26-09-2012, 08:54 AM
Apologies, Peter has in his usual attentive way beaten me to to it, but I have some more detailed comments on the yard area.
At a quick glance this looks like a good solution which should score well in the exam (if you have time to complete the layout to this level of detail)
Regarding the yard arrangements:
I have provided a scan of a quick sketch of my alternative arrangement.
1. You have rather over-signalled the headshunt/ sidings area. This isn’t technically wrong, but an example of over-provision, just like providing 4 aspect signalling where 2 aspect would suffice. The usual “UK mainline” practice for the operation of non-passenger yard areas is to be unsignalled – no track circuits, signals or powered points. All movements are directed by a person in charge “shunter”, who physically checks conditions are safe before giving verbal authorities. This is considered reasonably safe, given the very low speed of such movements and lack of passengers. There does need to be a clear demarcation between the signaller-controlled and shunter-controlled areas.The “stop await instructions” notice at the end of the A&D line is the end of the signaller-controlled area, from which point the shunter gives a verbal authority. Shunt signal 906 is the opposite interface. The other notice boards are “virtual signals” used by the shunter to regulate movements.
2 In order for a train to enter any area on a main class route (authorised with at least Y aspect, there must be train detection all through the route, a "main" exit signal and overlap or energy absorbing buffer stop. Given the requirement in the spec for signalled run-round movements, entry into the run round and A&D lines from the running lines must be on signalled routes, but equally easily on Main or Shunt class. I have chosen to provide a main class route from 1007 to 1009 (fixed red signal to terminate main class route) , but shunt class routes from 1009 and 211 to the notice board, which can serve as a shunt class route exit “signal”.
3 notice how signals 1008, 904 and the notice board have been placed clear of the pointwork, so that a train can approach any of these whilst the points are in use by other moves.
4. The required run-round moves via the down main take place via 1009, 904, 210 and 901 signals. In case there is a need to get the loco back afterwards, I’ve given 901 an additional route to 211 and to 1008, but the rest of the move via 211 and 904 uses routes which must be provided anyway. I chose to position limit of shunt 900 and its overlap to the right of 1007, so that moves to 900 do not restrict moves up to 1007 – this does make 901 a preset shunt signal, however.
5. To enable the freight trains to depart without delay, I have provided main signals 1008 and 210. 1008 only needs to be R/G because the next 2 aspect stop signal has its own distant, whereas 210 also has a route to 204, so it also needs a Y - see Peter’s explanation about no need for YY. As there’s no “fastest” route, a standard indicator is used for both main routes. 210 also needs a subsidiary and miniature route indicator for the shunt class route to LOS 900.
6. Wherever non-passenger lines interface with passenger lines there must be trap points to protect the passengers. Although the spec doesn’t say if the Run Round line is “passenger” or not, there is no need for passenger trains to use it and, crucially, the freight vehicles must be left “unattended” whilst the loco runs round. Therefore, trap poinst must be provided to protect passenger trains against a run-away freight vehicle. Points 418 naturally perform the trapping function at one interface (or strictly 417 whilst a loco enters or leaves the loco spur). However, additional trap points 412B are needed a the other interface as there are no naturally occurring point to use here.
7. Because of the restriction upon trains passing in the tunnel, this places an additional “headway” constraint. To minimise the conflict between up and down trains here, signals 1003 and 1002 are positioned with overlaps clear of the tunnel. They are not “protecting signals”, but instead to positioned to delay until as late as possible the time at which an approaching train needs a route to be set through the tunnel. 1003 and 1002 need to both be normally at red, and could either be signaller-controlled or “automatically selected” on a first-come, first-served basis.
Reuben
At a quick glance this looks like a good solution which should score well in the exam (if you have time to complete the layout to this level of detail)
Regarding the yard arrangements:
I have provided a scan of a quick sketch of my alternative arrangement.
1. You have rather over-signalled the headshunt/ sidings area. This isn’t technically wrong, but an example of over-provision, just like providing 4 aspect signalling where 2 aspect would suffice. The usual “UK mainline” practice for the operation of non-passenger yard areas is to be unsignalled – no track circuits, signals or powered points. All movements are directed by a person in charge “shunter”, who physically checks conditions are safe before giving verbal authorities. This is considered reasonably safe, given the very low speed of such movements and lack of passengers. There does need to be a clear demarcation between the signaller-controlled and shunter-controlled areas.The “stop await instructions” notice at the end of the A&D line is the end of the signaller-controlled area, from which point the shunter gives a verbal authority. Shunt signal 906 is the opposite interface. The other notice boards are “virtual signals” used by the shunter to regulate movements.
2 In order for a train to enter any area on a main class route (authorised with at least Y aspect, there must be train detection all through the route, a "main" exit signal and overlap or energy absorbing buffer stop. Given the requirement in the spec for signalled run-round movements, entry into the run round and A&D lines from the running lines must be on signalled routes, but equally easily on Main or Shunt class. I have chosen to provide a main class route from 1007 to 1009 (fixed red signal to terminate main class route) , but shunt class routes from 1009 and 211 to the notice board, which can serve as a shunt class route exit “signal”.
3 notice how signals 1008, 904 and the notice board have been placed clear of the pointwork, so that a train can approach any of these whilst the points are in use by other moves.
4. The required run-round moves via the down main take place via 1009, 904, 210 and 901 signals. In case there is a need to get the loco back afterwards, I’ve given 901 an additional route to 211 and to 1008, but the rest of the move via 211 and 904 uses routes which must be provided anyway. I chose to position limit of shunt 900 and its overlap to the right of 1007, so that moves to 900 do not restrict moves up to 1007 – this does make 901 a preset shunt signal, however.
5. To enable the freight trains to depart without delay, I have provided main signals 1008 and 210. 1008 only needs to be R/G because the next 2 aspect stop signal has its own distant, whereas 210 also has a route to 204, so it also needs a Y - see Peter’s explanation about no need for YY. As there’s no “fastest” route, a standard indicator is used for both main routes. 210 also needs a subsidiary and miniature route indicator for the shunt class route to LOS 900.
6. Wherever non-passenger lines interface with passenger lines there must be trap points to protect the passengers. Although the spec doesn’t say if the Run Round line is “passenger” or not, there is no need for passenger trains to use it and, crucially, the freight vehicles must be left “unattended” whilst the loco runs round. Therefore, trap poinst must be provided to protect passenger trains against a run-away freight vehicle. Points 418 naturally perform the trapping function at one interface (or strictly 417 whilst a loco enters or leaves the loco spur). However, additional trap points 412B are needed a the other interface as there are no naturally occurring point to use here.
7. Because of the restriction upon trains passing in the tunnel, this places an additional “headway” constraint. To minimise the conflict between up and down trains here, signals 1003 and 1002 are positioned with overlaps clear of the tunnel. They are not “protecting signals”, but instead to positioned to delay until as late as possible the time at which an approaching train needs a route to be set through the tunnel. 1003 and 1002 need to both be normally at red, and could either be signaller-controlled or “automatically selected” on a first-come, first-served basis.
Reuben