In April, a train derailed on the Cape Breton & Central Nova Scotia Ry between Truro and Sydney, Nova Scotia. Evidently this line still has banked curves from the days it ran passenger trains.
In the formal accident report the “steep banking of the curve” was deemed the main cause of the derailment, and this was verified by RailAmerica. The report also mentioned that some ties had deteriorated.
I’ve seen several articles on derailments that mention deteriorated track structure, out of gauge, etc. but I don’t recall ever seeing “steep banking of the curve” as a main cause.
I can… the inside rail can start to turn over as the weight transfers onto it. I’ll bet the derailment was on the low side, not the high side. This would logically relate to an observation about ‘deteriorated ties’ in the report if the cause is explicitly understood to be caused by ‘high’ superelevation.
Superelevation could also cause problems if the load shifts, or the roll center of the load is high and other track defects or running conditions cause the car to start rocking side to side (in which case I’d expect it would derail or fall over toward the inside of the curve). Sudden run-in of slack might also precipitate this sort of problem on the high rail, as it’s relatively lightly loaded compared to the situation on a ‘flat’ curve, and this might translate into lifting a wheel or allowing an axle to **** more readily relative to its sideframes.
Be interesting to find out what the max degree of superelevation on this line might be.
It has to do with how steep the elevation is and where the load of the train gets placed on the rail.
Done right, superelevation keeps the flanges off the inside edges of the rail, so all the load is distributed from the wheel tread to the railhead. Too much or too little elevation and the flanges transfer load to the inside edge of the rail, and eventually the rail either overgauges (dropping a wheel on the ground) or rolls over (dropping a wheel on the ground).
This segment of CBNS hasn’t seen a lot of maintenance snice takeover from CN in 1993-94, and I think the elevation was at the limit of tolerance to begin with.
Thankyou ericsp for explaining what that means. My only question than is why is it like that? If there are speed restrictions on that kind of track section (I don’t know if there is), why would the track be banked unless it was for high-speed trains turning into the curve?
Banking curves allows the train (or vehicle for roads) to travel faster for a curve of a given radius. The reason why it does is that while the train is on the curve, part of its weight is directed towards the center of the curve. Unfortunately, this puts more stress on the inside rail, which means the inside rail is more likely to roll. Also, if the train is moving too slow, the superelevation is too steep, and/or a high center of gravity car (covered hopper for example) the superelevation can cause a car to turn over. I should clarify that if the superelevation is shallow, it would probably be impossible to derail a hopper due only to the superelevation.
In this case there were 10 cars, including 6 tank cars with propane or butane. The area was marshy so the cars were cushioned after the track gave way.
Bentnose Willie’s comment about “limit of tolerance” was mentioned too. The super-elevation was just within the spec
The article was published 9/14/04 in the GlobeandMail.com so an on-line search might work. I tried to copy the link but couldn’t get it to work.
They had committed $500K for lowering the super-elevation on several curves on the western section of the track. That and fixing the rotten ties (and keeping the track in gauge!) should do it.
Two cents worth… maybe… from my reading of the article, it sounded very much as though the derailment happened to the inside of the curve. There are several ways this can happen – as usual, I think I agree (without access to all the facts, so 'most any opinion is at least partly speculation!) with overmod – the comment about the ties suggests that the side load on the inside rail pulled the rail over. Having seen that track a few years ago, I can believe it… In general, though, if the superelevation is too high for the train’s speed, cars can literally fall off the inside, too – particularly covered hoppers and some types of tank cars, which get to really rocking at certain speeds. Another way to get a derailment on a curve is ‘stringlining’ – when the tractive forces in the train are high enough to literally pull a car or two in towards the centre of the curve. This is particularly a problem when you have empties up front and loads behind, and are going up hill or otherwise taking the slack out.
MP57313 – the folks who own the property are in the process of upgrading the whole thing and resurfacing for lower track speeds.
As already mentioned, superelevation is done on roads too. For an extreme example, look at a hippodrome - where they ride motorcycles inside a cylinder.
Gravity is one factor, the other is centrifugal force. Think of a race track. The curves are banked to help the race cars stay on the track. They wouldn’t be able to hit speeds of over 150 mph on the curves if they were flat.
If a curve is designed to handle a high-speed limited, it will be superelevated. In theory the centrifugal force will balance with gravity, and as mentioned, the treads of the wheels will center up on the head of the rail and the flanges will be a relatively minor player, minimizing wear.
However, just as you wouldn’t want a 25 mph city street banked like turn 3 at Daytona, you don’t want a low speed freight track extremely superelevated. The automobiles might not roll over on said street, but the high-centered semi’s probably will. That phenomenon appears to have been a factor in the subject derailment.
Passenger train curves have been known to be superelevated up to 8 inches on standard gauge. Freight trains rarely need superelevation above 4 inches and run at lower speeds. Those freight trains have a lower unbalance speed (FRA or TCA) than passenger trains because the loading and center(s) of gravity are anything but uniform. TILT!
No… all you need to do is flatten out the curve, unless your operating ALL your trains at high speeds super elevation is a liability. Cars like hoppers and tank cars have a high center of gravity, you don’t have to tip them very far before they fall over, I recall a derailment we had near Bardwell jct. on the WICT because of exactly this. We flattened the curves ASAP.
Randy
Junctionfan – various kinds of safety rail systems are as old as the hills. The principal problem with ‘roller-coaster’ type systems as I assume you mean them (aside from much higher capital and maintenance cost) is in the difficulty switching vehicles and in accommodating worn track profiles or subsidence. Very theoretically you could address problem #1 with an analogue of Alweg flexible-beam switching, and the second by using a relatively lightweight elevated structure… or even a full monorail sort of arrangement. But these things cost far, far more than the value of service would ever justify… and, of course, the reduction of risk of derailment from a cause this sort of system would avoid is infinitely less cost-effective than a reduction gained by plowing the money into proper lining,surfacing, wear maintenance, etc.
I was waiting to see if anyone addressed the guard-rail question you had in an earlier post – the reason for guards on bridges is because any derailed truck must be kept from getting sideways and spilling the train. On a curve, the effect of a wheelrim jamming down into that spece isn’t going to help matters that much – and your rail expense, along with the expense of laying that rail (etc.) will go up dramatically — again, with little to show for the expense objectively.