17-09-2013, 09:43 AM
I actually think this question is a bit too limiting and therefor difficult to get good marks.
Item 1 is the obvious one; items 2 &3 are fundamentally the same as each other, the only difference whether or not it involves a SPAD and potentially therefor potentially a slower speed incident. Your 4th is about trailing points which are outside question scope- however it did add value since it is the only time you mentioned operational impact and damage in addition to collision / derailment (which are really the events which lead to the risks including the above, injury, death etc.)
I think that to try to get some more content that I'd have looked at the various scenarios; e.g. perhaps the signal is a platform starter (often is as generally try to avoid placing points immediately beyond signals but this is a circumstance when unavoidable)
a) booked train may not have departed on schedule, signaller may then have replaced its signal to danger but without reaching a proper understanding with the driver who had previously seen it off and was about to move,
b) diesel / oil on rails from leakage from previous trains meant that the rails were slippery and a driver running into the station intending to stop then suddenly encountered low adhesion so overshot a short distance and encountered points,
c) driver given "right away" by guard / platform dispatch staff who had failed to check signal was cleared for train departure and driver also fails to check aspect,
d) driver of through train but to take the lower speed diverging route is expecting the signal to be approach released as gets close to it as previous experience suggests it will, only today it does not.
Hence already we have 3 type different forms of SPAD and for which the later part of the question can discuss interlocking / procedural controls.
You may feel that I am talking more about SPAD than the points, but isn't this the risk scenario; otherwise we are really restricted to discussing signalling wrong side failures (or of course the situation in which such locking is not regarded as necessary).....whereas these should be mentioned of course, I doubt whether it would be easy to get the marks for the question mainly from this. Detection of points in line of route is really a "given" so that would itself be holding the signal to red, hence the only "engineering judgement" type debate is about detection of points within the overlap, application of "time of operation locking" etc. and there is not much here to talk about I feel).
To me it is the existence of the set of points immediately beyond the signal that converts what might otherwise be a relatively low risk event into something potentially much worse.
Your answer re item 1 was OK; useful had you pointed out that the provision of flashing aspects could be helpful in reducing the risk associated with the driver making the incorrect assumption of last minute approach release and indeed explaining that current practice for MAR is to release as soon as possible given route indicator sighting rather than perpetuating previous practice of trying to hold signal at danger until train speed had been reduced to junction speed.
Items 2&3 reasonable but would have been better to tie more closely with the various different find of SPAD scenarios.
Operational impacts.
Reasonable and yes I think it was a good idea to illustrate with mechanical signalling as well as RRI since it does serve to expand the question. I can assure you that with ticket working that it is even more restrictive, with people needing to secure and padlock points on site before any inolvement authority given and that takes a very long time!
Of course item 4 is out of scope.
Item 1 is the obvious one; items 2 &3 are fundamentally the same as each other, the only difference whether or not it involves a SPAD and potentially therefor potentially a slower speed incident. Your 4th is about trailing points which are outside question scope- however it did add value since it is the only time you mentioned operational impact and damage in addition to collision / derailment (which are really the events which lead to the risks including the above, injury, death etc.)
I think that to try to get some more content that I'd have looked at the various scenarios; e.g. perhaps the signal is a platform starter (often is as generally try to avoid placing points immediately beyond signals but this is a circumstance when unavoidable)
a) booked train may not have departed on schedule, signaller may then have replaced its signal to danger but without reaching a proper understanding with the driver who had previously seen it off and was about to move,
b) diesel / oil on rails from leakage from previous trains meant that the rails were slippery and a driver running into the station intending to stop then suddenly encountered low adhesion so overshot a short distance and encountered points,
c) driver given "right away" by guard / platform dispatch staff who had failed to check signal was cleared for train departure and driver also fails to check aspect,
d) driver of through train but to take the lower speed diverging route is expecting the signal to be approach released as gets close to it as previous experience suggests it will, only today it does not.
Hence already we have 3 type different forms of SPAD and for which the later part of the question can discuss interlocking / procedural controls.
You may feel that I am talking more about SPAD than the points, but isn't this the risk scenario; otherwise we are really restricted to discussing signalling wrong side failures (or of course the situation in which such locking is not regarded as necessary).....whereas these should be mentioned of course, I doubt whether it would be easy to get the marks for the question mainly from this. Detection of points in line of route is really a "given" so that would itself be holding the signal to red, hence the only "engineering judgement" type debate is about detection of points within the overlap, application of "time of operation locking" etc. and there is not much here to talk about I feel).
To me it is the existence of the set of points immediately beyond the signal that converts what might otherwise be a relatively low risk event into something potentially much worse.
Your answer re item 1 was OK; useful had you pointed out that the provision of flashing aspects could be helpful in reducing the risk associated with the driver making the incorrect assumption of last minute approach release and indeed explaining that current practice for MAR is to release as soon as possible given route indicator sighting rather than perpetuating previous practice of trying to hold signal at danger until train speed had been reduced to junction speed.
Items 2&3 reasonable but would have been better to tie more closely with the various different find of SPAD scenarios.
Operational impacts.
Reasonable and yes I think it was a good idea to illustrate with mechanical signalling as well as RRI since it does serve to expand the question. I can assure you that with ticket working that it is even more restrictive, with people needing to secure and padlock points on site before any inolvement authority given and that takes a very long time!
Of course item 4 is out of scope.
(15-09-2013, 04:51 PM)Hort Wrote: Thanks for previous comments. I have now attempted Question 9 on the 2012 Mod 3 paper.
PJW