Foul Tracks

[mailmesashi]

Hi,

I have a query related to foul tracks.

General definition of foul tracks states that these are  to be proved directly in the signal aspect controls, to

confirm that any unauthorised movement foul of the route replaces the signal. But, if the POP groups are defined for that scheme, then this unauthorised movement will be detected as an overrun. In such cases, is it required to include foul tracks in the aspect level.

Thank You.

[PJW]

Hi,

I have a query related to foul tracks.

General definition of foul tracks states that these are  to be proved directly in the signal aspect controls, to

confirm that any unauthorised movement foul of the route replaces the signal. But, if the POP groups are defined for that scheme, then this unauthorised movement will be detected as an overrun. In such cases, is it required to include foul tracks in the aspect level.

Thank You.

Good question- what do you think is the best answer?
It might be a good one for IRSE to ask in the exam ...........

If you are actually asking what is the answer that adherence to RGS and NR standards would suggest, then the simple answer would be yes.
The reason why I say that is that compliance to the standard that used to be GK/RT0060 (now transferred to NR's Signalling Principles & Application Handbook) demands it.  
However I do not believe that this has been considered for revision since the implementation of overrun protection in the control system.  Therefore although it states what it does, it is worth considering if it still should........

There are certainly some arguments that it should be retained-
A) control system is at best SIL2
B) the foul track could be occupied without route cancellation via POP group having occurred (e.g. The signaller could deliberately or by error left a "SPAD inhibit" applied incorrectly)
C) the foul track could be occupied by a vehicle moving where it should not when working within a possession- this vehicle may always have been beyond the protecting signal and thus no SPAD for the SPAD detection to register and initiate POP Group.

Conversely there are some arguments that it should be removed from the requirements; can you think of any?

Like much in signalling, it is a balance and opinions will differ.  Think about what risk the control is intended to mitigate, make an assessment of likelihood and severity without the mitigation and with the mitigation.  Consider the costs of the mitigation and indeed the other effects and associated costs including those due to reduction in various RAMS metrics).  Determine the optimum balance of the various risks; if having done this you are certain that it is beneficial NOT to include foul tracks in the aspect then word your derogation application, support it with safety argument and see if you can convince others.
 



.

[Rob]

I was not sure what a POP group was.

POP group - Predetermined Overrun Protection group
"A group of signals replaced to danger by the signalling system after a SPAD: the grouping is agreed in advance in consultation with operational specialists."
"NR/L2/SIG/30009/E421 describes the extent of the required predetermined protection for each signal"
Ref: NR/L2/SIG/30009/E420 Issue 2, March 2015

I understand it is an automatic reaction to a SPAD as part of overrun management implemented in the control system (i.e. IECC) rather than the interlocking to reduce complexity in the interlocking ('simpler is safer') and to reduce cost (~SIL 2 cheaper than ~SIL 4).

[PJW]

I was not sure what a POP group was.

POP group - Predetermined Overrun Protection group
"A group of signals replaced to danger by the signalling system after a SPAD: the grouping is agreed in advance in consultation with operational specialists."
"NR/L2/SIG/30009/E421 describes the extent of the required predetermined protection for each signal"
Ref: NR/L2/SIG/30009/E420 Issue 2, March 2015

I understand it is an automatic reaction to a SPAD as part of overrun management implemented in the control system (i.e. IECC) rather than the interlocking to reduce complexity in the interlocking ('simpler is safer') and to reduce cost (~SIL 2 cheaper than ~SIL 4).

Yes that just about sums it up.  POP Groups is an awful name as at least one of the people who were very involved in writing E420 never tires of saying; they fought valiantly against it but were overwhelmed.

I actually don't think that it makes a huge amount of difference doing in control system or interlocking; ironically it can be easier to amend interlocking data!  However it does mean that it removes it from the  province of Principles Testers (for good or ill) and certainly makes it easier spanning boundaries, particularly as we are now getting ROCs with a right mixture of CBI and RRIs of various different standards.  However the main thing is that the computer does what it does best (continually and tirelessly monitor for pre-defined scenario and quickly and reliably implement the pre-defined emergency response) but leaves the signaller to do what the human does best (use diverse sources of evidence and information to decide the best course of action in the particular circumstances).  
The main problem with the previous approach was the determination to impose pre-defined locking and because there are actually a range of scenarios (slight misjudgement, one wheel just past signal and train stopped, train continuing unchecked, train authorised to pass signal at danger but signaller had forgotten to place a SIS- SPAD Inhibit Short, no SPAD at all but just an unfortunately timed track failure) this was impossible to get right for all the different circumstances.  Compounded by the fact that it was implemented by "upside down route locking" which was invisible to signaller and little bits of it could be left lurking afterwards causing mystery failures of signals to clear).

[mailmesashi]

Hi,

I have a query related to foul tracks.

General definition of foul tracks states that these are  to be proved directly in the signal aspect controls, to

confirm that any unauthorised movement foul of the route replaces the signal. But, if the POP groups are defined for that scheme, then this unauthorised movement will be detected as an overrun. In such cases, is it required to include foul tracks in the aspect level.

Thank You.

Good question- what do you think is the best answer?
It might be a good one for IRSE to ask in the exam ...........

If you are actually asking what is the answer that adherence to RGS and NR standards would suggest, then the simple answer would be yes.
The reason why I say that is that compliance to the standard that used to be GK/RT0060 (now transferred to NR's Signalling Principles & Application Handbook) demands it.  
However I do not believe that this has been considered for revision since the implementation of overrun protection in the control system.  Therefore although it states what it does, it is worth considering if it still should........

There are certainly some arguments that it should be retained-
A) control system is at best SIL2
B) the foul track could be occupied without route cancellation via POP group having occurred (e.g. The signaller could deliberately or by error left a "SPAD inhibit" applied incorrectly)
C) the foul track could be occupied by a vehicle moving where it should not when working within a possession- this vehicle may always have been beyond the protecting signal and thus no SPAD for the SPAD detection to register and initiate POP Group.

Conversely there are some arguments that it should be removed from the requirements; can you think of any?

Like much in signalling, it is a balance and opinions will differ.  Think about what risk the control is intended to mitigate, make an assessment of likelihood and severity without the mitigation and with the mitigation.  Consider the costs of the mitigation and indeed the other effects and associated costs including those due to reduction in various RAMS metrics).  Determine the optimum balance of the various risks; if having done this you are certain that it is beneficial NOT to include foul tracks in the aspect then word your derogation application, support it with safety argument and see if you can convince others.

hi,
Thanks for the reply.
I vote for the inclusion of the Foul tracks. As per my understanding, eventhough the chance of two incidents/scenarios's may not happen at the same time(i.e unauthorised move and SPAD inhibt latch set/left over mistakenly), I strongly go to have the foul track in the aspect level, as a preventive measure. Guide me, if thats leads to a wrong corner, please.

[mailmesashi]

Hi,

Another quick question/doubt. Does the Conrol centre has SPAD inhibit latch, if POP groups are involved. If not, will there be anyother option for signaller to initiate inhibition.

Thank You.

[Thed1983]

thanks a lot for the tons of useful information i found here. would you people mind if i am going to ask some questions in the future? i ask this because i'm too anxious to ask real people (i even take klonopin, that's how anxious i am) please and thanks!!