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2007 Mainline layout
#1
Seems like a fairly straight forward layout.. however, the spec asks for standage for a freight train clear of the junction and single line at C on the down valley branch, in both directions. Freight train is 400m long, the branch isnt quite. How is standage possible without fouling either the junction or the single line. Am i missing something obvious? (is it just a really tight fit?) Any help or a hint would be much appreciated. Thanks
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#2
Astubbs Wrote:Seems like a fairly straight forward layout.. however, the spec asks for standage for a freight train clear of the junction and single line at C on the down valley branch, in both directions. Freight train is 400m long, the branch isnt quite. How is standage possible without fouling either the junction or the single line. Am i missing something obvious? (is it just a really tight fit?) Any help or a hint would be much appreciated. Thanks

I'm not in the same place as my copies of the layouts and I cannot remember it in enough detail. Can you scan a section to remind me? Otherwise, I'll have a look in the office, but that might not be until Wednesday. Unless anyone else has one to hand.
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#3
Peter Wrote:
Astubbs Wrote:Seems like a fairly straight forward layout.. however, the spec asks for standage for a freight train clear of the junction and single line at C on the down valley branch, in both directions. Freight train is 400m long, the branch isnt quite. How is standage possible without fouling either the junction or the single line. Am i missing something obvious? (is it just a really tight fit?) Any help or a hint would be much appreciated. Thanks

I'm not in the same place as my copies of the layouts and I cannot remember it in enough detail. Can you scan a section to remind me? Otherwise, I'll have a look in the office, but that might not be until Wednesday. Unless anyone else has one to hand.

Andy,

I haven't actually done the layut myself nor checked anyone else's attempt and only have a reduced size photocopy available here. However I think the answer is that it is a "VERY tight fit". You could put signals at the 1400m datum, basically at the clearance point for the convergence to a single line over the viaduct. You could argue that that would place the rear of the train at the 1800m datum, which certainly on the Down Branch would be foul of the switch diamonds. If you decided "to measure around the curve" then I reckon that you might just get opposite something like 1790 on the datum scale and thus just be clear- I think that is what examiners intend. [Opposite direction basically similar- the signals will obviously be some 5m "inside" the relevant IRJ positions]

However I would take issue with them- the need to add in a defensive driving allowance for a driver aiming to stop 20m back from exit signal, leaving a margin for error in stopping, say 5m, and still wanting the rear axle of train suffiently beyond the clearance block joint so that slight backwards movement (rebound from buffers when stopping or indeed slight roll-back when starting) would not drop adjacent track and revert aspects for the mainline. Hence I agree with you that you cannot provide the standage requested; you have understood perfectly.

The question is, as a candidate what can you do? Examiners will probably not welcome you claiming that they are wrong so I wouldn't advise that (I have the luxury of picking my time to argue with them in private; you obviously don't). Hence I would treat is as you may have to do in real life; as a client requirement that cannot be met. You do provide the maximum standage that you can- let's say that you think you can get a maximum of 390m between a signal and the IRJ at the further end of the loop and that with the various allowances believe that it only gives practicable standage for 360m train. Mark it up as such with a note that says: "Unable to achieve specified standage; client has choice between reducing aspiration or relocating branch points 40m towards viaduct. This is likely to be determined by what percentage of freights are really the full maximum length, the cost of relocating the points and the whole-life implications of positioning these very close to the viaduct and the operational impact of insufficient standage".

Moral: don't spend time agonising- have the confidence to know you are right, go with it and spend a few seconds explaining. You can't be expected to be a magician; you get the marks for being aware of the requirement, doing the best you can and flagging up the non-compliance and suggesting some possible options. Indeed clearly demonstrating awareness of a layout needing to compromise between the competing SAFETY / FLEXIBLE OPERATIONS / LOWEST COST imperatives is a definite bonus- you use the situation to your advantage to demonstrate your experience and "railway common sense". Complete the rest of the layout satisfactorily and it could be that very note which tips you over the edge to get a Credit, do the rest of the layout well and it could be the thing that gets you a Distinction.
Hence see it as an Opportunity- perhaps the examiners are cannier than we give them credit for; perhaps they engineered it that way on purpose to see who would rise to the occasion. Remember the exam has two roles; firstly set a standard to which we'd expect all signal engineers to reach and secondly pick out the very best of the bunch.
PJW
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#4
Thanks Peter.
I appreciate your response, some interesting things to think about.

Andrew
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#5
Hi

Could someone please give me a clue as to how I could signal the layout across the single line section over the viaduct. If I was to have a protecting signal at 1300m, prior to the DOWN VALLEY/UP VALLEY junction a train could potentially be standing partially over the viaduct, is this allowed?

Alternatively could the signal protecting this junction be moved back to the DOWN VALLY BRANCH prior to the single line section.

Apologise in advance if I'm asking a noddy question but in my defence I am a novice!

Thanks - Paul
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#6
probert1 Wrote:Hi

Could someone please give me a clue as to how I could signal the layout across the single line section over the viaduct. If I was to have a protecting signal at 1300m, prior to the DOWN VALLEY/UP VALLEY junction a train could potentially be standing partially over the viaduct, is this allowed?

Alternatively could the signal protecting this junction be moved back to the DOWN VALLY BRANCH prior to the single line section.

Apologise in advance if I'm asking a noddy question but in my defence I am a novice!

Thanks - Paul

1. As so often is said- you must signal to your railway's practices; without knowing which environment you are familiar with it is not possible to answer clearly.

2. Signalling rules are not like the 10 Commandments in the form of "Thou shalt not....." given from on high. You need to think of them more as "accumulated wisdom" of best practice / avoidance of things which have proved unsatisfactory in the past - that is why accident history (not just of the spectacular crashes) is important.

3. Where "rules" exist you need to understand the WHY the rule exists as much as WHAT the rule is. This is because in the real world you need to bend / break individual items to get the best overall solution. All engineering is compromise between various factors; without understanding you can't hope to get the balance right. According to the precise circumstances the actual "answer" may be different because of slightly diffferent weightings between the factors. Not just in engineering- look at the different classes of different food supermarkets that exist and the various "ranges" each offer and the reported change in fortunes of some of the players in recent weeks as the economic outlook has changed!

4. Any signalling the layout decision needs to come to a balance between "safety" , "operability", "economy". Safety comes first but only to a limited extent; the ultimately safe train is one that is stationary on a track reserved for itself. However that is not useful; unless a railway provides an effective means of transport, sufficiently fast, sufficiently reliable and at an affordable price then people won't use it and travel by other, probably more unsafe, means of transport.

5. Now to the specific (though recognise that the above WASN'T off topic but "setting the scene" as the way in which you asked suggested a lack of comprehension at a higher level). Think of the risk of train stopping on viaduct; is it viaduct collapse or being long term weakened from long term support of the extra weight? is it train being blown off in a gale? is it the fact that a passenger may think that they have stopped at the station and then attempts to get off onto what they think is the platform but turns out to be the viaduct parapet wall? In most cases I think that the last is the most relevant; or rather would be in the dark and where the passenger can open the door (i.e. not power operated, not centrally door locked)- in other words it is probably a risk that existed in the UK when many trains stopped at dimly lit stations in rural areas and there was no door control- far less of an issue now since 2000. Heritage lines (and just a few specials run on NR) do feature such operation but rarely run in the dark and there are certain other mitigating factors; some actually deliberately stop evening dining trains for a long time at such locations so that the clients can have a good view when eating at their tables, but they are scarcely likely to abandon the train in haste during their meal!
However do not forget the poor maintainer who needs to access. If equipment (not just signal but associated track equipment) is on viaduct (where can location case be put?) then how do they get to work on it safely? Almost certainly needs to stop traffic to be able to do so- lose capacity unless long gaps in timetable. Do all maintenance at night?- inefficient and other safety risks. What when need to access immediately because of a fault arising? None are insuperable but all are disadvantages [think of the Underground and how they address these issues]. If placing equipment in such undesirable locations, at least let the examiner know that you have considered and have mitigated as much as you feel circumstances allow.

6. So IF you really needed to, then it would be OK to place a signal at 1300. However it is really stupid place given that you are stopping a train on the botttleneck section- the one short bit of single line on what is otherwise a double track route. What is the advantage of stopping it there?- better to hold prior to the viaduct on the double line portion. ALSO READ THE NOTES- you are supposed to be providng "standage for freight between station C and the commencement of the single line"- this is actually a very tight fit and there has been correspondence on this subject on the Forum. Basically I'd put Down signals as close to the switch diamonds as I could and similarly Up signals at 1400 just clear of the convergence and work out what standage could be provided. Declare this maximum, note that it is non compliant to client's aspiation and state they have choice between accepting it or persuading P'Way to move the single lead closer to the viaduct.

If you did want (i.e. think that the traffic description suggests that it is needed) a signal to allow a second train to be brought up close behind the one(s) stopped on the branch awaiting admission to the station, I'd put its overlap to be at the IRJs positioned at 1400 and the signal an overlap length (hence nominally 180m) from there and thus just onto the viaduct (bad for maintenance but not very bad) provided that minimum braking were respected, otherwise to the minimum braking distance or specify special aspect level controls as a closing up signal.


I hope this illustrates the thought process that you should be going through- signallling the layout is not just a matter of "painting by numbers" and plonking a few signals down on the plan to some simple "black and white" rules that are set in stone!

PJW
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#7
Thanks Peter.

(UK Mainline Practice c2000)

Whilst I was unhappy placing a signal a 1300m, the reason I was considering this was due to the operating constraint 'Empty passenger trains shunt between all platforms and the Stabling Siding at C'.

To take an empty train from Station C (DOWN MAIN) platform, it was my intention to take it down the DOWN VALLY BRANCH and then come back using a signal at 1300m to the Branch Platform via the UP VALLEY BRANCH before finally shunting into the Stabling Siding.

The only other way that I could see of performing this move was to shunt the empty train 'bang road' up the DOWN MAIN, and perform successive shunt moves first to Station C (UP MAIN) platform, then down the UP VALLEY BRANCH and finally shunt back to the Branch Platform, or the Up Siding, before moving into the Stabling Siding.

What would you consider to be the most effective way of performing this move?

Thanks

Paul
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#8
Surely you could put just a IPL at 1300m and use it as a preset shunt for main routes along the DOWN VALLEY BRANCH?

There should be no shunt moves up to such a signal over the viaduct and therefore nothing will stop at it!

To add to this...in my attempt I put main signals at the convergence to the viaduct (as close as possible for standage) but also put main signals at the UP side of station C approaching the branch, this only gives approx 600m signal spacing against a calculated minimum signal spacing of 760m for 4-aspect sequence, can I do this if I make the arguement that the trains will be traversing the junction at on 40km/h and will be approach controlled MAY-FA (33% of 120km/h) if the protecting signal at the viaduct is OFF (therefore no need for braking), and MAR if the same signal is ON (due to Colwich control)?

Also never put full signals in DOWN direction of the VALLEY BRANCH lines as it was only due for standage and a shunt movement out of the branch line up to the next main signal would suffice. This cuts down on the full overlap over the main lines. Or am I being too simple with this?
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#9
I have had a private message detailing a mistake I've made but also will explain my thoughts a little clearer. If only everyone was willing to post publicly - we'd probably get a whole lot more answers.

I made the mistake of including MAY-FA in the last post as I thought the linespeed is 120km/h but it's actually 140km/h so would probably just be MAR.

The other comment was in respect to the standage. My thoughts to achieve maximum standage was to have only a IPL on the exit of the branch rather than a main signal to eliminate the overlap. This leaves two options to getting a freight train into the down valley branch - 1. have a shunt route over the viaduct up to the IPL, or, 2 - a main route up to the station then a repelling move back.

As PJW mentioned above....it's not black and white. Just my opinion that's all!
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#10
FOR CONSIDERATION:

Down Valley Branch to Station C

My min SBD for the Branch lines is 772m and max 1025m. Would it be possible to place a main aspect on the Down Valley Branch at say 660m and then place a signal on the bi-directional Down Valley section at around 1780m. Obviously slightly overbraked, but it would allow freight to be run right up to the Switch diamonds and held there. Standage would be limited as Peter previously mentioned. A sub signal provided with the main aspect at 1780m would then allow facilite a shunt move into the station area.

Station C to Down Valley Branch

A PL at Station C (DOWN MAIN) platform would then permit a shunt move onto the bi-directional Down Vally Branch. A main aspect placed at 1400m would then allow any freight standing to be signalled across the viaduct to the Up valley Branch.

Would this work or I'm I missing something?
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