Axle bearings on Ottawa LRT might need to be redesigned

The way the wheels of Ottawa light rail vehicles meet the rails might not be the main cause of axle problems, according to the city's director of engineering services.

Instead, Richard Holder said there are hypotheses that restraining rails meant to minimize derailments at curves could be putting force on the axles, or transitions on the rail might not be smooth in some locations. 

"We will continue to work with our maintainer on the root cause analysis of the bearing issue," he told the city's LRT subcommittee on Friday. "This may lead to a redesign of the axle bearing assembly in order to resolve this issue long term."

That would be a huge job across the fleet, but it's too early to say if it that will be the required fix, staff said.

Since August 2021, the City of Ottawa, its contractor Rideau Transit Maintenance (RTM), and RTM's subcontractor Alstom, have been trying to figure out why an axle broke and a wheel fell off a train leading to a derailment. The following summer, more light rail trains were pulled from service because of unusual vibrations and maintainers found a damaged wheel hub.

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With no permanent solution yet sorted out, Ottawa's LRT has been running at slower speeds along certain sections of track and has been undergoing extra inspections as a precaution. 

"The biggest issue we face is trying to ensure [the problem] is solved in a sustainable way moving forward," remarked Kitchissippi Coun. Jeff Leiper. 

Alstom report in May

The update on the axle bearings came toward the end of a lengthy presentation about how the City of Ottawa is acting on the 103 recommendations of a public inquiry into the procurement and problems of Ottawa's LRT.

In his report last November, commissioner William Hourigan called that interface between the wheels and rails "the most significant area that must be improved."

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During inquiry hearings in June 2022, representatives from Alstom had presented the theory the stress on the axle components came from excessive pressure going around sharp curves on the Confederation Line.

Nearly a year later, Alstom is due to deliver another report in May to the City of Ottawa. The CEO of Rideau Transit Group, Nicolas Truchon, said it will include a number of hypotheses and lead to a "punch list" of actions to improve the LRT.

Studying the axle issue

Several more investigations have taken place in the year since the public inquiry hearings — Holder showed a flowchart of all the studies and preventative measures.

The National Research Council looked specifically at the interface between the rail and wheel, and recommended reducing friction on curves by adapting the profile of the wheel and grinding the rail, Holder explained. 

Another study focused on the track infrastructure, while the Transportation Safety Board had also done an investigation. 

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Meanwhile, Alstom has put instruments on bogeys to test friction on the rails and forces on axles, at different speeds. Small sensors are also installed on 40 axles on four light rail vehicles as a pilot project to detect vibrations.

Each time a study produces information, there's a deeper understanding of why the wheel hubs might have failed, Holder said.

"At this time, our maintainer believes that the wheel rail interface is not a major contributing factor as part of the bearing issue," Holder told the committee.