Track Circuits and broken rails

[Deleted]

There is one possible downside relying on TBTC, the broken rail detection protection facility provided by track circuits is no longer available, once the old signalling is decommissioned. Has this been considered???

[Deleted]

Jun 27, 2017 20:46:06 GMT @kkc35348 said:

There is one possible downside relying on TBTC, the broken rail detection protection facility provided by track circuits is no longer available, once the old signalling is decommissioned. Has this been considered???

That was raised at the time but nobody could provide evidence where broken rails had actually been detected by track circuit failure. Ultrasonic testing and track inspections usually identify this. I'm not a track expert but I would think that most issues are cracked rails rather than completely broken rails and a cracked rail would presumably still pass the track circuit current?

At the risk of tempting fate, TBTC has been in service on the Jubilee line for 6 years now and I'm not aware of any incident where a broken rail went undetected.

[North End]

Jun 28, 2017 7:30:00 GMT @tridentalx said:

Jun 27, 2017 20:46:06 GMT @kkc35348 said:

There is one possible downside relying on TBTC, the broken rail detection protection facility provided by track circuits is no longer available, once the old signalling is decommissioned. Has this been considered???

That was raised at the time but nobody could provide evidence where broken rails had actually been detected by track circuit failure. Ultrasonic testing and track inspections usually identify this. I'm not a track expert but I would think that most issues are cracked rails rather than completely broken rails and a cracked rail would presumably still pass the track circuit current?

At the risk of tempting fate, TBTC has been in service on the Jubilee line for 6 years now and I'm not aware of any incident where a broken rail went undetected.

Whenever I've experienced a "broken rail" it has usually been a blockjoint which has broken in two. TBTC does have the advantage of eliminating these.

It's worth adding that the mainline railway doesn't seem to deem broken rail detection important. Many miles of absolute block signalling have no train detection at all, whilst most new schemes use axle counters.

[Chris M]

Jun 28, 2017 7:30:00 GMT @tridentalx said:

Jun 27, 2017 20:46:06 GMT @kkc35348 said:

There is one possible downside relying on TBTC, the broken rail detection protection facility provided by track circuits is no longer available, once the old signalling is decommissioned. Has this been considered???

That was raised at the time but nobody could provide evidence where broken rails had actually been detected by track circuit failure.

Not what is usually meant by a broken rail, but in 2006 a rail on line open to traffic near Thirsk was cut and removed -
RAIB report.

Paragraph 6 of report:

At 23:35 hrs on the 11 January 2006 a gang of track workers started to remove a rail from the down slow on the approach to Y427 signal, just to the North of Thirsk station. As a consequence of this action a track circuit was interrupted causing it show as occupied. Subsequently, train 1P64, the 21:22 hrs Manchester Airport to Newcastle, was held at signal Y423 which could no longer be cleared due to the track circuit showing occupied. It was then discovered that the rail had been severed on a line that was still open to traffic and was in the process of being removed (ie the worksite had been established outside of an engineering possession).

Obviously the underlying cause of this was failures in the work planning process, but the consequences of the failure were less severe because of track circuits.

[Deleted]

Jun 28, 2017 7:30:00 GMT @tridentalx said:

Jun 27, 2017 20:46:06 GMT @kkc35348 said:

There is one possible downside relying on TBTC, the broken rail detection protection facility provided by track circuits is no longer available, once the old signalling is decommissioned. Has this been considered???

That was raised at the time but nobody could provide evidence where broken rails had actually been detected by track circuit failure. Ultrasonic testing and track inspections usually identify this. I'm not a track expert but I would think that most issues are cracked rails rather than completely broken rails and a cracked rail would presumably still pass the track circuit current?

At the risk of tempting fate, TBTC has been in service on the Jubilee line for 6 years now and I'm not aware of any incident where a broken rail went undetected.

Try the Central Line a couple of years ago

A track circuit failure JTC FS2500 came in during the late afternoon peak upon inspection the fault was outside with a low MPV Monitor Point Voltage coming back into the room and on closer examination it was found to be caused by a broken rail.

Track Circuits are designed to detect trains finding a broken rail or missing rail is a by product of it.

[norbitonflyer]

Jun 28, 2017 11:38:24 GMT Chris M said:

Not what is usually meant by a broken rail, but in 2006 a rail on line open to traffic near Thirsk was cut and removed -

Something similar happened at Staplehurst in 1865, leading to the derailment of a boat train. The incident was described by one of the passengers - a certain Mr Charles Dickens, who survived the accident (as did the manuscript of "Our Mutual Friend") but suffered what we would probably now recognise as post-traumatic stress disorder.

In a postscript to the book, he wrote
"On Friday the Ninth of June in the present year, Mr and Mrs Boffin (in their manuscript dress of receiving Mr and Mrs Lammle at breakfast) were on the South-Eastern Railway with me, in a terribly destructive accident. When I had done what I could to help others, I climbed back into my carriage — nearly turned over a viaduct, and caught aslant upon the turn — to extricate the worthy couple. They were much soiled, but otherwise unhurt. [...] I remember with devout thankfulness that I can never be much nearer parting company with my readers for ever than I was then, until there shall be written against my life, the two words with which I have this day closed this book: — THE END."

He died on the fifth anniversary of the accident.

omf.ucsc.edu/dickens/staplehurst-disaster.html

[Deleted]

Jun 28, 2017 13:55:12 GMT @aetearlscourt said:

Try the Central Line a couple of years ago

A track circuit failure JTC FS2500 came in during the late afternoon peak upon inspection the fault was outside with a low MPV Monitor Point Voltage coming back into the room and on closer examination it was found to be caused by a broken rail.

Track Circuits are designed to detect trains finding a broken rail or missing rail is a by product of it.

Interesting, thanks. I'd not heard of a confirmed example. Any more detail on this please? Was the rail completely snapped or just cracked?

[Deleted]

Snapped but of course the 2 parts were just about touching hence the voltage was still present upon testing

[Tom]

I can only think of one broken rail that was found by a track circuit, and like the example DistrictSOM mentions it was an intermittent track circuit failure.

The other two I remember seeing were both undetected by the track circuit; one was around a fishplate which naturally was bonded. It's worth remembering that London Underground generally uses single rail track circuits so that in the event of the break being in the continuous rail, there is no guarantee of detection.

Even on the section rail in points and crossings areas there is the possibility of a break not being detected, especially if it's on a limb or spur.