(31-05-2010, 07:48 PM)PJW Wrote: I think you were very astute when stating that there needs to be clarity of the precise intention of providing the aspect in the first place; the devil is in the detail. You demonstrated your knowledge of the UK's proposed POSA (I actually thought that it was only points in line of route from post to post that were to be detected, but not 100% sure if that is how it ended up as I don't believe we have ever actually yet commissioned one).
This weekend I was at London Bridge which reminded me that the East London Line reopened recently after rebuilding / extension / resignalling etc. The relevance is that the new signalling on the ELL features PoSAs. I believe that I am still correct in saying that Network Rail doesn't have any on its infrastructure but actually some have been commissioned. This is because the ELL has been signalled to NR standards (even though it is TfL); a somewhat bizarre situation exists: there are NR standard PoSAs even though NR itself has none and never has had any!
It may well be that the subject may be considered "topical" and again feature in this years' exam but there is little readily available information. I have done some digging to find a source and extracted some relevant information which I have slightly re-written and post as an attachment for those interested. It is interesting to note that there are what in "Continental English" would be described euphemistically as "open points".
PJW