Questions regarding Swithland Sidings

[Phil25]

Hello, I have a question regarding this GCR Swithland Sidings signal box diagram. I've seen many diagrams but this one is a bit unusual.

https://www.flickr.com/photos/loose_grip_99/8089370101 - link to flickr website, on which someone posted a picture of Swithland Sidings diagram

I was wondering why is there a slot below distant 32 and what does the letter 'T' mean, which also appears next to down main advanced starter. I don't usually see slots associated with the same signal box.
My second question is why is there no starter signal for the branch, as you can see only two shunt discs. Also if a train was to go from Rothley to branch (and vice versa) would it simply be shunted?
I would appreciate a response from someone who knows GCR.

 

[Gloster]

I think that the T in a circle indicates that a telephone (to the box) is provided there. I presume that the branch is worked as a siding so a disc is sufficient to give authority to go on to it, but coming off the branch you are going on to a running line and the practice is to provide a full signal for this.

 

[merry]

To answer the question about 32 being slotted: 32 is the Down inner distant below Down Home 33, the outer distant 31 being slotted with Rothley Starter/Section signal (RY17).
A Distant below a Stop signal must not be 'off' unless the stop signal is also 'off' and the slot ensures this, even if the home is pulled but does not respond for whatever reason. It's a kind of secondary interlocking at the signal post.
Simlarly, Swithland Up Distant 43 is slotted with Up Outer Home 42. In the Up direction, there is also an Auto Distant colour light. RY Up Distant (RY1) is located under 39 AND 40 (i.e. has 2 arms), and slotted with BOTH. It's a heavy pull (as ever, there is a knack to it!)

Why so many distants, you ask? Well, it allows a controlled approach to the signals when trains are running close together, and given the curvature of the line. In the Down, the outer distant 31 can be pulled to let a train departing Rothley (from RY17) know Dn Home 33 is clear, but if 32 Dn Inner Distant is On, the drive knows that Dn Starter 34 will be at danger (34 might be cleared when nearly at as stand, to allow them to draw towards Dn Section Signal 35 if the section towards Quorn is still occupied.). This is helpful for safely managing the train speed, and optimises timings.
An Up train will see the auto distant at single yellow if Inner Home 42 is On, double yellow if 42 is Off, but Up Distant 43 is On (meaning Up Starter 40 is On), and a green auto distant only if Section Signal 39, Starter 40, Inner Home 41, Oute Home 42 and Distant 43 are all Off.

Note that a Down train is not out of section from Rothley until it has passed 34 (or stands at 34 while points 26 are reversed and the loop is clear to 27). An Up train is out of section from Quorn when it has fully passed 41.
Hope that answers your questions - and some of the likely follow-on ones!

For the branch, this picture dates from before the branch signalling was modified; there is now a running signal for 51, not a disc, and some other changes allowing the bransch to be used for passenger services.

Disclaimer: I don't sign Swithland, so this is all my understanding from normal operating practice in this location.

Edit to answer question about the branch.

 

[Phil25]

Thank you for your reply, Merry
I'm glad that you've explained some of the stuff to me, I guess I kind of expected that answer when it comes to the slotted distants, but this question came to my mind mostly because... general rule is to not depict distants slotted with a main signal on the same signal post (I swear I've seen proof of this somewhere but can't find it so instead I'm providing a networkrail document below). I guess they are just extra-careful.

Why so many distants, you ask? Well, it allows a controlled approach to the signals when trains are running close together, and given the curvature of the line. In the Down, the outer distant 31 can be pulled to let a train departing Rothley (from RY17) know Dn Home 33 is clear, but if 32 Dn Inner Distant is On, the drive knows that Dn Starter 34 will be at danger (34 might be cleared when nearly at as stand, to allow them to draw towards Dn Section Signal 35 if the section towards Quorn is still occupied.). This is helpful for safely managing the train speed, and optimises timings.

Having more than one distant signal per up/down line that is also worked by the same signal box is indeed quite uncommon.

An Up train will see the auto distant at single yellow if Inner Home 42 is On, double yellow if 42 is Off, but Up Distant 43 is On (meaning Up Starter 40 is On), and a green auto distant only if Section Signal 39, Starter 40, Inner Home 41, Oute Home 42 and Distant 43 are all Off.

At this point I may be getting a bit off topic but i think that these types of distants are only capable of displaying a single green/yellow, unless it's just the case for colour distants worked from the signal box. I've played a few simulations and they seem to depict colour distants in this way, after all it's two aspect signalling and double yellow is associated with four aspect signalling. If they actually have double yellow that makes it so much easier!

Note that a Down train is not out of section from Rothley until it has passed 34 (or stands at 34 while points 26 are reversed and the loop is clear to 27). An Up train is out of section from Quorn when it has fully passed 41.
Hope that answers your questions - and some of the likely follow-on ones!

Yes that's a clearing point, they need quarter of a mile clear after their first signal

For the branch, this picture dates from before the branch signalling was modified; there is now a running signal for 51, not a disc, and some other changes allowing the bransch to be used for passenger services.

Now it makes more sense!



(picture I mentioned in the beginning)

 

[LowLevel]

Having multiple distant signals (accelerating distants) was far more common when signalboxes were closer together and of course the GCR is a working museum - the London Extension had plenty of them. There is 4 aspect signalling in a fashion on the up at Swithland as the auto distant is capable of showing yellow (42 signal on, line clear to outer home only), double yellow (42 signal off, line clear to inner home) or green (all off for the up main, line clear through to block section).

With regards to diagrams, the GCR doesn't use Network Rail's parameters for that.

 

[merry]

Thanks for adding that @LowLevel.
I am informed that the GCR most closely follows GC/LNER practice, except where more modern standards are required for safe working. There are double yellow capable colour light distants like you mention at Swithland (up), Quorn (dn & up), Loughborough (dn), although the latter of course can't show green yet!
And Hotchley Hill is apparently planned to be all LNER type colour light running signals.
Edited for spelling errors

 

[Belperpete]

With mechanical signalling, there were wide variations in practice, even within the same company. The old York drawing office instructions included many differences in practices between "north" and "south", for example. As mechanical signal boxes tended to have long lives, they could well represent pre-grouping company practices. And where they were supplied by one of the signalling contractors, they might reflect that contractor's practices.