I know that many struggle with the complexity of swinging overlaps on Control Tables; I have attached a summary.
However one option that you might consider for the IRSE Exam is to adopt the very latest NR standards which include L2SIG30009/E450 (compliance date of 05/03/10).
I quote from section 8:
Points within the overlap shall not normally be detected.
Points required to be in a specific position to provide trapping protection to the route / overlap ....shall be detected in the trapping position unless a forward route is set through the trapping points.
Points within the overlap which provide flank protection to another route shall be proved at time of clearance by that route.
The last sentence is perhaps just a little ambiguous by not being quite explicit enough: I believe it means that the new aspect is to "prove in the new position $10" the hinge points within the existing overlap where if they failed to throw there would be conflict with its route but not where the only conflict would be with its overlap.
So goodbye the "N or R or swinging" column and the aspect level often complicated expression with multiple point combinations (but note this must still be there at the route availability level, so those of you who use CT blanks with that column used for both will need to explain with # notes)
This is a very significant change in practice that I believe few people working for / on NR have yet appreciated; I've taken a keen interest because I instigated the "Non-compliance pending standards change" for the project on which I am working. L2SIG30009/E450 is that standards change; the result of some hard work by a certain IRSE Exam examiner who obviously would "know it backwards".
Certainly simplifies things quite a lot and gives improved reliability and thus overall safety benefit (which is the real reason why it is being adopted). However you still need to get your head around counter-conditional locking and Time of Operation locking. Note also there are disbenefits of deciding to adopt "NR standards of 2010"- shunt signals have overlaps and the complicated overrun detection (but wait a year or two and this may itself have eased considerably.....)
Also if I had to bet on a particular written question coming up in module 3 in 2010, then one based upon the risks associated with SPADs and the benefits /disbenefits of proving the positions of facing / trailing / flank / trapping points within the overlap would be the one on which I'd be placing my money.
However one option that you might consider for the IRSE Exam is to adopt the very latest NR standards which include L2SIG30009/E450 (compliance date of 05/03/10).
I quote from section 8:
Points within the overlap shall not normally be detected.
Points required to be in a specific position to provide trapping protection to the route / overlap ....shall be detected in the trapping position unless a forward route is set through the trapping points.
Points within the overlap which provide flank protection to another route shall be proved at time of clearance by that route.
The last sentence is perhaps just a little ambiguous by not being quite explicit enough: I believe it means that the new aspect is to "prove in the new position $10" the hinge points within the existing overlap where if they failed to throw there would be conflict with its route but not where the only conflict would be with its overlap.
So goodbye the "N or R or swinging" column and the aspect level often complicated expression with multiple point combinations (but note this must still be there at the route availability level, so those of you who use CT blanks with that column used for both will need to explain with # notes)
This is a very significant change in practice that I believe few people working for / on NR have yet appreciated; I've taken a keen interest because I instigated the "Non-compliance pending standards change" for the project on which I am working. L2SIG30009/E450 is that standards change; the result of some hard work by a certain IRSE Exam examiner who obviously would "know it backwards".
Certainly simplifies things quite a lot and gives improved reliability and thus overall safety benefit (which is the real reason why it is being adopted). However you still need to get your head around counter-conditional locking and Time of Operation locking. Note also there are disbenefits of deciding to adopt "NR standards of 2010"- shunt signals have overlaps and the complicated overrun detection (but wait a year or two and this may itself have eased considerably.....)
Also if I had to bet on a particular written question coming up in module 3 in 2010, then one based upon the risks associated with SPADs and the benefits /disbenefits of proving the positions of facing / trailing / flank / trapping points within the overlap would be the one on which I'd be placing my money.
PJW
