2012 Q7 Station layout options for turnback

[Hort]

HI, I had a go at 2012 Mod 3, Question 7, would welcome any comments.

[PJW]

I think this was a very good answer and the use of the table for answering the question was the right approach; in the exam use the blank A3 sheets for this.

I don't think it really matters that you didn't point out as adisadvantage that option1 needs a suitable margin between the traffic flows on both the Up and the Down, since effectively you do cover this as an advantage when discussing option2 and there is no value in putting the same thing down twice from the different viewpoints. I think I'd have actually put down on option1 as the need to get the timetabling "just so" and to deliver it to a high degree of precision is such that option1 in reality isn't likely to be workable- the slightest pertubation in the traffic in one direction immediatley has a knock on for the other. If we postulate that there is another stationD at which another 5 of the original 20 trains turnback by a similar arrangement, then this makes the chances of getting such arrangement to work at all very low indeed. Hence the verdict is that option1 just not suitable for the regular partial reversal of service; it is a layout that might work i
a) f for engineering work the service is suspended beyond B and all trains reverse, or a
b) s a useful facility to turn around an occasional service that is running late or has a problem with the train that needs to be got back to the depot, or
c) there was a much lower level of turnback service amongst a succession of through trains timetabled accordingly, such as might be the case at the end of a mainline outer suburbal rather than a metro.

The thing you didn't mention at all was one elemt of passenger convenience; where will the next train to "A" go from:
option1: which side of the island platform, not ideal but not too bad;
option2: very easy always the same platform face for arrivals and departures;
option3: not too bad, doesn't really matter if the arrival platform is on the left or right of the train (but it is handy to know), again like option1 not too bad re departuresas at least it is an island latform. However if the traintype only opens doors on one side when in a bay with two faces, then it can be worse than that and if this is the case for passengers that wanted to travel beyond B to C (or indeed change to another line not shown) then it may be a need to climb stairs over a footbridge etc wich is not convenient and worrse if luggage, with children, elderly etc. May miss the next train running 3 minutes behind as could take longer than this to get to the correct platform face, particularly if unfamiliar with the station and /or it is crowded.
option4: The worst for peopel travelling into the city (which presumably most are); it is a bit pot-luck whether should join an empty trai in the bay platform hoping that it won't be too long before it departs, or whether to go to the other platform where there are 3 times as many trains, probably already full. Even if departures are clearly advertised, still the chance of a last minute change made to optimise the overall service and hence end up in the wrong place with a minimum time to get across to the other platform. Hence this is clearly the worst option from that perspective.

Otherwise I thinkthat you answered pretty comprehensively. It perhaps could have done with more clarity re how you interpreted degraded working in each case (i.e. were you considering how the layout can help / hinder when the train service is, for reasons outside of this diagram, running not strictly to timetable, or were you considering the effect of a point / track failure on the layout we can see, otr problems with a train. All are valid and ideally perhaps you should have considered each; just came across to me a bit uncertain which element you were considering.
Also if end up dumping a defective train in a bay or turnback siding then you loose that for its main use 9unless it is long enough for a second train for just that eventuality. Since option3 is not shown as a bay but a line that totally segregates the two platforms and that it will take quite a length for the to outer lines to converge to a conventional 6f spacing given how far apart they are at B, then it would look practicable to extend this line to give the additional facility on the "C" side of the dtation, on the assumption we are envisaging surface railway rather than in separate bore tunnels of course!

Overall though I think this was a very good attempt and would have been high Credit or Distinction.

An alternative way of tabulating the indfo could have been to have had 5 columns, the first one being wide and having all the text with 4 narrow columns for each of the options.
There would then be a series of rows firstly considering the various SAFETY items, then the various LINE CAPACITY etc. Then you can use the columns for each option to put a score like ++ or + or - or - - to score the options relevative to each other. Also avoids the "don't have the time to put the same / similar text down twice" issue.

HI, I had a go at 2012 Mod 3, Question 7, would welcome any comments.

[Hort]

Thanks for your comments PJW.
Just thinking about all the scenarios that can cause degraded working to structure answers to similar questions, in my opinion these can be divided into two groups; broken train or broken infrastructure.
Within broken infrastructure there are several possibilities; broken rail, subsidence, landslide, tresspass all result in a line being blocked.
Points failure can lead to a loss of functionality (i.e. trains not being able to be routed to where they need to go).
Signalling failure due to loss of power or cable fault.