Understanding the O-Train wheel problem
Three interviews with engineers shed some light on a complex problem
Two big LRT updates out of City Hall today: Service is expected to restart by Monday, July 31; and Alstom and RTG have agreed to redesign and replace the wheel hub assembly on all light rail vehicles.
We’ve known there have been problems with the wheels for a while, at least since the August 2021 derailment.1 The axles and bearings are supposed to last 1.2-million kilometres, but they’re showing problems far, far earlier than that.2 In the words of Rideau Transit Group (RTG) officials, the new wheel hub assembly will “strengthen” the axle so that it can handle normal operating conditions.
What exactly are wheel bearings and what do they do? Why has it taken so long to figure this out? What can be done to fix this?
On Sunday I biked from Stittsville to Britannia Beach and caught up on some listening from the past week. CBC’s Ottawa Morning aired three excellent interviews that, taken together, paint a really clear picture about the wheel problems plaguing the LRT in Ottawa, and how a solution can be found.
All three are with engineers; and two are from outside of OC Transpo. I encourage you to take 30 minutes or so and listen to all three. Links to each interview are below along with some key quotes.
Dumont is a mechanical engineer and professor at the University of Ottawa and gives an excellent primer on wheel bearings, and what might be causing them to fail.
Q: The General Manager of OC Transpo said “the bearing play was over the threshold at which it could stay in operation”. Can you decode that for us?
A: In the original TSB report, they indicated that the tolerance of play was 0.1mm which is really small when you think about it. When it comes to bearings, this indicates that there’s probably been a failure of some sort, there’s been an excess of wear in the material, which would lead to more problems later if we let it keep running…
Q: When we think about the LRT, it’s still relatively new. How common is it for bearings to wear down or need to be replaced?
A: Typically it’s not very common but it can occur. Bearings are designed to last for a very long time… unless there’s a flaw in it that can cause it to fail prematurely. In this case, from what I’ve read, the whole drive assembly and the trains were designed to last for 1.2-million kilometres… so the fact that it failed so early in the train’s life is very odd.
Holder is the director of engineering services at OC Transpo. He provides details about what components are being tested on the trains and on the tracks, and what they need to understand before putting the trains back in service.
Q: Do you foresee a point where the entire rail line will have to be ripped up and replaced or new trains ordered?
A: No, I don’t see us getting to that place. I think it’s been said before: We have been dealing with several technical issues and what we’re doing now is we work the problem. We come up with a plan to fix that issue, and we work through that problem. This is a technical issue, it is complex, it has required a lot of testing, and it is taking longer than we expected and we understand the frustration from passengers. But we are working this problem and we will come to a technical solution as we have done with other technical issues on the line.
De Angelis is the director of investigations for rail and pipelines for TSB. The TSB has previously investigated issues related to the wheels on the LRT.
Q: [The vehicle axle bearing assemblies are failing well before 1.2-million kilometres.] What does that signal to you?
A: It signals the communications we’ve been seeing publicly, where it’s an acknowledgement that there is an issue, and the testing that is being done, hopefully, the expectation is that the testing will identify the root cause: why are there bearings not lasting as long as they were originally designed to last? Hopefully that report will shed some light and there will be some options presented and solutions that will be put forward so that the system will have that robust nature…
Q: Is it normal for a report to take almost two years to complete? (A reference to the “root cause” report on the August 2021 derailment from OC Transpo and its partners, which is expected to be delivered in September 2023.)
A: I think it perhaps highlights the complexity of this issue and the need for the information and the lengths that they’ll need to go to to determine the solution. From our standpoint in terms of our investigations, the more complex and investigation the longer the time it takes to produce. I’m assuming in this case; we’re not involved in the development of that report. I’m assuming that’s due to the complicated nature of the problem they’re trying to solve.
Q: Ontario’s Premier Doug Ford weighed into all this this week and said Ottawa’s LRT is “a real disaster”. How would you describe it?
A: We look at it from a safety perspective. Right now an issue has been identified, there’s an agreement about what the issue is, it’s the cartridge bearing assembly. There’s mitigations that have been put in place and this week highlights how important those mitigations are and how important those inspections are. Long term, as we said in the letter3, a long term solution is needed to minimize any of those safety risks, and in the meantime monitoring those bearings is a prudent form forward, a way that’s necessary to maintain and ensure safety.
At today’s media availability, official said it could take 12-18 months to design, test, and install new wheel hub assemblies on all 45 trains. In the meantime, OC Transpo is working with Rideau Transit Group and Alstom to come up with a plan to resume service safely with the current trains and wheels. More details are expected throughout the week.
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Council has had deep dives into the wheel assemblies at several Transit Commission and Light-Rail Sub-Committee meetings, and the issue was investigated at the LRT inquiry last year.
Far, far earlier: The trains are currently grounded because of potential problems discovered in an axle bearing during a routine 50,000km inspection.