2007 Mainline layout

[PJW]

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.