Comment by montroser
7 hours ago
What are the some of the ways that tracks are monitored for fractures like this? It must have been pretty substantial in order to be described as "complete lack of continuity". Makes me think of literally electronic continuity tests -- are those ever used in this context? Or how about cameras mounted on trains using image processing? Or drones?
It seems a shame that a few other trains passed beforehand with this anomaly in place and yet it went undetected.
Measurement trains filled with cameras and LIDAR
For example, in the U.K.:
https://en.wikipedia.org/wiki/New_Measurement_Train
https://en.wikipedia.org/wiki/Doctor_Yellow
LIDAR is good, but as another commenter pointed out, Ultrasonic Flaw Detection (USFD) is the gold standard for crack/flaw detection.
There are special trains with measurement equipment on board, but yes, it sounds to me like every train should be equipped with some basic sensors for anomaly detection.
The measurement trains drive slowly in the night.
Not necessarily, the measurement train my company develops can go up to 100 km/h and measure certain rail features every 5mm at that speed.
AFAIK, one technique for monitoring cracks uses ultrasonic sensors. They send sound waves through the rails and detect cracks by analyzing reflected waves.
Wheel Impact Load Detector.
It measures vertical forces in kips - (kilo-pounds-force, 1 KIP = 1,000 lbs)
They have these in the USA.
TFA indicates a 40cm gap — huge!
I suppose that counts/was caused by a fracture but almost a half meter of gap in the track is nuts. Like describing a limb that’s totally removed as a bone fracture.
Though conceivably the break was very small and a train impacting the slightly lifted rail just caused a good chunk of it to explode.
> Though conceivably the break was very small and a train impacting the slightly lifted rail just caused a good chunk of it to explode.
The crown (top) of the rail seems to be missing after the gap. The crown-less section then continues ~3 meters before it disappears behind the investigator on the left. IDK what that might indicate.
ref pic: https://ichef.bbci.co.uk/news/1024/cpsprodpb/ecb4/live/53924...
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Yes, the “fracture” (the problem was actually at a joint) was there for a while. The missing segment of rail was still there when the train arrived - the derailment affected only the last cars.
No, that gap was created after the rail broke and the train derailed as a result.
The crack was in the weld, causing one side to sink and the wheel to hit the start of the next section of rail which was no longer welded to it, causing stress fractures to form in the rail which later caused that 40cm piece to break off.