Answer to 2005 Part A Q1

[alexgoei]

Hello Peter,

Appended please find my answer to the 2005 Part A Q1. Would appreciate it if you can go through it and let me have your comments.

I have two questions which I hope you can provide answers to:

1 What is current Network Rail practice with respect to overlaps for shunt routes. Previous postings on this website suggest Yes to overlaps for shunt routes as well. For Shunt routes do they have full and restricted overlaps?

2 In this paper, the notes on the layout states that "Calling On signals on 131, 144, 145 and 146 are running round only." Could you illustrate these movements on the schematic please? I have some problem visualising these moves.

Look forward to your reply.

Thank you & Regards

[PJW]

Hello Peter,

Appended please find my answer to the 2005 Part A Q1. Would appreciate it if you can go through it and let me have your comments.

I have two questions which I hope you can provide answers to:

1 What is current Network Rail practice with respect to overlaps for shunt routes. Previous postings on this website suggest Yes to overlaps for shunt routes as well. For Shunt routes do they have full and restricted overlaps?

2 In this paper, the notes on the layout states that "Calling On signals on 131, 144, 145 and 146 are running round only." Could you illustrate these movements on the schematic please? I have some problem visualising these moves.

Look forward to your reply.

Thank you & Regards

Just to let you know that it has been a Bank Holiday weekend in the UK marking the end of the British summer so have been away- I aim to catch up the backlog soon!

1. NR stated current practice is to provide overlaps for shunt routes. However to do so is obviously rediculous when the shunt route does not prove all tracks in line of route clear (since in many cases of a shunct route there is a need to get a train to attach to another or a loco to attach to vehicles). Hence in modern jobs the same shunt route actually exists in 2 flavours; there tends to be an automatic selection based on state of occupancy of one or more track sections and thus either the shunt comes as "non-permissive" either an overlap or "permissive" without one since we know there is a train there. Whereas often only 1 route on the plan there are actually 2 different ones in data and CTs.

However I would NOT advise this policy for IRSE exam;
a) it is more work to do in the time, b) the scheme plan may not have envisaged shunts being given overlaps,
c) the examiners would be keener that you demontrate your understanding of the different nature of shunt and running movements.
Hence firm recommendation is DON'T GIVE SHUNT ROUTES OVERLAPS; state your practice is "late 20th century UK Mainline" or "Railtrack" or "current NR with exception of shunt overlaps and Robust Train Protection".

Don't get hung up on needing to do everything to the latest fashion- this is not what the exam is about. I have made reference to them in some replies because I believe that many read and I don't want to mislead them if that is what they have grown up with. To make it clear: unless CTs to absolute recent practice are your day job and it has become automatic for you, I see no rational reason in the exam for providing shunt overlaps but if the layout really suggests them as an expectation then you should definitely state your practice is not to provide.

Shunts only have one overlap; PL aspect means "proceed as far as the line is clear at a speed at which you can stop on sight of an obstruction, no more than 15mph"- there is no equivalent of a delayed Yellow and it would be a nonsense with that definition. There is certainly no need for an O/L longer than a ROL and thus if providing a shunt overlap use the shortest one that exists on the layout otherwise; i.e. if there is a (W) to same destination then use its ROL for the (S), if not use the normal O/L. You'll not find this written down anywhere but is purely common sense, though some real projects don't display that rare commodity I am afraid!


2. It really is not very clear to me. I interpret as saying loco pulls freight from terminal and leaves train on the Up Branch. Loco detaches and gets PL aspect which permits it to get behind 131 or 145 (even if those platforms happen to be occupied by other trains) so that loco can use the Down Branch Loop to run around and be signalled using 155 and 156 to rejoin and couple before pulling train in Down direction along the branch to A. On its return journey the train would surely be signalled up to 144 put then the PL on 157 used to authorise the propelling back into the terminal. Perhaps we also have to assume that some freight runs to C and thus the exit is easy but the return working has to be signalled up to 157, loco detach and be signalled via 157, 156, 146 to get behind 131 / 145 as applicableto get back onto train on Up Branch Loop before propelling back inside the facility.

I am not sure that the Signalling Plan note is very helpful and I would certainly argue that the PL moves from 144 / 146 in this circumstance should have been designated (S) rather than ©. Indeed since no MARI are provided with the PLs this reinforces my view provision of route indicator for a © was at the time of the paper mandatory though has subsequently been relaxed). I also personally am not very comfortable with M/C routes on passenger railway that are not applicable to passenger trains- to be a run around to join a loco back on its own train is definitely SHUNTING, not a CALL-ON that I regard as applying to 2 different trains that may be joining into one but which may remain totally separate.

Basically I agree with you the presentation is unnecessarily confusing; to provide call-ons rather than shunts and then add a note that effectively states they are used a shunts not call-ons is bizarre. We certainly wouldn't do that on "God's Wonderful Railway" but I think the person who drew the plan came from further north and perhaps their tradition differs and we need to respect all cultural heritage even if it differs from our own.........However we might feel like saying it, it is no longer politically correct to say "There are 2 ways of doing a job, the GWR way and the wrong way".

PJW

[PJW]

Herewith my comments on 2005 Control Tables.

These come to you by courtesy Of Westinghouse Rail Systems Limited who arranged for me to spend most of Saturday in Derby Power Signalbox as a fringe to the commmissioning of the Erewash / Chesterfield area of the East Midands Control Centre, but actually there was little for me to do ......

PJW

[PJW]

Herewith my comments on 2005 Control Tables.

PJW

I have also shown my comments on amended copies of your originals, hopefully to make things clearer

I judge the attached are a suitable compromise between tolerable size and reasonable resolution

[greensky52]

1 146C(M) routes to Down Main, but it requires 210A R, so is it still the opposing signal of 107? I feel I do not know the exact definition of opposing signal? It seems there is an overlap locking,is it overlap locking between 146C(M) and 107?

2 I remember in indirect route locking, if signal-A is parallel with another signal-B, and they have the same exit, then if B is direct opposing signal of signal C, A is indirect opposing of C. So, I think in 146A(M), 131B(M),131B©,127B(M) need to be route locking. Right or wrong?

3 In 128A(S), why does it need 107A(M) in route locking? I think it does not belong to any of these situation:overlap locking, direct opposing locking, indirect opposing locking....

[PJW]

1 146C(M) routes to Down Main, but it requires 210A R, so is it still the opposing signal of 107? I feel I do not know the exact definition of opposing signal? It seems there is an overlap locking,is it overlap locking between 146C(M) and 107?

Yes because 107 can have an overlap over 210 reverse as denoted by the overlap symbol which includes BD and 211B but excludes BE. 107 authoorises a train to proceed up to 127 whereas 146 authorises a train as far as 118 so it is definite that only one of the two routes can be set at the same time. Note that there is no overlap beyond 118 over 205N so in that direction the point locking is sufficient, 107 locking 205N whereas 146 requires 205R. The same is NOT true in the opposite direction, due to the fact that there is an overlap beyond 127 with either lie of 210.

So you are right that you have not yet correctly understood opposing route locking. Look at this thread for discussion of opposing signals and also this one for a short presentation that may be useful.

Also my write up on Control Tables can be found here and there is quite a bit on opposing locking there

2 I remember in indirect route locking, if signal-A is parallel with another signal-B, and they have the same exit, then if B is direct opposing signal of signal C, A is indirect opposing of C. So, I think in 146A(M), 131B(M),131B©,127B(M) need to be route locking. Right or wrong?

You are correct that having decided that signal A is directly opposing signal C then you need to CHECK WHETHER signal B is indirectly opposing. It will be IF the point locking is insufficient; it is NOT shown as indirectly opposing if the locking is achieved by point locking. In the cases you list routes from 127 or 131 hold 211 reverse until train clears BD at which time 146A(M) can be set safely. The point availability test of 211 normal or free to go is adequate and therefore the opposing is not shown (even if it is actually present in circuits or data) as it is actually superfluous (= additional to that which is truly needed as it only duplicates the more fundamental locking). You do need to get your head around this; see item 1.

3 In 128A(S), why does it need 107A(M) in route locking? I think it does not belong to any of these situation:overlap locking, direct opposing locking, indirect opposing locking....

128B(S) is obviously directly opposing to 107A(M) and hence shunt can only set if the Down train has been timed to stand in platform. Regarding 128A(S) it does depend upon how the interlocking as a whole is designed; there must be SOME locking preventing 107A(M) with 210R being set simultaneously with 128A(S) but there are DIFFERENT WAYS of achieving this aim.

Personally I'd set and lock 215N whether 210N or 210R and hence achieve that way via pseudo point-to-point rather than route locking.
Similarly I'd make 128A(S) set and lock 210 N (again pseudo point-to-point giving trapping) and therefore that would also prevent.
However unless the CTs achieve by point locking, then would have to achieve via route locking.

It is always a bit dangerous just to focus on one element of the locking shown on a set of CTs because it is INTERLOCKING and you do need to consider the overall picture as well as looking at the various pieces of the jigsaw by themselves.
In the Exam an additional complication is that candidate does not do a full set of CTs and therefore the examiner has sometimes to judge an attempt without knowing for sure how the CTs not requested would have been completed; they can only assume that would be consistent with those CTs that were done. Of course in the exam the candidate does have the option when doing a particular CT to state an assumption re what the relevant portions of another CT would have shown.

You are doing the right thing trying to work out what is right, what is wrong and why- however it does suggest to me that you are not fully grasping the "big picture" and seeing where it all fits together.

[greensky52]

After reading the notes carefully, I think I have known the route locking principle, including direct and indirect. I would like to practice it in further work.

But still have confusion about 128A(S): I did not understand your statement well. If 107A(M)'s swinging overlap locks 210A N and 215B N, then as soon as it clear its overlap-EM, 215B can be set to R for 128A(S), but now, the train routed from 107 does not head on 128A(S). Why do you still consider 107A(M) in 128A(S) route locking?

Yeah, I agree with you, I think sometimes I did not grasp the point of them, just remember the principle, but not really comprehend them because of the poor reading of Eng. There is not too much time for the exam, I feel great pressure....

Thanks a lot.

[PJW]

There is not too much time for the exam, I feel great pressure....

Thanks a lot.

You are not alone; I suspect a lot of people are also working frantically. Just don't drive yourself too hard at the last minutes or you won't be able to perform well in the exam as too tired and everything will fall to bits

[greensky52]

But still have confusion about 128A(S): I did not understand your statement well. If 107A(M)'s swinging overlap locks 210A N and 215B N, then as soon as it clear its overlap-EM, 215B can be set to R for 128A(S), but now, the train routed from 107 does not head on 128A(S). Why do you still consider 107A(M) in 128A(S) route locking?

And another question: how do you jusitfy the length of TC, such as BE, BF. I can only find their total length is 450m, but can not know its own length, having difficulty in calculating the approach control time .

There is not too much time for the exam, I feel great pressure....

Thanks a lot.

You are not alone; I suspect a lot of people are also working frantically. Just don't drive yourself too hard at the last minutes or you won't be able to perform well in the exam as too tired and everything will fall to bits

[PJW]

But still have confusion about 128A(S): I did not understand your statement well. If 107A(M)'s swinging overlap locks 210A N and 215B N, then as soon as it clear its overlap-EM, 215B can be set to R for 128A(S), but now, the train routed from 107 does not head on 128A(S). Why do you still consider 107A(M) in 128A(S) route locking?

The swinging overlap will NOT lock the facing points 210, but it would definitely lock (as trailing points in the overlap) 215N when 210N. I however was proposing that it might also be made to lock 215N (as pseudo point-to-point with 210) when 210R.
If however this is not implemented, there does need to be some locking that prevents one train being routed over 210R at the same time as another train is routed over 215R.
Think of it like this:
suppose the only points which 127B requires are 210R, 211R
suppose the only points which 128A requires are 215R, 211N, 212N
in this case (since 211 must be in one position or the other) than the two routes cannot both be set simultaneously. However a train using 128A would release 211 behind it once clears CN; would not want 127B to be able to set yet as CP would be foul of 210R, but 210 could have been reverse already in the scenario outlined above, so without effective locking provided by points some additional locking has to be provided. Note that whereas route locking is GENERALLY opposing locking it is not always; I hink it is this (and the headings sometimes used on the Control Tables) which may be causing confusion. Route locking can be in the SAME direction; e.g. for GK/RRT0044 locking, pre-set shunts etc

And another question: how do you jusitfy the length of TC, such as BE, BF. I can only find their total length is 450m, but can not know its own length, having difficulty in calculating the approach control time .

I agree there is not any certain clue but just make an estimate by proportion; AR looks to be a bit under 25% of the 450m so something around 100m.
Think why the IRJ would have been placed where it has been. a) 153 doesn't have a red so no definite need for a joint close to it, but sensible to have beyond the signal and relatively soon after it if practicable.
b) 144 has a PL of which viewing distance is 100m so looking at route box, notice that gives release as just AR occ. Hence we could assume that AR is no longer than 100m and could be comfortable that there would be no timer- this is simpler, saves money. Alternatively if feel that AR looks longer than 100m (and acknowledge that there is some advantage of the approach release not being very obviously associated with a track joint to avoid conditioning the driver to expect clearance), then could assume that it is say 125m and then show approach release time of say 5 seconds.
However, unless clearly in contradiction of signalling principles, I suggest just following the route box info; otherwise EXPLAIN why you are modifying. Don't worry about this small element too much; it really isn't going to make the difference between pass / fail of the exam- there are more important things to worry about