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Signal Placement
#1
I want to know how to place the signal in layouts after decided the signal aspect (ex :position of first signal)
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#2
(23-08-2011, 01:18 PM)ganeshg10 Wrote: I want to know how to place the signal in layouts after decided the signal aspect (ex :position of first signal)

Signalling The Layout for an MAS solution broadly comprises:
a) Analysing the implications of the braking characteristics and headway specification,
b) Determining the most suitable form of signalling to utilise on each portion of the route
c) Deciding on options for placing certain key signals to protect junctions etc
d) Considering all the operational moves etc which are required
e) Juggling the signal positions to best fit the various constraints
f) Specifying the signal profile and adding route boxes to define every route
g) Defining the lie of points, adding any traps needed, numbering etc
h) Dividing up the train detection sections appropriately, identifying, depicting overlaps etc
i) Adding explanatory notes where necessary, particularly re method of working, interfaces etc.

You actually asked where to put the first signal, presumably as a basis to define the positions of all the others in that direction, determined by the signal spacing calculated earlier. This is rather over-simplistic (although it is indeed on the correct lines); it is more of a matter at looking where the critical areas are, tentatively sketching an option for that area and seeing what implications it has for elsewhere; then seeing whether another option taking something else as a fixed point would give a better solution overall.

So there is no 100% clear answer:
1. If there is a major station with pointwork immediately beyond the platform ends, then platform starters are essential and basically give you some fixed places around which you must develop the remainder of your solution.
2. Sometimes though it is less obvious; if there is a junction area then need to consider whether to place the point work
a) within the overlap length of a protecting signal or
b) beyond that length;
indeed will the junction protecting signal be close to it at all.

Basically you are trying to balance
a) Safety - protecting junctions etc
b) Operational flexibility to operate the train service pattern required
c) Economy- provide enough but not excessive quantities of signalling.

I've tried my best to explain, at least from a UK mainline perspective, in the Study Pack on the DVD that all applicant for the exam should be sent. There is a lot of it to read because I have tried to explain thoroughly. The above is the outline, but if you want more detail then I suggest you need to wade through the DVD.



PJW
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#3
(23-08-2011, 01:18 PM)ganeshg10 Wrote: I want to know how to place the signal in layouts after decided the signal aspect (ex :position of first signal)

HI,
thank you very much for your valuable reply,
i have one more question.
Can you clarify me ,if i will do
calculation in UK-mainline practice
placing of singal -indian railways practice
is it acceptable one.
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#4
I think that this may be difficult; the first thing to ask is why not do all the paper to Indian Railway practice.

You must understand that I know very little about this (HELP SOMEONE?), but I have just a little knowledge (which is always a dangerous thing!......).

I am guessing but perhaps the practice you are familiar with is broadly to mechanical signalling principles, but with colour lights rather than semaphore signals and a few additional signals to break up long sections, but not what from the UK we would call true "Multiple Aspect Signalling".

If I am right then you would place your distant signals according to braking from the first stop signal and the capacity of the line would be determined by the length of the block section from one station / signalbox to the next, and the two factors do not interrelate in the same manner.

I guess therefore that you may be unable to answer this part of the question paper to the Indian practice with which you are familiar; a headway of 2 minutes may just not be possible on the system for which you wish to answer the question.

If this were the case, then provided you explain this briefly in your answer, I think that your proposal simply must be acceptable to the IRSE- after all it is hard to see what else you could do in the circumstances.

I'd welcome the views of others on the above

(24-08-2011, 08:19 AM)ganeshg10 Wrote:
(23-08-2011, 01:18 PM)ganeshg10 Wrote: I want to know how to place the signal in layouts after decided the signal aspect (ex :position of first signal)

HI,
thank you very much for your valuable reply,
i have one more question.
Can you clarify me ,if i will do
calculation in UK-mainline practice
placing of singal -indian railways practice
is it acceptable one.

PJW
Reply
#5
thanks for the reply,

can you give me simplified method(formulas) to find the aspect selection,headway & breaking distance calculation.
if you can give step by step answers,it will be good for me to understand.
Reply
#6
There are some step-by-step examples included in the Study Pack on the DVD.

Also there are some pretty good attempts on this forum, for example
this one which is certainly good for the non-stop headway. Then, if you follow the thread down, there is a detailed demonstration of stopping headway is included.

HOWEVER BEWARE.
It is not a question of finding a good example and memorising how to reproduce in the exam. The actual question asked does change subtly from one year's paper to another. Hence you do need to understand, so that you can interpret correctly.

You asked for simplified; I do not see how I can do this and still give enough detail. As an overview though for a TYPICAL question:

1/ Calculate using Newton's Laws of motion the distance to decelerate to a stand from the MAXIMUM PERMISSIBLE speed. This gives MINIMUM SPACING for 3 aspect signals.

2/ Take the required timetable headway time and assess whether there is a need to deduct a contingency allowance from it (based on level of traffic) in order to determine the signalling design headway. Suggest that a figure of 5% - 10% is often appropriate for the mainline layout.

3/ Convert the headway distance to headway time for a train travelling at uniform speed for which the non-stop headway is defined.

4/ Draw a diagram to show how this headway distance relates to signal spacing, overlap length, train length and sighting distance.

From here on it does very much depend on wording of the question.

5/ State assumption re extent of overbraking considered acceptable to address the risk that a driver may become accustomed to signals spaced widely and thus defers braking, then encountering a section which is tightly braked. A figure of 133% is often reasonable. From this work out what this constrains the MAXIMUM spacing of the signals to be.

6/ You now have a MIN/MAX range for signals based on safety braking considerations; also a MAX limit dictated by operability to achieve the required headway. Determine the more restrictive MAX constraint and then you have the permissible range of signal spacings.

7/ If there is an adequate range between MIN and MAX that in practice you ought to be able to place signals in places which
a) respect these values AND
b) fall in sensible places on the layout (i.e. correctly signal junctions and does not force signals in stupid places with respect to stations or standage needs)
then you have your 3 aspect solution which will work.
Note though if the headway need to not onerous (i.e. the period between trains is quite long), this would over-signal and therefore not be economical. In this case, decide on isolated 3 aspect signalling with the red/green signals spaced to suit headway requirement and each having its yellow/green signal on its approach separated by a distance based on the braking distance (I'd aim to place at approximately 105% but choose a nice round number easy to measure)

8/ If you find that the MIN is very close to the MAX then there is so little flexibility where signals can be placed that in reality it isn't practicable solution; see 9.

9/ If you find that the MIN is actually bigger than the MAX then clearly 3 aspects are not tenable. Therefore need to select 4 aspects because this gives two signal sections over which to brake.

10/ Might then need to determine a suitable spacing for the 4 aspects; to keep solution as economical as possible then these would need to be as widely spaced as they can be whilst satisfying their other constraints.

The question may sometimes require the student to determine what is the headway for signals placed at minimum spacing, sometimes to select an optimum spacing which economically just achieves the headway and satisfies the braking constraints, sometimes to determine the headway that would result from signals at their maximum spacing permitted by braking constraints etc.

Then there is the issue of the stopping headway calculations. Again the wording does change, so precisely what you do will need to vary accordingly.
I would often take the spacing determined as suitable for the non-stopping and use this to derive the consequential stopping headway; generally not asked to determine what the value actually is but only that
it achieves a specific value.
However do not try to run before you can walk; you need to be confident about the non-stop scenario first.




(24-08-2011, 01:39 PM)ganeshg10 Wrote: thanks for the reply,

can you give me simplified method(formulas) to find the aspect selection,headway & breaking distance calculation.
if you can give step by step answers,it will be good for me to understand.

PJW
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