Alstom report blamed soft tracks, design flaws for LRT derailment

The consortium that oversees Ottawa's LRT system and the French subcontractor that built its trains have long disagreed over a simple issue: Why did a train derail four years ago?

They agree that a wheel hub assembly, which joins the axle to the wheel, failed. Bearings wore down too quickly. A nut came undone. In August 2021, that caused the assembly to fall apart.

But they have differed over why this is happening. 

Publicly, their disagreements have been muted, aired only in the form of hints dropped during transit commission meetings.

Alstom said forces from the rails were overloading the assemblies, and it recommended changes to the tracks. RTG resisted that, saying some changes needed further study.

Now, after a year and a half of fighting through the freedom of information process, CBC has obtained a May 2023 report that reveals the true depth of that divide — a report in which Alstom clearly places the blame on the tracks, claiming they fall short of industry standards.

Alstom says the tracks are softer than the wheels. It says restraining rails are incapable of preventing derailments, and might even be worsening rail kinks at critical spots. It says the rails were designed for the wrong temperature, and unexpectedly shift to the side.

RTG has questioned the report, which was long withheld from the media and even city councillors, and urged Alstom to pursue a different solution: a full redesign of the wheel hub assembly.

But the Alstom report casts doubt on that. It says fully redesigning the wheel hub assembly on its trains is neither necessary nor viable.

Patrick Dumond, an engineering professor at the University of Ottawa who specializes in the monitoring and diagnosis of bearing faults, said the conclusions in the report aren't really surprising.

"Alstom obviously has a vested interest in it not being their problem," Dumond said, noting that redesigning the axle hub would cost the company money, while changing the tracks would not.

Still, he called the Alstom report thorough and said the problems it raises appear serious. He said they should be fixed, though doing so would be a costly proposition.

"Ripping up rail is expensive," said Dumond.

OC Transpo and RTG deferred questions about the report to an upcoming technical briefing on the status of current measures and next steps.

Contentious recommendations

Alstom's report, entitled "Ottawa LRT Recommendations for a Sustainable Solution," draws on a long list of earlier studies and the company's own testing. It says the failure that caused the 2021 derailment didn't stem from a manufacturing error, nor from the design of the axle hub assembly itself, but from excessive forces coming from the rails.

The company said its testing found forces exceeded design limits by as much as 41 per cent on one curve.

The report says adding lubricant could help relieve those forces. It also recommends making minute adjustments to improperly placed restraining rails, which run along the inner track at curves to prevent derailment, to stop them from striking the wheels.

RTG agreed to those measures in October 2023, when a summary of the report was presented to city councillors. It resisted other recommendations that were mentioned in passing, though their full rationale was not spelled out.

The report says the rails are much softer than standard industry rails, and even softer than the train wheels, which "is not standard industry practice." That results in greater rail wear, especially at curves, according to the report.

That wear includes corrugation, a wavy pattern along the surface of the rail that can cause vibrations and increase friction, putting added forces on the trains.

As a result, Alstom recommends replacing the soft rail with harder rail at curves, stations and other key areas.

It recommends yet another change to the restraining rails. Shifting them to the side might stop them from contacting the wheels, but it won't fix another problem. According to the report, the rails are also too short.

They start and end within the curve of the rail, rather than extending into the straight portion of the track beyond. That's also contrary to industry practice, according to the report.

"In its current configuration, the restraining rail is not capable of fulfilling its function of preventing a vehicle from derailing," the report says.

Restraining rails also act like a splint, reinforcing the sections of track they run along. Ending them right at the entrance to a curve results in "an abrupt reduction in the stiffness of the track" and can cause kinks at a crucial spot. 

"A rail kink immediately before a curve spiral aggravates the increased stresses imposed on the vehicle by the curve," it says.

Those kinks were in fact observed at five curves, according to the report. Alstom recommends that the restraining rails should be extended beyond the curve into the straight portions.

As of the last update in May 2024, there were no plans to carry out those two recommendations.

Assembly redesign questioned

At that time, RTG said it had its own report casting doubt on Alstom's findings. It told a transit commission meeting that Ottawa's LRT "has no unique features and is currently maintained within the applicable standards."

The report found nothing unusual that could damage the trains. Unlike in October 2023, Alstom did not attend last year's meeting.

RTG CEO Nicholas Truchon said rail lubrication is more important than harder rail in reducing wear and controlling forces on the wheels. He said it's better to wait and see how it works "before jumping to conclusions and stripping down track."

Truchon said RTG will consider harder rail, but only when rail comes up for normal replacement. He said the rail on Ottawa's LRT is allowed under RTG's contract and "is also part of the industry standard." 

If the problem stems from hard wheels and soft track, Truchon said it might also be easier to replace the wheels than to replace the track.

Both RTG and OC Transpo have asked Alstom to design a new wheel hub assembly. Alstom later halted the work, but RTG later directed it to renew it.

But in the 2023 report, Alstom said the current design will work fine if its recommendations for changes to the track infrastructure are completed.

"While Alstom continues to investigate, new axle hub assembly concepts do not appear to be a viable sustainable solution for deployment across the Ottawa fleet," it said. "A full component redesign is a significant engineering undertaking, requiring extensive testing and validation, before production can even begin."

It said a new design might sustain higher loads, but "would likely still be unable to sustain the most critical loads, as recorded during the instrumented axle tests."

Dumond said fixing the tracks or fixing the trains shouldn't be an either/or choice. While it appears the tracks do have issues, there are also questions about the trains.

The City of Ottawa asked Alstom to move 24,000 passengers per hour on a light rail system, Dumond noted. Those are subway-level volumes, pushing the limits of the vehicles and putting added pressure on the bearings.

"I think if you're going to design a new train that's bigger and heavier and you're seeing problems, then I think you probably do want to fix it at the source of the problem, which is the wheel hub assembly," he said. "Make that robust enough to handle all loads that we're seeing in the train."

Who blocked report's release?

A short summary of the report was attached to a transit committee agenda in October 2023. At the time, Dumond said it was so vague that it shed little light on the actual root cause of the derailment. 

Alstom and RTG then appeared at council's transit commission that month to present elements of the report and to answer questions. They focused mainly on top-of-rail lubrication and preventing restraining rails from contacting wheels, largely glossing over the more contentious recommendations.

Councillors did not receive the actual report, though many of the issues it raised had shown up in earlier studies. 

The city told CBC at the time that it was "working with Rideau Transit Group (RTG) and its partners to determine next steps regarding requests for documentation."

CBC requested the original report through a freedom of information request in late 2023. The city soon agreed to provide several dozen key pages, though not the entire 1,000-page report.

But a third party objected even to that, and appealed the decision to Ontario's information and privacy commissioner, saying the documents contain "sensitive technical and commercial information."

The dispute went to mediation and then to an adjudicator, who found in CBC's favour. The third party's name was redacted throughout the process, though its submissions do reveal some clues to its identity.

The party is a contractual partner of Alstom and is involved in ongoing legal disputes with the city.

RTG, a contractual partner of Alstom that is involved in legal disputes with the city, did not respond to CBC's inquiry about its role.

Read the Alstom report pages provided to CBC