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2012 Paper Attempt- Facing Points
#1
Morning All,

Please see attached Module 3, 2012 Paper Question 9 attempt regarding facing points beyond a protecting signal.

Comments & questions welcome.

Many thanks


Attached Files
.pdf   Module 3 2012 Paper Question 9 Attempt.pdf (Size: 2.35 MB / Downloads: 87)
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#2
No attachment!
Le coureur
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#3
(19-09-2018, 11:09 AM)Jerry1237 Wrote: No attachment!

Well spotted- now added!
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#4
I was going to respond to the answer provided but feel it isn't my area and would be better to hear from others on the forum.

Al I will say is the question is suitably ambiguous and the question does state "short distance beyond" which clearly has significance.
Le coureur
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#5
The phrase "short distance beyond" is significant and the final part of your answer where the points are within the overlap is probably the one to focus on.
We have to assume that a train which has passed a signal at danger will not get further than a certain distance - normally the length of the overlap - otherwise where would we stop in controls and protection.
So, let us assume we have a set of facing points in the overlap, what are the hazards?
The first is that if we have a train approaching and the points are detected N or R (with a time to move provision) then if they are called and don't detect we have the risks of a brown trouser moment for the driver when the signal which was yellow goes to red in front of them.
The other hazards seem to need a SPAD to occur first. If we allow an overlap to swing then we have to accept that it is possible that although the points were detected in one position after the move they may not be detected. We then have three scenarios to consider - they did not move (probably still safe to run over), they moved and are sufficiently over to be safe but the detection failed, or they are mid throw. In the event of a SPAD (which is likely to be at a low speed with TPWS, etc.) then only the last option leads to a direct hazard and it is quite an unlikely event. One can also argue that a set of points mid throw is no different to a wide to gauge set of traps and quite a good retarder!
The other control which is still applied is Time of Operation Locking where if the train is close to the signal you don't allow the points to be called to move in case the SPAD occurs and the points are mid throw. Given that points take less than 5 seconds to move and SPADs are rare, is the control a good one - discuss!
Part 2 of the question allows discussion of banning swinging overlaps or use of TOOL and the impact on performance particularly where the points need to be swung to provide flank protection to other routes.
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