09-01-2011, 11:40 PM
(09-01-2011, 10:23 PM)interesting_signal Wrote: Ok, thanks for the explanation.
One other thing I was unsure of:
For the down direction signals 104 & 106 which lead to the branch line, the model answer only shows the green aspect with the appropriate JI, whereas I showed Y and YY (with JI) too. Is it wrong to include these? (There is no information about the next signal on the branch, so I assumed 4 aspect signalling continued).
What we can see is that there are no signals shown on the Up direction branch even though there is a junction protecting signal 121 and 171 a Y/G/Y distant for it in the Down direction, so certainly no signals for at least 1300m and indeed no hint after this (we can infer that DB continues up to the joint with DA and there is not even a signal shown at that position), so the assumption has to be that it is miles away.
If they had not shown you so much of the branch perhaps you could have argued that you thought 4 aspect signalling would continue, but since they have and there are no signals shown, then you are wrong to have made that assumption. The fact that 117 has not been given a red should be telling you that headway is not a factor along this line.
It is a question of "getting your eye in" and making the correct assumption taking into account both what is shownat is and indeed what is absent.
PJW