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TC Endings & bi-directional signalling

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TC Endings & bi-directional signalling 04/05/2024 at 16:44 #156192
DaveHarries
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Greetings all.

These pictures show parts of the Basingstoke ASC (Salisbury to Exeter panel in the Chard Junction area and there is bi-directional signalling in use.

https://photos.signalling.org/picture?/336/category/31-west_of_england_panel
https://photos.signalling.org/picture?/337/category/31-west_of_england_panel

What would be the way of knowing where the track circuits end for SE4759 as opposed to the one for SE4762 if this was converted to a VDU-based SCC layout? Am I right to presume that the TC break after SE4769 is for that signal but the TC breaks to the left of the crossing are for SE4760 & SE4762 if the yellow buttons at those signals are not used?

Cheers,
Dave

Last edited: 04/05/2024 at 16:59 by DaveHarries
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TC Endings & bi-directional signalling 04/05/2024 at 20:16 #156195
Steamer
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The white dots indicate the limits of the overlaps, with some labelled ROL which presumably are the limits when the warner exit button is used. It looks like the full overlaps extend to the signal(s) applying in the opposite direction while the reduced overlaps stop short of the points.
"Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q)
Last edited: 04/05/2024 at 20:18 by Steamer
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TC Endings & bi-directional signalling 04/05/2024 at 21:04 #156196
TUT
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ROL is indeed Reduced OverLap
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TC Endings & bi-directional signalling 05/05/2024 at 20:45 #156209
DaveHarries
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Steamer in post 156195 said:
The white dots indicate the limits of the overlaps, with some labelled ROL which presumably are the limits when the warner exit button is used. It looks like the full overlaps extend to the signal(s) applying in the opposite direction while the reduced overlaps stop short of the points.

Many thanks. Also what would be the TC ending for SE4679 in this photo? This one isn't on an ROL so if you set a route from SE4677 to SE4679 would the circuits be lit all the way to the other side of the junction into the up siding or would the route stop immediately before the footpath crossing? It is never likely to happen but I sometimes wish I had a replica panel to find this out for myself.
https://photos.signalling.org/picture?/321/category/31-west_of_england_panel
https://photos.signalling.org/picture?/322/category/31-west_of_england_panel

For anyone wondering I did a mockup of this when we had the mockups thread active and I have decided to try and rebuild that mockup by adding the TC breaks in among other things.

Dave

Last edited: 05/05/2024 at 20:48 by DaveHarries
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TC Endings & bi-directional signalling 05/05/2024 at 20:50 #156210
Steamer
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DaveHarries in post 156209 said:
Steamer in post 156195 said:
The white dots indicate the limits of the overlaps, with some labelled ROL which presumably are the limits when the warner exit button is used. It looks like the full overlaps extend to the signal(s) applying in the opposite direction while the reduced overlaps stop short of the points.

Many thanks. Also what would be the TC ending for SE4679 in this photo? This one isn't on an ROL so if you set a route from SE4677 to SE4679 would the circuits be lit all the way to the other side of the junction into the up siding or would the route stop immediately before the footpath crossing? It is never likely to happen but I sometimes wish I had a replica panel to find this out for myself.
https://photos.signalling.org/picture?/321/category/31-west_of_england_panel
https://photos.signalling.org/picture?/322/category/31-west_of_england_panel

For anyone wondering I did a mockup of this when we had the mockups thread active and I have decided to try and rebuild that mockup by adding the TC breaks in among other things.

Dave
4679 is a shunt signal so is very unlikely to have an overlap. The dot at the right hand end of TC CHL appears to be one of 4680's overlaps.

"Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q)
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TC Endings & bi-directional signalling 05/05/2024 at 23:09 #156212
pedroathome
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Steamer in post 156210 said:
DaveHarries in post 156209 said:
Steamer in post 156195 said:
The white dots indicate the limits of the overlaps, with some labelled ROL which presumably are the limits when the warner exit button is used. It looks like the full overlaps extend to the signal(s) applying in the opposite direction while the reduced overlaps stop short of the points.

Many thanks. Also what would be the TC ending for SE4679 in this photo? This one isn't on an ROL so if you set a route from SE4677 to SE4679 would the circuits be lit all the way to the other side of the junction into the up siding or would the route stop immediately before the footpath crossing? It is never likely to happen but I sometimes wish I had a replica panel to find this out for myself.
https://photos.signalling.org/picture?/321/category/31-west_of_england_panel
https://photos.signalling.org/picture?/322/category/31-west_of_england_panel

For anyone wondering I did a mockup of this when we had the mockups thread active and I have decided to try and rebuild that mockup by adding the TC breaks in among other things.

Dave
4679 is a shunt signal so is very unlikely to have an overlap. The dot at the right hand end of TC CHL appears to be one of 4680's overlaps.
Please correct me if I'm wrong. The panel went in somewhere around the early to mid 2010s? More recent signalling schemes have had overlaps on shunt routes (See Gresty Lane for example).

https://photos.signalling.org/picture?/328/category/31-west_of_england_panel

I suspect the overlap marker at Signal 4717 is the overlap for shunt signal 4712.

On the photo of 4679 / 4680, it woulden't surprise me if the overlap between CHK / CHL tracks was for both the main and shunt signals in their respective directions

James

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TC Endings & bi-directional signalling 05/05/2024 at 23:53 #156213
DaveHarries
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pedroathome in post 156212 said:
Please correct me if I'm wrong. The panel went in somewhere around the early to mid 2010s? More recent signalling schemes have had overlaps on shunt routes (See Gresty Lane for example).

https://photos.signalling.org/picture?/328/category/31-west_of_england_panel

I suspect the overlap marker at Signal 4717 is the overlap for shunt signal 4712.

On the photo of 4679 / 4680, it woulden't surprise me if the overlap between CHK / CHL tracks was for both the main and shunt signals in their respective directions

James

Basingstoke ASC (West of England) panel was commissioned into use in 2012 and resulted in the closure of the boxes at Gillingham (Dorset), Templecombe, Yeovil Junction, Chard Junction and Honiton. The pictures in these links are the most recent ones I can find anywhere but if newer photos appeared online showing every part of the panel close-up I would correct anything which needed correcting. As it is, I don't know.

Dave

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TC Endings & bi-directional signalling 16/05/2024 at 17:25 #156294
DaveHarries
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Here's another goodie: restricted overlaps (ROL) in both directions by the looks of it. My guess, not knowing the setup, would be that the ROLs are for 4773 & 4777 whereas the circuit breaks immediately after those two signals would be for 4768 whose button has a surround which is yellow as well as red and the break next to 4768 would be for either 4773 or 4777 if the yellow buttons for those were not pressed.
https://photos.signalling.org/picture?/338/category/31-west_of_england_panel

Dave

Last edited: 16/05/2024 at 17:41 by DaveHarries
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TC Endings & bi-directional signalling 16/05/2024 at 18:19 #156296
TUT
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The red and yellow bezel is to indicate that main and subsidiary routes may be set from that signal (note the position light underneath for the route to 4764 and the siding). Over time, as the spares dry up, one occasionally finds that standards like this are not universally adhered to.

Yes I should think the reduced overlaps apply to 4773 and 4777, with their full overlap being at 4768. This mimics the traditional rules that do still generally apply on electric token block and tokenless block lines, but are not a general requirement for TCB. These rules require that when two trains are approaching a crossing place from opposite directions, you must keep both home signals at danger. When the first train to arrive has stopped you can then clear the signal to allow it into the loop. Once it's stopped in the loop you can then clear the signals for the train in the opposite direction. You can see how if you had already cleared 4769 into the loop with a full overlap, that would actually prevent you from signalling a train up to 4768 and thus allowing it to approach the loop in the opposite direction. But what you can do instead is select the reduced overlap and then a train can be signalled to 4768 at the same time (whether before or after the route from 4769 is set). You can further see how if a train has already been signalled up to 4768 you won't be able to select the full overlap. Thus, with the reduced overlap selected, 4769 will surely be approach controlled, so a train approaching 4769 will not get the distant and may be checked further at 4769, thus preventing it from approaching the loop exit signals (4773 & 4777) at excessive speed while another train is signalled up to 4768 approaching at full speed in the opposite direction.

I think it highly unlikely there are reduced (not restricted) overlaps in both directions, however. Usually when a reduced overlap is selected the previous signal will be held at danger in the manner described so that an approaching train will have its speed checked. The signal will then release to allow the train to approach the next signal from a nice low, safe speed. That doesn't work too well if the previous signal is several miles away at the other end of a single line block section and there's a main aspect disant in between! Now granted in the old days of the warning arrangement on absolute block it did use to be the case that if a train had already passed the signal box when it was accepted under the warning (and therefore there was no way to exhibit a green hand signal or verbally instruct the driver) the train would be brought to a stand at the section signal, which would then be lowered and the driver would understand from that that the section was clear to the next home signal but the station or junction ahead was blocked. But that isn't really a thing with TCB and MAS.

Last edited: 17/05/2024 at 12:02 by TUT
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The following users said thank you: DaveHarries, mldaureol