Block instrument failure on an Absolute Block line

[Dieseldriver]

I’m a Driver but I’ve never worked trains over AB lines. In the S5 module of the rule book, it states that one of the occasions you may proceed at up to 50mph after passing a signal at danger with authority is during a failure of a block instrument on an Absolute Block line.
Obviously I understand how AB lines operate, I’m just curious as to why you are permitted to travel at up to 50 in that circumstance rather than at caution.

 

[bengley]

Without checking the signallers' rule book for AB I'm assuming there will be other safeguards in place between signaller A and signaller B.

Some AB sections can be many miles long (20+ in some places) so it's not something you'd want to be doing at caution.

 

[Snow1964]

Without checking, the key is the words with Authority
From memory wouldn't be given authority unless can proceed to next home signal (plus its overlap)

Clearly not going to be told to proceed at max 50mph if can't clear the signals as there is something unknown ahead, eg wires down where tree might have fallen.

 

[cin88]

If the line ahead is clear to the clearing point of the box in advance and said box has therefore accepted you then there's no need for a caution. You're simply passing the section signal at danger due to it being held by the block instrument being stuck at "Train on Line". The fault is simply with the Block Instrument rather than anything to do with the signals or track.

 

[Ken H]

If the block instruments fail but the bell works that can do. Or if there is a telephone that can be used to keep the block system going. Only if there is no communication between the boxes do they resort to time interval working, but that comes with a severe restriction that the driver must drive within what he can see.

 

[Llanigraham]

Althought the Block Instrunent might have failed (hopefully) the bells will still work, so before you will be allowed to pass the Section signal the signaller will know that the section is clear up to the clearing point of the Home signal at the next Box. Therefore your 50mph speed is perfectly safe.
We went through a whole spate of these on the Down from Bromfield to Woofferton Junct and no matter what S & T did it kept re-occuring. Eventually newer bits were acquired from the Severn Valley. The fault didn't re-occur before I retired.

It gets more "fun" when the bells fail as well, then everything is done over the phone and very carefully recording in the TRB. And yes we had that once!

 

[Ken H]

Althought the Block Instrunent might have failed (hopefully) the bells will still work, so before you will be allowed to pass the Section signal the signaller will know that the section is clear up to the clearing point of the Home signal at the next Box. Therefore your 50mph speed is perfectly safe.
We went through a whole spate of these on the Down from Bromfield to Woofferton Junct and no matter what S & T did it kept re-occuring. Eventually newer bits were acquired from the Severn Valley. The fault didn't re-occur before I retired.

It gets more "fun" when the bells fail as well, then everything is done over the phone and very carefully recording in the TRB. And yes we had that once!

Isnt there the possibility of using a public phone too?

 

[Llanigraham]

Isnt there the possibility of using a public phone too?

I suppose if the inter-Box line went down as well.

 

[The Lad]

Mmm, I have a recollection of using a coinbox phone to do just that, albeit on staff and ticket.
Long into history!

 

[Ashley Hill]

resort to time interval working,

Didn’t that disappear from the rule book in the 1990s?

 

[Llanigraham]

Didn’t that disappear from the rule book in the 1990s?

I don't recall seeing it in the Rule Book, nor being taught it at Signalling School, nor it ever being mentioned at the Quarterly Briefing tests.

 

[CAF397]

It was explained to me that it's an old rule regarding block failure, that the line side telegraph poles could've fallen on the railway. The 50mph restriction was a safety restriction.

 

[rower40]

If the lineside poles are already down, then running a train into them (especially a steam-loco-hauled train - bear in mind when these rules were written!) isn't going to cause a huge host of EXTRA work...

 

[Ashley Hill]

I don't recall seeing it in the Rule Book, nor being taught it at Signalling School, nor it ever being mentioned at the Quarterly Briefing tests.

I seem to remember it was still referred to I the 1988 rule book. Mainly to do with train failure and passing signals at danger.

 

[Tomnick]

My understanding is that it's a relatively recent change recognising that there's still a form of mitigation in that the Absolute Block mode of signalling will still be being observed between the two signallers (either by bell or by phone), and thus less risk of a train inadvertently being let into an occupied section.

There's still a risk of talking one past the section signal without the permission of the box in advance and/or with the previous train still in section, and presumably 50mph was chosen so as to still provide sufficient mitigation against this risk.

That said, in my experience, the block "failure" is more often than not merely a symptom of another fault!

 

[Efini92]

I’m a Driver but I’ve never worked trains over AB lines. In the S5 module of the rule book, it states that one of the occasions you may proceed at up to 50mph after passing a signal at danger with authority is during a failure of a block instrument on an Absolute Block line.
Obviously I understand how AB lines operate, I’m just curious as to why you are permitted to travel at up to 50 in that circumstance rather than at caution.

I think 50 is the magic number for degraded working. Not sure why they say 50 for TBW or SLW in the wrong direction either.

 

[Sunset route]

it

Didn’t that disappear from the rule book in the 1990s?

I don't recall seeing it in the Rule Book, nor being taught it at Signalling School, nor it ever being mentioned at the Quarterly Briefing tests.

I seem to remember it was still referred to I the 1988 rule book. Mainly to do with train failure and passing signals at danger.

I was taught “Time Interval Working” when I was at signalling signalling school in 1989 and I believe it was removed from the Signalling Regulations by 1992/93.

 

[MK88]

Without checking, the key is the words with Authority
From memory wouldn't be given authority unless can proceed to next home signal (plus its overlap)

Clearly not going to be told to proceed at max 50mph if can't clear the signals as there is something unknown ahead, eg wires down where tree might have fallen.

Incorrect. A block failure has nothing to do with something unknown ahead. Most of the time it's either some cut cables, stolen cables, or some cleaning needing to be done inside the block instrument.

Axle Counter Failure, TC Failure or Signalling failures are different to what the OP has said.