2006 Part A Q2 POINTS

[alexgoei]

Appended please find my answers for the 2006 Exam Part A Q2.

I would appreciate it if I may have comments on my answers please.

Thank you

[YLP]

Appended please find my answers for the 2006 Exam Part A Q2.

I would appreciate it if I may have comments on my answers please.

Thank you

Dear Alex,

For Point 225, Signal 138 has not been incorporated.

I also have few questions to ask:
1. For Point 225 control table, the point lies in the overlap of 122A(M) only when 222 is in Reverse. In this case do we have to state this condition in the table also? say, "122A(M) or 222R"?

2. For Point 234, is the T.C. clear requirement on BS & ED absolutely required ? because I think
a. BS didn't foul the point 234
b. point 234 is already route locked by 142D

[alexgoei]

Hello YLP, Peter,

Thank you for your comments. I had another look at the answer and following review again I have decided to change the answers althogether which is now appended.

I will try to answer your questions to the best that I can. Like you I am sitting for the exams (not my first for Module 3 though) and my day job does not require me to work on control tables much less British practice. Do hope Peter can join in, clarify and comment on my answer especially the latest posted. The earlier submission of 9th July has not been answered but never mind it can be ignored.

With regards to your questions, you are correct that I have missed out routes from signal 138. So the entries are:

225 N > R Set by Routes/GF are 138 A(S), 138 B(S) with Sectional Route Locking Released by TCs Clear CN, CL, BN

225 R > N Set by Routes/GF are 138 C(S), 138 D(S) with Sectional Route Locking Released by TCs Clear CN, CL

and I have included them in my latest submission.

Looking again at 122A(M) with the exit signal at 134, Point 222 being a facing point is a swinging overlap. As long as the point is detected either in Normal or Reverse, the overlap for the 122A(M) can be in either lie - one AD, AE, the other BM, BN. However for the overlap on track circuit BN, 225 must be in a Normal position. It is reflected as a overlap locking timed to a stand on AC before exit signal 134.

With regards to Points 234, having looked at it again, I would make some changes to the entries for Requires TC Clear. Hence the entries should be:
Point Requires TC Clear
234 N>R CG, ED, CF, (BS or 233N)
234 R>N CG, (ED or 232N)

CG being the dead locking track circuit and BS a foul track circuit unless 233 is Normal. As for Point 233, it is for flank protection when Point 234 is Reverse. I have also assumed CF/BS and CF/CG are foul.
Assuming it is a six foot between the Up Main and the Down Main, I do not think there is sufficient clearance between. Based on previous comments on my other submissions to this forum, I understand the examiner will not penalise if assumptions are made unless they are way off.

So....

[PJW]

Do hope Peter can join in, clarify and comment on my answer especially the latest posted. The earlier submission of 9th July has not been answered but never mind it can be ignored.

Now back from a short holiday; too much in the inbox to deal with tonight as have only just got in and have things to do prior to early start tomorrow- I'll attempt to answer tomorrow night.

Firstly sorry I missed answering this one initially: you should have said! I suspect that I came back from away and another module 3 post had risen to the top of the list and this slipped beneath radar.....are there any others missed?

Re 234 deadlocking.
First I think you need to be careful in the direction of the locking. I actually prefer to put the "set by routes" as the first column so then the dead track locking is placed with all the other locking so this tends to reduce any N>R or R>N confusion. Particularly important when the straight route is R as in this case!

So I claim:
Locking N>R (i.e. preventing points being moved to straight lie):
CG, (BS or 233N),(EC or 235N) but both ED and CF are irrelevant

Locking R>N
CG, (CF or 233R)
I do wonder re ED as yes the very tip may well be foul of moves over 234N. However I don't want to lock 24 as the only overlap beyond 166 is via 234N and it is certain that the layout has been designed to have that overlap in use when another train is using the Down Branch (or else 235 would have been included within that O/L and indeed would have been numbered 234B instead). Therefore I'd be ensuring that 235 N>R would prove (ED or 232R) but not locking 234; remember that the main purpose of foul track locking is to prevent the signaller making an ill judged handsignalled movement on a path through the layout that seems to be free of trains yet something is overhanging the corridor through which the train is to pass. Only need to prevent one of the points getting into the lie for that movement, so I'd ensure that 235 protects and therefore 234 doesn't need to.

So re YLP's comment, for a handsignalled move along Down Main, the signaller needs only to key 234R and 232N; does not key points in overlap or flank, but only line-of-route. If the section of BS over 233R is occupied, there would be a collision; hence must prevent 234 going R, therefore BS is a conditional foul track for 234N>R.

Also why do you think that 234 should be route locked by 142D? I agree route locked by 142C as a shunt overlap is depicted beyond 166 and there isn't one along the Down Main but only towards the Branch- hence 234 must be set, locked and detected N. Indeed we'd want to be able to signal 138C up to 166 simulataneously with 142D up to 168; even if the very far ends of the two overlaps were foul of each other. Think about it; for a collision to occur requires 2 SPADs on PL moves to happen more or less simultaneously- liklihood extremely low, severity pretty small and the trains would hit anyway in a few more metres..... It is a bit unusual but there is a case at Labroke Grove outside London Paddington- introduced when we got some (shall we say exceptionally generous length) overlaps in the vicinity of SN109 after the accident.

Returning to other issues on 234 CT, I'd have expected 162C and 164B to call and lock 234N and 171 to soft call (i.e. call if free but not lock or detect) 234R as it would rather like to have flank yet the
layout suggests that ensuring that there can be no wrong direction move along the Down Main is the higher safety priority and thus it must yield.

Hope this has helped both of you re 234; 225 will have to wait until tomorrow evening I am afraid. Let me know whether the above has made sense or not......
PJW

[alexgoei]

Hello Peter,

Thank you for your comments.

Will go through them tonight.

Many thanks again for your unceasing efforts in helping me understand and prepare for the exams.

Regards

[PJW]

Hello YLP, Peter,

Looking again at 122A(M) with the exit signal at 134, Point 222 being a facing point is a swinging overlap. As long as the point is detected either in Normal or Reverse, the overlap for the 122A(M) can be in either lie - one AD, AE, the other BM, BN. However for the overlap on track circuit BN, 225 must be in a Normal position. It is reflected as a overlap locking timed to a stand on AC before exit signal 134.

I'll give more full comments later but overall the latest attempt for 225 was pretty damn good- there were just a few issues with the overlaps but considering the complexity you did well to get most.
Looking specifically at YLP's comment re the O/L of 122A(M) he is right. What you wrote above is also basically true (NB the "other overlap is AD, BM, BN) but is worded rather more re the aspect controls for 122 than the point locking- though of course for swinging overlaps these are indeed related.

So in the set by column you should have put:
[122A(M) w 222R]- with the "w" standing for "when" (reflecting it is only needs to be called sometimes, dependent upon the point lie of the facers)

Conversely the locking after 122A(M) which you have recorded only applies in the situation that 222 ar not free to swing away from directing the O/L onto the Up Main. Hence this should be written:
[122A(M) AD,BM,BJ,BK,AB, (AC ---- or AC -- for 30) ----- or 222N$28]
with the extra condition re 222N being written in the Remarks column linked by dashes and the square brackets holding the entire expression spread across 5 separate columns all together as clearly one item. You'd need to define the $28 (or just choose any # note if you don't want to remember the standard note) as "set or free to move"
You'll note that in the list of tracks I have also added the overlap track sections prior to the dead locking track BN as the overlap locking also needs to hold the points- they effectively have to be added at the front (out of logical running order) to ensure that they don't get muddled up with the time out condition re AC occupancy- if you really want to then you can write underneath the other tracks and link by a dashed line to be "after" the bracket; however this gets messy and takes up extra space so isn't often done.

You'll find there are other cases of such overlap conditions on some of the other routes; also what about 175A(M) and 122D(M)?
Conversely I don't think I'd make 122C(S) call N as there is an alternative overlap the other way; indeed it is a better one so I might even be tempted to make 122C(S) soft call 225R.....

Hope that addresses the issues that both Alex and YLP had; respond if need more assistance

[alexgoei]

Morning Peter,

Thank you got the reply. I will have to go through it this evening.

Regards