IRSE Exam Forum

[attachment=49][attachment=50]I have attempted the 2007 Module 3 Paper for the Control Tables & Aspect Sequence.

Are there any comments please on the answers.

Thank you

233 points
These are switch diamonds which have been separately numbered (as per latest NR practice but also see below) from the associated single end 231. Alex hasn't stated the practice he followed but a reasonable assumption from this CT is current Network Rail with SSI.

Dead track locking:
It is obviously correct that CJ locks both ways. It is also correct that 233 should be prevented from normalisation if the closest portion of BJ were occupied since this is FOUL; therefore the (BJ or 229N, 231N) is correct.
However I would not have put the (CK or 232N) entry; if there is a train leaving the Up Branch this would prevent the signaller from setting for example 129B(M) had 233 been left reverse after a previous movement to the Down Branch. Foul dead track locking is primarily provided to stop the signaller from moving points induividually into a position which defines a route over which they might authorise a handsignalled movement that APPEARS to be OK (all tracks in line of route clear) yet when there might be a train so close to that route that there is insufficient clearance. In this case normalising 233 gets them to point AT the occupied track CK and indeed 232 are being locked the wrong way for a move from 144 (for example).
Now considering the N to R locking. I don't think it is strictly necessary to prove BJ clear; however to do so is not restrictive. Hence it is probably a good idea to do what Alex has done and include it; after all it would have had to lock the points had 231 been numbered as another end of 233 (obviously such a numbering scheme would only have been appropriate on a simpler track layout without the slip connection 229). The locking that has got MISSED is what should be preventing 233 from being reversed if there is a train on the Up Main which has just passed over them in the normal lie but has travelled an insufficient distance to be clear i.e. there should be an entry (CK or 232R) in the top cell of the second column of the CT.

Set By:
I agree with the entries in the lower cell of the third column for those routes that call 233 normal. Alex has obviously followed recent practice by giving shunt routes overlaps since 123A(S) is included [the REAL one not the examiners' mistake!]. There is a hint that this is the practice tacitly assumed by the layout (but remember candidates can CHOOSE their practice) as the SE/SF joint is drawn as an overlap and labelled "shunt 60m". There is no need (and better not to) annotate 146A(S) with a note "requires 124 set"- this is not relevant to the points CT. Indeed the route box requirement is actually "requires 124 off" (i.e. aspect cleared and therefore approach locked, rather than just route having been selected)- subtly different.
Conversely I don't agree all the routes calling the points Reverse; 123C(S), 136A(M), 182B(M). I can see why the routes over 232R would be "happier" to have 233 set for a parallel move, but as explained above re the dead track locking, the Down Main moves "want" 233N when 231N. Assuming that we need to be able to run a train on the Down Main simultaneously with one from the Up Branch (of course!), then "something has to give". Hence the Down Main "wins" and the aspects of routes along the Up Branch must be content to prove CJ clear [#1]. Note that a train from 123B(S) would continue to lock 232N whilst on CJ and thus routes such as 136A(M) would only be able to set once CJ clear.
[#1 The condition on CJ to prevent aspect replacement for a parallel move should be expressed as a track sequence- the position of switch diamonds can't be relied upon to give flank protection and if an invalid movement is made the prove may either carry on diagonally or more likely derail].

Routes 138B(M/C) were overlooked!

Route holding
Column 4 should be amended as per column 3 comments.
The associated columns 5-7 are generally Ok and bracketing the routes together that have the same tracks is a useful exam technique to save valuable seconds.
Track BF is missed from 123A(S)- easy done when the track name is on a portion of the section which is not traversed BUT you need to train yourself not to make such errors- be conscious of the IBJs and go look for the name in each case! Also te track names have simply been put in one list; there is an overlap portion that should time out in the same way as it does for 113A(M)(W). Actually there is no need for the route locking to include the overap tracks BJ, CJ as these are dead locking tracks; whereas tracks within the ROUTE have 15 second anti-track-bob protection and thus the route locking over dea tracks should be shown, there is no such additional locking once the overlap is entered- doesn't do any harm but adds nothing so shouldn't record. BK is certainly wrong- don't just put all the overlap tracks down without thinking; train is beyond the points by the time only BK occupied.
For the locking in the opposite direction, somewhat similar comments re 182C(M). In this case we DO need to list EA as ths is part of the overlap PRIOR to the commencement of the deadlocking of the points. This overlap shoul also time out on EB for a suitable time but the brackets should be arranged that EA is outside the bracketted condition so that the locking is held indefinitely if this becomes occupied following a SPAD.

Overall, not too bad- the switch diamonds made the foul TC locking a bit tricky and you got much of it.
A useful tip is to compare the tracks listed in each of the maintained locking entries (col 5) with those included in the dead locking (col 2)- route locking should go up to AND INCLUDE, overlap locking should go up to BUT EXCLUDE. If there is a foul track and the relevant route passes over it, then yes INCLUDE that track within the list of route locking tracks. Conversely don't put tracks in this list that are after the relevant train has passed beyond the dead locking tracks.
Remember that the locking on points is imposed when they are first called by a route (col 3) and then held until that signal is free of approach locking (col 4). They also need to be held by a train that has passed beyond that signal but has yet to pass safely beyond the points (i.e. to be totally clear of them- this means not on a foul track)

[BEWARE those familar with RRI rather than SSI.
RRI would correctly have slightly different route locking entries etc. since it is usual practice for there to be no anti-track-bob protection and thus route locking would not generally show any tracks which dead lock]

Need also to get a bit more familiarity re overlap locking; certainly don't forget to make them time out!

Comments on the other CTs will have to wait until later occasion!

235 Points
The thing about these points is that they give passenger lines trapping protection from the run round siding.

1. NR would give these a "restoration alarm" to remind the signaller that they had been left reverse or even "autonormalise"- this should be noted in the Remarks column.

2. All routes over 236N should be calling 235 normal as flank, but in addition to this routes over 239N should also be calling 235 normal to ensure that passenger line gets trapping protection. Note that this applies even if 235 are made to be auto-normalising (there is always a chance that signaller leaves keyed reverse etc). Alex has done this and indeed for good measure has decided also to call trap for those moves into Down Yard. This is a good idea but I think that I'd make these routes a "soft call" such that they would take the points if free, but could still set if they weren't. I certainly (and this would show not here but on the route & aspect CT for the relevant routes) would NOT detect 235 so that the PLs could clear even if detection was not achieved for some reason.

3. When points are called as trapping, then trains on those routes may never reach the "deadlocking" tracks so the usual rule (recorded i/c/w 233 above) needs slight modification. Trapping needs to be maintained until a train on the route has passed beyond the place where a collision with errant vehicle would be possible. hence for routes such as 146D(S) then the route locking tracks would be BL, BK, SG.

4. Certainly for routes such as 146B(S), the route locking tracks should be BL, BK, SF, SE. SE is certainly FOUL (as can be seen by the placement of the CP arrow and indeed the general rule that joint is close to the convergence than the switch tongues on the parallel line presumably at 6ft spacing). This is where comparison with the deadlocking track column would avoid such an error, since SE is correctly included in it.

5. Whilst looking at column 2, there is an error here. SF track is the track over the points and thus should ALWAYS lock them; the "or 236N" condition on the N to R locking is incorrect.

6. Now returning to columns 5-7 to look at the locking of the points when in overlap.
Alex has followed Signalling Plan and provided locking after 109B(S) and has correctly shown it timing out. Mention of SE is superfluous as this is an overlap track that deadlocks anyway.
However the entry for 113A(M) is right to include the overlap tracks as well as those in line of route; because 235 are trapping points not adjacet to the route then BJ, BK are not deadlocking and thus must be in the maintained locking. Note the listing of the tracks has to be out of sequence so that occupation of BH for a time does not override the locking on these tracks as well- the bracket excludes.
However 113A(W) should NOT lock the points as the ROL is situated at the BJ/BK joint. It would appear that the principal reason for providing the ROl on this layout is to permit a passenger train to be drought into Down platform simultaneously with a movement into / out of the Yard via 239R and if 235 are locked N then moves from that particularsiding could not be made (and of course 238A serves a similar role in providing trapping and thus would be given the equivalent locking). Even if there was a SPAD at 129, the train would not be endangered until it had passed beyond the ROL that had been reserved for it, so trapping is not required.
One route that might have been worth considering is 109A(S) that could have called and locked 235N, except when a forward route set from 133. In this particular case I don't think worth the complexity and Alex's approach of making routes over 238R call 235N (pseudo point-to-point) is probably the better. However on a different layout having traps at the end of a Goods Loop off a mainline, this would be more appropriate; if your practice (NR's current practice) is to give overlaps even for freight moves on Goods Lines then you'd need to consider whether there is a sufficient overlap into a spur with the trapping points normal, you may need to call reverse and direct the overlap back out onto the mainline until the train is safely stopped and then the trap points can be normalised.

7.The 158A(S) entry is wrong. The clearance of 158 purely relates to the move as far as 146- there is no overlap shown. The route box specifies that it requires 146 off; i.e. a driver will not (except in unusual failure conditions) encounter 146 at danger. It is practice in such situations to allow the signaller to be able to set the routes in either order but the order of aspect clearance is first 146, then 158. The approach locking lookback of 146 is designed to be taken back to 158; there is no need therefore for a concept of am overlap beyond 146 since the route is being held via the locking of 146 itself. 146 has some routes that call 235N and others that call 135R so it should be obvious that 158 must not lock them (as it wouldn't know which way!). So when doing point CTs if you see that a route demands as a pre-requisite another signal off, this is probably a hint that it ISN'T necessary to include it on the CT, because the other one has already imposed any requisite locking. If the stated requirement is just that it needs another route set, then similarly there is no poiint calling to worry about, but you do need to consider how the locking is being maintained.

Overall Alex would get good marks for this CT as has clearly demonstrated that understood the significance of the trapping protection being afforded by 235- probably a contrast with many candidates whose CTs would have been somewhat lacking in entries as they thought it was an easy point!

Thanks Peter for the very detailed explanation.

Yes the CT is based on current Network Rail.

I will go through your explanation and if I need further clarification can I get back to you please.

Thank you once again and look forward to you other comments

[attachment=56]

alexgoei Wrote:I will go through your explanation and if I need further clarification can I get back to you please?
Thank you once again and I look forward to your other comments

Indeed please do- or any one else for that matter.

Aspect Sequence
This is good- clear, neat and accurate. Sorry to detract, but I must say that I think it was a pretty easy one compared to most years. The Down direction wold have had the ROL (comes up most years) and the flashing aspect and therefore a bit more meat.
Not much to say about what you did:
a) Having adopted the diagonal lines for the "Green up to Double Yellow or Green", you probably should have done the same for all places where the sequence lines join; this reserves the angular vetical line for the "approach release step" which just makes it all clearer. I am a bit of dinosaur and regret the fact that most charts today go for the pure vertical / pure horizontal presentation for everything just because it is easier for the CAD operator without thought of the usefulness for the end user.

b) Your "end of TC area" beyond 116 is sensible (as strictly speaking no overlap symbol was utilised); the situation beyond 142 is similar but is less clear-cut as arguably there is an overlap back out onto the running line so I'd have been tempted just to denote it O/L and leave it like that.

c) Just a word about the POL beyond 182- the extent of the train detection in the section signal in rear- let's call it 186- would include ED track, as shown by the overlap symbols. The significance of the POL is that it signifies that a train can be signalled up to 182 simultaneously with one up to 173/5. Although there is only one element of train detection between the opposing signals (ED) the OVERLAP is not being shared as each signal has its own distinct required length to the place annotated POL and so no sharing is involved; it is just that this place is not obvious on the ground (being a theoretical concept rather than the site of a train detection boundary). However for an aspect sequence diagram the POL can be ignored- it is the whole of ED being proved clear within the controls of the rear signal. I know of candidates who decided against doing this particularly asy question purely because they were worried what to do about the POL (answer = NOTHING!)

d) The approach release time on CD for 162 approach release is very high. OK we don't know the length of the track and the sighting distance of PLJI versus main aspect but that time value feels like a "time completely to a stand" value. We only need to ensure that driver has passed signal in rear (CD itself proves that) and also that there is no risk of seing the main aspect clear to Yellow without also seeing PLJI; it is possible that it may not need any time but the safest thing for IRSE exam is put a time value such as 15 seconds to delay a bit but not a lot.

e) The question what to show on the sequence chart beyond 138 is "interesting". There is no overlap as such shown on the plan. I'd be reasonably comfortable with this IF 182 demanded 138 off; however it only demands "set". I think we need to decide [SO STATE TO EXAMINERS AS ASSUMPTION] that "set" means not just routed but also "signal not disengaged" and also "approach locking not in process of timing out"- i.e. that we know that the train for which it is set is indeed the one which is approaching it. Even that doesn't totally resolve the issue for 138A(M) as potentially we could two following trainson the same route and once the first is on CJ then 138 could be cancelled and overset for the next train waiting at 182. The only thing that would then be holding the aspect is the first train occupying tracks in the aspect overlap; there will be a place at which it passes beyond those tracks proved in 182 but exactly where this is has to be a guess since it is not depicted. Hence I consider the plan deficient but the exam is probably not the place to be too strident and it has all got rather convoluted for the aspect sequence chart. Hence I think I'd just mark as O/L in the usual manner but add a note "NB. extent of aspect overlap relevant for following train is not depicted on plan but I guess extends to include BJ". This makes it clear: 1) you have studied and understood plan, 2) you can make reasonable assumption, 3) you think plan is wrong but too polite to say so.

Route and Aspect

Blank CT
A good demonstration of the advantages and disadvantages of the column approach. There is not a lot of space to play with and need to consider widths both for content of the cells and the wording for the titles. Very difficult to get best compromise but this is reasonable, though note how some are full whilst others light- however a route having many points R rather than N is always a possibility to be considered. A significant Approach Locking lookback would have been impossible to depict in the column allowed; similarly the swinging overlap would also have been difficult (you missed it!).
I suppose from exam technique viewpoint: for a pass it is most important to rattle through quickly all the basic locking (and ignore any complexity as not worth the time), then this CT does the job but if you adopt be aware of its limitations- personally I would give up the separate sub columns within the points (use suffixes) and also try to save valuable width used for Approach Locking release, perhaps by writing column heading sideways. What you can't get away from with this style of CT is how to specify what controls are in the route level and which in the aspect- so for "real life" I don't like it and personally would have so much difficulty trying to use it that I'd prefer a more 11202 style. However I think you have made the right choice for you so stick with it,b but possibly refine slightly with experience of use.

The heading of the route locking columns is a bit of a mix and match hotchpotch. I suggest for the lower row:
[TC clear] or ([TC occ] [for time]) [after signal operated]
The top two rows should be combined and read
EITHER OPTION 1: Route and Route Locking Normal
OR OPTION 2: Signal At Red And Free Of Approach Locking and locking maintained until
Given exam constraints I think option 1 has advantages!

The one thing I urge is LEAVE SIGNIFICANT SPACE UNDER LAST ENTRY before ruling a line and starting the next route- otherwise when you later discover that you have missed something howon earth are you going to be able to add it?

General
1. Replaced by. You have just entered the "stick" track in each case. Nothing wrong with that per se but the NR standard for about the last 25 years is the use two tracks simulataneously occupied to disengage the signal stick- "berth" and "stick". Would be particularly important if there was TORR. If you are claiming "modern NR standard" then I think you should adopt.

2. Oposing route locking. Generally OK but not completely secure- you have missed some "indirectly opposing" yet have put route locking that is not actually required since it is locking a set of points in the last track prior to the relevant signal- the point availability is sufficient to prevent to route from setting. Similarly the extent of the route locking and the "timing off" isn't always right and is certainly often incompatible with the tracks being proved clear in the aspect of call-on or shunt signals. Sometimes the locking of an opposing move has been taken onto the berth track of the signal for which doing the CT- the locking would be preventing a train being routed as it would consider itself to be an opposing movement!

There are various other detail issues and I am thinking how best to feedback; I have just remembered another of my dislikes of this style of CT- no spare space anywhere to right in omissions or corrections!

So that'll have to wait until another evening, but provided you crack the route locking most of the rest of the basics are ok. I am impressed that you saw the need for routes to get themselves trapping from 238 as well as 235 (though you needn't have worried re 236- but apart from minor reliability impact that does no harm).

NOW ADDED ATTACHMENT FOR 113AM

regards,
PJW

Peter

Thank you for the comments.

Will go through them and hope to submit the answers to the 2006 paper by Friday 4th July.

Alex

alexgoei Wrote:Peter
Thank you for the comments.
Will go through them and hope to submit the answers to the 2006 paper by Friday 4th July.
Alex

It took me a bit of time to finish off notes re 2007 which are attached to this post; I'll then get around to the 2006 as soon as I can fit it in. Don't let me stop anyone else from giving their comments though!

PJW

I have some confusion about your explanation?
1. 113A(M/W),123A(S) all lead to 129, and the joint between EA/EB shows a small "129". So can I take EA as the overlap of 129? and think train must run into BJ&EA after passing 129 in the route of 113A(M/W),123A(S) ?

2. Why ignore 136A,123C(S) and 182B(M) when considering 233R? Sorry, I can not understand your explanation very well... Is it because 233 is crossing point? And crossing point has priority when setting routes?

3. Referring to 182C(M), does it have overlap? And which TC is its overlap? I can not find in the layout... SA??

4. Why they consider 144A(M), 142A(M), 136A(M), but ignore 144A©,142A©,136A©? They all do not have control box, but I suppose 142 136 and 144 all have call-on routes. Am I right?

Referring to point 235?
I think 236R calls 235N, but not 236N calls 235N...

And why 238 and 235 is point to point? I suppose 238R doesnot need 235N.... could you kindly give some hints about this reason? I have read your Study Note, but I do not think it can be classified to those 3 types of point to point interlocking...

(28-06-2008, 08:10 PM)PJW Wrote: [ -> ]233 points
These are switch diamonds which have been separately numbered (as per latest NR practice but also see below) from the associated single end 231. Alex hasn't stated the practice he followed but a reasonable assumption from this CT is current Network Rail with SSI.

Dead track locking:
It is obviously correct that CJ locks both ways. It is also correct that 233 should be prevented from normalisation if the closest portion of BJ were occupied since this is FOUL; therefore the (BJ or 229N, 231N) is correct.
However I would not have put the (CK or 232N) entry; if there is a train leaving the Up Branch this would prevent the signaller from setting for example 129B(M) had 233 been left reverse after a previous movement to the Down Branch. Foul dead track locking is primarily provided to stop the signaller from moving points induividually into a position which defines a route over which they might authorise a handsignalled movement that APPEARS to be OK (all tracks in line of route clear) yet when there might be a train so close to that route that there is insufficient clearance. In this case normalising 233 gets them to point AT the occupied track CK and indeed 232 are being locked the wrong way for a move from 144 (for example).
Now considering the N to R locking. I don't think it is strictly necessary to prove BJ clear; however to do so is not restrictive. Hence it is probably a good idea to do what Alex has done and include it; after all it would have had to lock the points had 231 been numbered as another end of 233 (obviously such a numbering scheme would only have been appropriate on a simpler track layout without the slip connection 229). The locking that has got MISSED is what should be preventing 233 from being reversed if there is a train on the Up Main which has just passed over them in the normal lie but has travelled an insufficient distance to be clear i.e. there should be an entry (CK or 232R) in the top cell of the second column of the CT.

Set By:
I agree with the entries in the lower cell of the third column for those routes that call 233 normal. Alex has obviously followed recent practice by giving shunt routes overlaps since 123A(S) is included [the REAL one not the examiners' mistake!]. There is a hint that this is the practice tacitly assumed by the layout (but remember candidates can CHOOSE their practice) as the SE/SF joint is drawn as an overlap and labelled "shunt 60m". There is no need (and better not to) annotate 146A(S) with a note "requires 124 set"- this is not relevant to the points CT. Indeed the route box requirement is actually "requires 124 off" (i.e. aspect cleared and therefore approach locked, rather than just route having been selected)- subtly different.
Conversely I don't agree all the routes calling the points Reverse; 123C(S), 136A(M), 182B(M). I can see why the routes over 232R would be "happier" to have 233 set for a parallel move, but as explained above re the dead track locking, the Down Main moves "want" 233N when 231N. Assuming that we need to be able to run a train on the Down Main simultaneously with one from the Up Branch (of course!), then "something has to give". Hence the Down Main "wins" and the aspects of routes along the Up Branch must be content to prove CJ clear [#1]. Note that a train from 123B(S) would continue to lock 232N whilst on CJ and thus routes such as 136A(M) would only be able to set once CJ clear.
[#1 The condition on CJ to prevent aspect replacement for a parallel move should be expressed as a track sequence- the position of switch diamonds can't be relied upon to give flank protection and if an invalid movement is made the prove may either carry on diagonally or more likely derail].

Routes 138B(M/C) were overlooked!

Route holding
Column 4 should be amended as per column 3 comments.
The associated columns 5-7 are generally Ok and bracketing the routes together that have the same tracks is a useful exam technique to save valuable seconds.
Track BF is missed from 123A(S)- easy done when the track name is on a portion of the section which is not traversed BUT you need to train yourself not to make such errors- be conscious of the IBJs and go look for the name in each case! Also te track names have simply been put in one list; there is an overlap portion that should time out in the same way as it does for 113A(M)(W). Actually there is no need for the route locking to include the overap tracks BJ, CJ as these are dead locking tracks; whereas tracks within the ROUTE have 15 second anti-track-bob protection and thus the route locking over dea tracks should be shown, there is no such additional locking once the overlap is entered- doesn't do any harm but adds nothing so shouldn't record. BK is certainly wrong- don't just put all the overlap tracks down without thinking; train is beyond the points by the time only BK occupied.
For the locking in the opposite direction, somewhat similar comments re 182C(M). In this case we DO need to list EA as ths is part of the overlap PRIOR to the commencement of the deadlocking of the points. This overlap shoul also time out on EB for a suitable time but the brackets should be arranged that EA is outside the bracketted condition so that the locking is held indefinitely if this becomes occupied following a SPAD.

Overall, not too bad- the switch diamonds made the foul TC locking a bit tricky and you got much of it.
A useful tip is to compare the tracks listed in each of the maintained locking entries (col 5) with those included in the dead locking (col 2)- route locking should go up to AND INCLUDE, overlap locking should go up to BUT EXCLUDE. If there is a foul track and the relevant route passes over it, then yes INCLUDE that track within the list of route locking tracks. Conversely don't put tracks in this list that are after the relevant train has passed beyond the dead locking tracks.
Remember that the locking on points is imposed when they are first called by a route (col 3) and then held until that signal is free of approach locking (col 4). They also need to be held by a train that has passed beyond that signal but has yet to pass safely beyond the points (i.e. to be totally clear of them- this means not on a foul track)

[BEWARE those familar with RRI rather than SSI.
RRI would correctly have slightly different route locking entries etc. since it is usual practice for there to be no anti-track-bob protection and thus route locking would not generally show any tracks which dead lock]

Need also to get a bit more familiarity re overlap locking; certainly don't forget to make them time out!

Comments on the other CTs will have to wait until later occasion!

---

(12-06-2010, 12:57 PM)greensky52 Wrote: [ -> ]I have some confusion about your explanation?
1. 113A(M/W),123A(S) all lead to 129, and the joint between EA/EB shows a small "129". So can I take EA as the overlap of 129? and think train must run into BJ&EA after passing 129 in the route of 113A(M/W),123A(S) ?

I would normally interpret the numbers adjacent to overlaps to be their length in metres, but certainly in complex areas it is a convention that the relevant signal numbers are noted next to the overlap, though I would suffix G. In this case it does seem that it does mean this as there is the suffix OL and it would otherwise be a strnge coincidence of signal numbering and the fact that overlap lengths normally are quoted to +/- 5m. I think that it is trying to tell us that it isan overlap beyond 129 but not 127, athough it isn't completely clear. So I agree with your interpretation' let us state our assumption and carry on on that basis. However it makes no sense that this is the ONLY overlap; BK/BL would be an overlap beyod 129 and (at a different time of course) beyond 127 as well. Hence I DISAGREE that the train if passing 129 would definitely run onto BJ then CJ (you missed that one!) and then EA; although I agree that this would be the case IF 231 Reverse.

Quote:2. Why ignore 136A,123C(S) and 182B(M) when considering 233R? Sorry, I can not understand your explanation very well... Is it because 233 is crossing point? And crossing point has priority when setting routes?

Several issues:
A. 233 are switch diamonds; they don't give the same value re diverting trains as flanks as a normal point end would do. If we put 233R and then there was a SPAD at 144 the train would trail 233B and almost certainly derail at 233A since it encounters an abrupt change of direction rather than a curve.

B.Even assuming that it did gve some useful trapping, we would then have a choice between
a) calling 233N by routes over 231N (and not calling 233R by routes over 232R),
b) calling 233R by routes over 232R (and not calling 233N by routes over 231N),
b) calling 233R by routes over 232R and calling 233N by routes over 231N but this would mean that we could not route a train from Down Platform to Down Main simultaneously with another train from Up Branch to Up platform- no real reason for this and would be operationally restrictive.

C. Of course if the junction had been sharper and slower speed then there would be no 233 but just a fixed crossing and we couldn't do anything ith that re flank could we?

D. An alternative manner of arranging the numbering of the junction would be to use "3 ended point numbering"; 231 becoming 231A, 233A becoming 231B and 233B becoming 233C.

E. There is sense in setting and locking points that don't actually give useful flank as it tends to lower the chance of a mistake being made in degraded working when signaller has to move points and authorise trains past signal held to danger. For 144, 231 does provide useful flank; for 129A/B by making the signaller set 233N it at least locks out routes such as 127C.

Hence all my instincts are to go for option a) in the list above.

Quote:3. Referring to 182C(M), does it have overlap? And which TC is its overlap? I can not find in the layout... SA??

Yes and No!
It doesn't have a "locking overlap"; there is a note on the plan near 138 wich says it is only approachable when there is a forward route set from the signal and it is this route that defines the point lie. This is a safety feature; although 138 could be at red and thus suffer a SPAD, there would be no "junction collision" but only a lower risk rear end collision at worst.
There will obviously be an "aspect overlap" as a choice has to be made re the limit of track cirrcuit controls to include. This has not been defined so you state your assumption and implement. I'd say EA, CJ but possibly also BJ.

Quote:4. Why they consider 144A(M), 142A(M), 136A(M), but ignore 144A©,142A©,136A©? They all do not have control box, but I suppose 142 136 and 144 all have call-on routes. Am I right?

Thee signal profiles do not have a PL symbol; therefore they cannot have call-on routes.

Quote:Referring to point 235?
I think 236R calls 235N, but not 236N calls 235N...

And why 238 and 235 is point to point? I suppose 238R does not need 235N.... could you kindly give some hints about this reason? I have read your Study Note, but I do not think it can be classified to those 3 types of point to point interlocking...

235/236 at first glance seems to be a crossover but by numbering separately as they have you can see that it is possible for the N lie of 236 to direct a train towards the siding (away from the station) whilst still maintaining the trapping from that siding and thus getting the best of both worlds.
You would not want 235 to go from N to R unless 236 already N and if implementing directly via point-to-point locking then 236N detection would be proved before permitting 235 to be moved either by the Individual Point Switch or route setting.
If only implementing at route setting level, then you'd say that all routes calling 235R would also call 236N but that is plain common sense for line of route anyway, so scarcely worth a mention.
With point-to-point, having got 235R then 236 would be locked N; for 236 to go from N to R would need 235 detected N.
Implementing this at route level leads to all routes over 236R need to call 235N (the signalling reason for this is that as they would want trapping from the siding).

To me, the point that is most likely to be given point-to-point with 238 is 239 for similar reasons (and a bit of a hint is that the two points are within the same track circuit).
However there is indeed also an argument for 235 & 238, since one could never actually need these points both to be reverse simultaneously for any one, or any combination of, train movements. Hence by preventing points ever getting into that state cuts down the "degrees of freedom" and simplifies things in the context of mechanical interlocking- it makes sense to put as much point-to-point in as possible as it cuts down the need to provide other locking quite considerably.The arguments for point-to-point when implemented on route relay interlockings are far less strong.

However the useful thing about being able to spot it is that it tends to prompt you to think about flank protection and trapping that can so easily get overlooked when doing Control Tables against time constraints.

Thank you. All your state is very useful for me.
I think I indeed need to add some more knowledge on flank protection and trapping which I almost know little...