2008 - CT

[PJW]

Thank you for your detailed comments and encourgement.I have done this based on the knowledge gained from your comments previously posted in the forum.But still i want to gain more technics from you.

1.If treadle operated condition is proved for call on move, then time delay(approach control) not required is't correct?
2.Is it necessary to provide LWR for all shunt movement eventhough not specified in route table.
3.The note "Permissive working permitted in platform lines" not given in the layout, So I have assumed that "No permissive move".
4.How to mention overrun protection for the route 161A(M)?
5.For the route 161A(M) comprehensive approach locking:
FC,FD,(FE,FG OR 244 R),(FH OR 244R)--------149 ARAFOAL.
6.How to find the time delay for junction signal having MAR, ROL less than 55m-from the notes of yours re time values for IRSE exam purposes.
7.Explain the principle behind indirect opposing locking and how to find?
[124B(M)-135B(s) is indirectly opposing route]

-Sugavanam

I thought you must have had a good teacher !

1. I have never known a release to be after a time following treadle operation. Whereas a track joint being provided for othe purposes may not be in the right place, if a treadle is to be provided then it can be positioned precisely where needed. Treadles are expensive items requiring regular maintenance (it may be different as and when we get an electronic version approved for use), so tend only to use nowadays when there is no realistic alternative- hence use for approach release at all is now rare, tend to be used mainly for level crossings.


2. To UK NR standards, then yes LWR is provided for GPLs and generally for shunt moves associated with main aspects. Do so in the exam.


3. I now understand your logic and confusion. When it is said that permissive working either is or is not permitted in platform lines, what it actually means is whether the permissive operation of passenger trains is permitted (this is generally only nowadays permitted when two separate multiple unit trains are to join up so can proceed with onl;y one driver and inceasing capacity by only needing the one "train path"; however there are still some places where it is permitted that a second train can enter to use one portion of a platform whilst the other end has a separate train in it- primarly there are insufficient platforms and it is a way of using a long platform for two short trains without having to provide mid platform signals). However the ability to use a shunt signal to signal a locomotive onto coaches or to strengthen a mltiple unit train with extra unit from the sidings etc. is always regarded as permitted and yes, to be of use it would have to be permissive. It is the shorthand "permissive" which strictly should be "passenger permissive" that has created confusion; I am afraid that you just have to get used to what is really meant. Of course if you had experience of the operational use of such a layout then there wouldn't have been the confusion. At least the advantage of this website over a textbook is that you can ask such questions!

4. I'd write it in the Remarks column."Replaced by SPAD at 157 until BL clear, replaced by SPAD at 159 until CJ clear, replaced by SPAD at 164 until CF clear". Look for those signals from which a train could trail into the route (i.e. converge with it in either the same or the opposing direction), but omit any where the point calling of the CT's route would prevent- in this case 256N protects from a SPAD at 162. The track to specify is the one that is furthest from the protecting signal which is not already listed as being a track required clear within the CT's signal's aspect. Hence if doing the CT for route 156A(M) then wouldn't need to worry about SPAD at 154 or 152 as immediately the SPAD occurs CN or FE become occupied and these are proved clear anyway. Don't need to worry about SPAD at 124 as 236N is a requirement and thus there is flank point protection; however if the overlap had been EG onth then would have had to worry about "SPAD at 124 until EH clear" i.e once a SPAD has been detected at 124 then occupancy of DG, DH, DJ or EH would maintain 156 at danger.

5. Until signal ARAFOAL and tracks clear:
FC, FD, FE [(CP or 242N), FG or 244R] --------
FH --------or 149 ARAFOAL or 244R

Note the nested brackets - different types makes it more readible. The 244R condition applies to all within the [ ] whereas the 242N condition applies to those within the (), i.e. CP. If there had been more tracks beyond 149, then these would have been listed next to FG.

The first line of entry relates to the "first section in rear" and for 3 aspect signals there will be a second line of those rtracks conditioned out by a signal ARAFOAL. For 4 aspect sequence only, there would be a third line of entry and this would be conditioned out by either the first or second signals ARAFOAL.

Note that 149 can be cleared for a different route, then that route also needs to be conditrioned out by point lie (or alternatively you could state 149B ARAFOAL).

In reality it wouldn't be worth putting CP in the lookback at all since the approach in this direction is just from a GPL so no aspect sequence nvolved; I only included to show you what to do had this been a main signal.

6. Please rephrase the question as I don't completely follow what you are after. You certainly would never have a ROL less than 45m and nowadays less than 60m is unlikely (TPWS effectiveness even at very slow speed). The approach release for the shortest ROL is identical to that of a PL; i.e. train very nearly at a complete stand- the longer the ROL the earlier the release as a slightly higher speed approach is appropriate. Note that approach release for a Warning route is not referred to as MAR- this term reserved for approach release associated with junction signalling.

7. Yes you seem to understand it. For 124B(M) the direct opposing routes are 131B(S) and152A(M) and 164A(M/C) and 166A(S) - on the assumption that the overlap beyond 161 is only via 255R at the end of CH. These are directly opposing since they do not require any conflicting point positions. The indirect opposing routes are from the signals parallel to these; i.e. 135B(S), 156A(M), 162A(S). Whereas 135B(S) requires 237N and thus it INITIALLY does not oppose 124B(M) (i.e. it is the point locking which prevents the conflicting route from setting), once a train hascleared EG and is standing on EH, DJ, DH then the locking on 237 is released and thus they can be swung R. By this time the train from 135 is therefore indistinguishable from one that could have come from 131; therefore opposing locking is needed in just the same manner. To find opposing locking look for the "exit" of the routes in the opposite direction along the line as for the CT's route. Check EVERY signal that can read to that as a destination- regard them all as potential candidates for opposing locking, if you find one then look for all the "parallel" signals. Then remember to keep looking for routes that are further away but still overlap part of the CT's route and if you find one then look for all its "parallel signals"