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Where should the junction be?

Posted by Yan , 30 January 2017 · 328 views

Cornawall Polbrock Grogley P4 Engine Shed

I've been a little slow in posting a reply to the previous post due to Tredethy Wharf taking up all my spare time but hope this will explain the little dilemma I've had over my fictious Polbrock Engine Shed. This is, where should I place the junction between the up North Cornwall line and the Wadebridge/Padstow Branch?

 

Ullypug is correct in saying that the scissors crossover might bit extravagant, and that a signal track would be more suitable for this line, but I wonder if this has been seen in the bigger scheme. I have two thoughts about this end of the layout and I hope the following two (very rough) signal diagrams will help to explain.
First is a diagram for a single track through this stretch of line.
Attached Image

 

When I started to think this one through a question I had was, would the LSWR or SR have kept all four signal boxes on this stretch of line? After all the LSWR did do away with the junction box in 1907/8 and had two parallel running single tracks leaving Wadebridge. These where the up North Cornwall line and the Bodmin line.
So in a thought to simulate this approach and have two parallel lines leaving Grogkey Junction and cut out possibly two Signal boxes I started to draw up plans. I soon realised that Polbock would have needed some way of communicating with Grogley box. Today a telephone might be installed but back in 1907/8 would this have been possible? So I deemed that a Signal box would be required at Polbrock which could also be the junction box. This then created the diagram below;
Attached Image
In both diagrams the grey areas will not be part of the layout but have been included to get a full idea of each signal boes leaver frames.

 

Hope this goes some way to explain why I've introduced a scissors crossover at Polbrock but I'd welcome any further comments/thoughts about its inclusion. A resultant bonus with the second diagram is helps in the storage sidings by removing possible point work to separate a single line into storage lines.

 

Please note: these are early thoughts on the signaling for both options and I have a lot to learn so any guidance from learned gentlemen of this parish would be welcome, especially on LSWR signaling practice.






Hi Yan

the scissors makes mores sense in that context but I'm still not sure it would have been required in reality.

Polbrock's primary function is presumably to supply/service locos to Grogley?

In which case 2 reversals to get onto shed seems too many. Is the engine shed track plan based on anywhere prototypical?

In which case I'm not sure why you'd need direct access to the North Cornwall line?

You could have the junction as part of the scissors but only a single line to Grogley.

Given all the other lines are single, double line seems a bit excessive.

That said, rule no 1 applies and it depends on how intensive a service exists in your reality.

The frequency of services on the actual North Cornwall wouldn't dictate extensive works or signalling. Wasn't that why the prototype junction box wasn't replaced?

I'm not much of a railwayman but my visualisation of this part of the world is definitely 'less is more'.

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Compound2632
Jan 30 2017 21:01

My understanding is that the Board of Trade disapproved of junctions like Ruthernbridge - just a single point - much preferring junctions to be laid out as full double junctions like Grogley, even on otherwise single line. So to keep your BoT inspector happy, the entire three mile section of main line from Rutherbridge Junction to Wadebridge junction would be double. Otherwise haven't you got several short single-line sections operated by token or whatever? - particularly inconvenient for light engine movements from the shed to Grogley. I think you can find exceptions to the BoT preference in parts of Scotland or Ireland; how remote was North Cornwall?

Hmmm... Good thoughts from you both.

 

By the time the North Cornwall line reached this neck of the woods it may well be consideed a remote section of the LSWR. Looking at other junctions on the line, Dunmere was just a single point junction, unlocked by a token from Boscarne Junction. I could possibly argue that Boscarne junction was a single point junction, with exchange loop in the middle and long loop siding on the down side. As for the original Grogley Junction this was a single point junction but a reverse junction. BUT the BoT might have considerred my Ruthernbridge differently as it would have been the junction between the LSWR & GWR. So more thought required here.

 

As Ullypug states the double track might be a tad excessive for this stretch of line as it is a little out of character for the North Cornwall Line. I have also pushed the limits a little as space is at a premium on this stretch of line between Polbrock and Grogley as the river does run in close to the track bed at more than one point. But there is more space beyond Polbrock towards Wadebridge for double track so I'll go back to the drawing board and have a rethink.

 

In my universe the traffic would be similar on the North Cornwall line to Launceston as it was in the late 50's early 60's. The extra traffic would be towards Newquay/Mawgan Porth and St. Blazey both via Ruthernbridge.

 

The engine shed has been loosely based on the GWR Leamington shed.

 

Many thanks guys

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Steam_Julie
Feb 01 2017 09:13

Your leaving yourself open, by making the assumption 'the last big project'? On the subject of the junction layout, I personally prefer the scissors crossing.


 

Julie

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