Ottawa LRT

[ijmorlan]

(aside from the fact that they seem to be fly paper for irresponsible drivers in SUVs)

That's actually funny. What sucks is that the Woolwich Observer cartoonist couldn't come up with something funny like this.

Are they ever funny?

[jeffster]

That's actually funny. What sucks is that the Woolwich Observer cartoonist couldn't come up with something funny like this.

Are they ever funny?

Touché....

[taylortbb]

https://ottawa.ctvnews.ca/mobile/lrt-tra...-1.5591616

The disaster of the Ottawa LRT keeps going, with an in-service derailment; the second in as many months. Previous one resulted in a 5 day system shutdown, and this one likely will too. I don't know whether to blame Alstom or RTG more, but one of them isn't doing their job. Damage doesn't look structural, but definitely beyond a minor event.

We're very lucky our LRT has gone better. I think there was a lot more skepticism here than in Ottawa about whether rail transit was really necessary. If ION had gone anything like this, the calls to rip it all up would be widespread.

   

[Bytor]

https://ottawa.ctvnews.ca/mobile/lrt-tra...-1.5591616

The disaster of the Ottawa LRT keeps going, with an in-service derailment; the second in as many months. Previous one resulted in a 5 day system shutdown, and this one likely will too. I don't know whether to blame Alstom or RTG more, but one of them isn't doing their job. Damage doesn't look structural, but definitely beyond a minor event.

We're very lucky our LRT has gone better. I think there was a lot more skepticism here than in Ottawa about whether rail transit was really necessary. If ION had gone anything like this, the calls to rip it all up would be widespread.

What do we know about track geometry and speeds where the derailments happened? Or the wheel shape conical section specs?

[KevinL]

Some punditry I've seen says the speeds they're hitting aren't a good fit for low-floor trains, and that the technology choice there is the root of the problem. Certainly there's little need for low floors on this system as it exists.

[danbrotherston]

Some punditry I've seen says the speeds they're hitting aren't a good fit for low-floor trains, and that the technology choice there is the root of the problem. Certainly there's little need for low floors on this system as it exists.

To be honest I've never understood what the big deal about low floor vehicles is. For most systems that are entirely separated, as Ottawa and our systems are there should be no reason that you cannot have platforms at a higher level for traditional lrvs so I don't really understand why the low floor vehicles are so sought after.

I also get that because of the design of the bogies their maneuverability is restricted in some ways, but I wouldn't think that speeds are the problem. Our system attains 70k an hour. Does Ottawa system obtain significantly higher than this?

[jamincan]

It's a legacy of planning prior to the Confederation Line that would have resulted in a mix of street-running on grade-separated rail. I don't think there is any plan for street-running anymore, but at the time I believe they wanted to leave that possibility open.

[ac3r]

It's basically a light metro rather than light rail (even though the LRTA doesn't define it as such), so this particular rolling stock on this line wasn't needed. I suppose they probably already ordered low floor vehicles and weren't able to back out of that though. It blows the ION out of the water due to the underground and grade separated infrastructure, but the vehicles seem to be horrible.

[danbrotherston]

It's a legacy of planning prior to the Confederation Line that would have resulted in a mix of street-running on grade-separated rail. I don't think there is any plan for street-running anymore, but at the time I believe they wanted to leave that possibility open.

"Street-running" can mean many things, our LRT is street-running but the stations are still extensive enough to permit a high-floor LRV. The only thing that really demands a low floor LRV is literal street level boarding a la TTC streetcars.

[jeffster]

https://ottawa.ctvnews.ca/mobile/lrt-tra...-1.5591616

The disaster of the Ottawa LRT keeps going, with an in-service derailment; the second in as many months. Previous one resulted in a 5 day system shutdown, and this one likely will too. I don't know whether to blame Alstom or RTG more, but one of them isn't doing their job. Damage doesn't look structural, but definitely beyond a minor event.

We're very lucky our LRT has gone better. I think there was a lot more skepticism here than in Ottawa about whether rail transit was really necessary. If ION had gone anything like this, the calls to rip it all up would be widespread.

What do we know about track geometry and speeds where the derailments happened? Or the wheel shape conical section specs?

Unsure of the track geometry but I heard this was a low speed derailment.

[Bytor]

What do we know about track geometry and speeds where the derailments happened? Or the wheel shape conical section specs?

Unsure of the track geometry but I heard this was a low speed derailment.

Derailments at low speeds are usually penultimately caused by two things.

The obvious one is when the vehicle itself lurches to the side, so the wheel bogie is lifted up enough that the flange on the wheel no longer prevents it from moving laterally.

The less obvious one is when the tracks are misaligned in some fashion that causes the flange to touch the rail in such a way that the friction from this new contact patch basically levers the wheel up past the flange and laterally out across the rail. The lighter the load on the wheel, the less friction is required for this to happen. Track shift around a curve can cause this by making the effective curve radius tighter than it should be and this increases friction. Or it can be caused by track twist that unloads a wheel and requires less friction to make it jump. A third cause is worn wheels with a reduced flange angle which increases the size of the flange's contact patch going around a curve which increases the friction. 

There's a lot of math and physics involved in this, beyond my ability to explain it more in depth than this, but if you are interested you can look up "Nadal's Criterion" (sometimes "Formula"), which is what this is. It's one of the things used to determine what the minimum curve radius for locomotives and cars of a given weight going at a specific speed. The related Wagner's Formula takes into account hunting oscillation at higher speeds.

Since the picture shows the whiles outside the track, we can rule out a gauge-widening misalignment, which would cause the wheel to fall of the rail to the inside.

So we're left with two likely ultimate causes.

The first is that the wheel sets are badly maintained and not being properly monitored for wear to the flange angle. At low speeds there shouldn't be any hunting oscillation and the flanges should never contact the rails on straight segments, but worn wheel sets will start to oscillate a lower speeds which will cause greater flanging friction around curves, but also potentially (but hopefully rarely) on straightaways. 

The second is bad track construction and or maintenance that has let the tracks go out of alignment resulting in higher frictions that violates Nadal's Criterion to keep the wheel from jumping. Unexpectedly high flanging forces can cause tracks to go out of alignment, but even with worn wheels that's AFAIK only at higher speeds that can do that, though tamping the rails can apparently reduce their ability resist lateral displacement.

[panamaniac]

The Citizen is reporting that the system could be out of operation for up to 3 weeks. The cause may have been a bracket that came loose on the device that holds the sand for winter traction.

[taylortbb]

https://ottawa.ctvnews.ca/mobile/o-train...-1.5601397

O-Train shutdown enters second week as investigation continues into Sept. 19 derailment

[...]

Last week, the Transportation Safety Board of Canada said the LRT train actually derailed before entering Tremblay Station, approximately 500 metres from the station.

"The train then departed the station in the derailed condition and continued over the rail bridge that traversed Riverside Drive before striking a signal mast and switch heater that were adjacent to and north of track 1," said the TSB.

How did a train travel over 500m while derailed without the driver noticing and stopping? Or a passenger noticing? It seems like something that would make for a bumpy ride.

[ijmorlan]

How did a train travel over 500m while derailed without the driver noticing and stopping? Or a passenger noticing? It seems like something that would make for a bumpy ride.

And how did it maintain an electrical circuit with the wheels off the tracks?

[danbrotherston]

How did a train travel over 500m while derailed without the driver noticing and stopping? Or a passenger noticing? It seems like something that would make for a bumpy ride.

And how did it maintain an electrical circuit with the wheels off the tracks?

I assume not all the bogies derailed, I'm unsure of how exactly the power systems work on the train, but I can see it maintaining power in that situation.