause of the axle hub assembly problems, consensus is yet to be achieved between Rideau Transit Maintenance and Van der Wee. Regardless of the conflicting views, both parties agree that the nut coming unscrewed is a significant part of the problem. Van der Wee stressed the importance of this aspect, stating it should remain the central focus of investigation even as they work out the sequence of events leading to the unscrewing of the nut.
Solutions for the lateral load issues as proposed by Alstom include top-of-rail lubrication, coefficient of friction management, improving infrastructure and increase design limits. Several recommendations have been further submitted to Rideau Transit Maintenance to create a sustainable solution. These involve moving the restraining rail, deploying top-of-rail friction modifier, improvements to ballast shoulders, and replacing the current soft rail with a harder variant.
It is interesting to note, Rideau Transit Maintenance shared with the Transit Commission that the top-of-rail lubrication is a water-based and environmentally friendly product. The use of this product along the O-Train line has demonstrated a loss of 40% in lateral loads.
These proposed improvements – some already tested others yet to be implemented, are all vital components being brought to bear on this issue. Implementation of the proposed locking nut for the axle is under consideration, a move that could significantly reduce the current inspection regime, thus offering the potential to increase the fleet size and improve service. Also, the utilisation of a harder rail is being examined, which could likely require substantial rail alterations and necessitate a potentially lengthy overhaul of the existing tracks.
However, whether these measures will be universally agreed upon or near enough to be implemented remains to be seen. As Nicholas Tauchon, RTG president, expressed, “We may get to an agreement with Alstom on their theory, but we’re not quite ready to go there yet.”