Answer to 2005 Part A Q1

[greensky52]

1 In short, you mean 215 does not need locked in normal when 210A R, just we hope it stay in normal. So in this case, 128A(S)&107(M) have dangerous to be set simutaneously. In order to prevent this scenario, we need to lock 107(M) when setting 128A(S). Right?

2 Noted. I had thought that we have to consider so many things in such a short time.... Thanks.

[PJW]

1 In short, you mean 215 does not need locked in normal when 210A R, just we hope it stay in normal. So in this case, 128A(S)&107(M) have dangerous to be set simutaneously. In order to prevent this scenario, we need to lock 107(M) when setting 128A(S). Right?

2 Noted. I had thought that we have to consider so many things in such a short time.... Thanks.

I mean that either
a) the interlocking could be designed to lock it normal when 210R
b) the interlocking could be designed not to lock it normal when 210R.

If option b) is chosen, there could be a need for some additional locking (which would not have been needed in option a) had been chosen). Certainly must prevent the same portion of railway being allocated to conflicting routes simultaneously, but there is more than one way of achieving this aim.
Traditionally the heirarchy for locking (deriving from mechanical lever frames) is
1. Point v Point
2. Point v Signal
3. Signal v Signal.
Hence we tend to put in route locking where there is a need for locking which is not already imposed by the previous levels. There are disadvantages with point v point locking and hence in the modern context we often decide not to implement it and therefore have a greater need for route locking.

Therefore in short having decided that don't want to be able to set 107A(M) and 128A9S) simultaneously, look to see if there is point locking that would prevent; if there is not then you need to show route locking.