Indeed; I was very much aware and thus I worded it as what I hoped was an open question to provoke the thought process.
I expect the scenario was intentional and that the examiners expected the candidate to justify it one way or another within the explanation they specifically called for as part of this question.
Broadly after Colwich, there is concern about the driver misunderstanding the meaning of FY. The exception re the auto signal is because:
1. It would often be impracticable (excessively costly) to implement
2. The risk associated with a SPAD at such a signal is low (not very likely to be at red anyway, at worst a rear-end collision).
The exception re a passenger platform is because (and it is really assuming a platform with pointwork beyond it in the station throat rather than the plain line type station that we have here) there are quite a lot of sites when the operating department really want a flashing aspect to signal into the platform loop line (Birmingham International station springs to mind). However it is likely that the exit signal will be at red since another train may being signalled out of the parallel platform or indeed there is a fast train just behind the one entering the loop which is about to overtake it. Balance of Safety and Operability again; although to be fair it can also be argued that the risk of confusion re what a FY might mean isn't significant if the driver is expecting to stop at the station anyway whatever aspect sequence is given.
It is my experience that we [OOPS sorry NR, the railway I now work for doesn't have any flashing aspects and is trying to get rid of lineside signals altogether] generally apply the control unless there is a good reason not to do so; hence even though the signal is an auto, if it were SSI then would almost certainly do so. Every one is quite risk adverse and it is sometimes just easier to do it than run the risk someone else will come along just before commissioning (such as a CIP) and decide that it should have been imposed.
I expect the scenario was intentional and that the examiners expected the candidate to justify it one way or another within the explanation they specifically called for as part of this question.
Broadly after Colwich, there is concern about the driver misunderstanding the meaning of FY. The exception re the auto signal is because:
1. It would often be impracticable (excessively costly) to implement
2. The risk associated with a SPAD at such a signal is low (not very likely to be at red anyway, at worst a rear-end collision).
The exception re a passenger platform is because (and it is really assuming a platform with pointwork beyond it in the station throat rather than the plain line type station that we have here) there are quite a lot of sites when the operating department really want a flashing aspect to signal into the platform loop line (Birmingham International station springs to mind). However it is likely that the exit signal will be at red since another train may being signalled out of the parallel platform or indeed there is a fast train just behind the one entering the loop which is about to overtake it. Balance of Safety and Operability again; although to be fair it can also be argued that the risk of confusion re what a FY might mean isn't significant if the driver is expecting to stop at the station anyway whatever aspect sequence is given.
It is my experience that we [OOPS sorry NR, the railway I now work for doesn't have any flashing aspects and is trying to get rid of lineside signals altogether] generally apply the control unless there is a good reason not to do so; hence even though the signal is an auto, if it were SSI then would almost certainly do so. Every one is quite risk adverse and it is sometimes just easier to do it than run the risk someone else will come along just before commissioning (such as a CIP) and decide that it should have been imposed.
(02-09-2011, 08:05 PM)Peter Wrote:(02-09-2011, 07:48 PM)PJW Wrote: In particular do you consider it would be appropriate to display a flashing aspect sequence at a time that 121 is at red?
I was going to say the same thing, but then I looked at GK/RT0045 which says in section 5.2.3.6
Quote:A flashing aspect sequence shall only be displayed when the approaching train is detected to be in a position that is compatible with the required reading time of the junction distant signal that displays the flashing single yellow aspect and one of the following applies:
a) The first signal beyond the diverging junction is a controlled stop signal that is either one of the following:
i) Displaying an OFF aspect
ii) Displaying an ON aspect and a forward route is set
iii) Displaying an ON aspect at the end of a loop line or platform line where all trains are expected to stop
b) The first signal beyond the diverging junction is an automatic signal
c) The first signal beyond the diverging junction is an isolated distant signal
d) The train protection system is configured to mitigate the SPAD risk at the first stop signal beyond the diverging junction.
Given the layout beyond 121, I assume that condition b) applies. a)iii) may also apply.
PJW