Rules of LNWR two doll twin signals at junctions

[PatriotClass]

Hello guys,

I am just studying British signaling to equip my layout correctly.  Thanks to some nice websites I am getting slowly through it, but I am stuck with one type of signal that I saw on LNWR pictures several times. See the one linked below! I am meaning the one in the center. It's obviously a junction signal with two dolls and both arms on same height. So it should give rule for two tracks, equal speed. I learned that ahead should be a point that splits the line in two ways. But ahead of this signal, there are two tracks joining. What's the information for the driver when the left arm is on and what's when the right arm is on? Wouldn't it be enough to install just a one arm signal?

 

I just linked the picture here, because it has copyright by the Transport Library.

[APOLLO]

Routes diverge after signal box ?

 

Brit15

[kevinlms]

47 minutes ago, PatriotClass said:

 I learned that ahead should be a point that splits the line in two ways. But ahead of this signal, there are two tracks joining. What's the information for the driver when the left arm is on and what's when the right arm is on? Wouldn't it be enough to install just a one arm signal?

 

I just linked the picture here, because it has copyright by the Transport Library.

The relevant signal can only be cleared when the points immediately in front are set, but they are really referring to a splitting junction ahead.

The signals are mechanically locked, so that a number of conditions have to be correctly set, BEFORE they can be cleared. That means that there is a least 2 sets of points in this photo before the matching signal can be cleared.

[iands]

Did the photo description say where the location was? If so it might be possible to dig up a diagram of the area that would provide an explanation of the routing from the signal (and the others). 

[iands]

6 minutes ago, iands said:

Did the photo description say where the location was? If so it might be possible to dig up a diagram of the area that would provide an explanation of the routing from the signal (and the others). 

Ignore last, just found the photo, it's at Chester.

[iands]

3 minutes ago, iands said:

Ignore last, just found the photo, it's at Chester.

.... and of course the signalling scheme plan that I have a copy of Chester is long after 1973. However, I think the major routes are pretty much the same, although now with colourlight signals. So, depending on which way the photo is looking, the signal dolls will read either to the Up Main or Down Warrington, or if looking the other way, Down Main and Down Birkenhead.

[Flying Pig]

It appears to be Chester No. 2 Box.  This sketch, from maps.nls.uk (link) shows the viewpoint, diverging routes and signalbox (arrowed):

 

[PatriotClass]

So when e.g. the left arm is on, all points are cleared for the main line and if instead the right arm is on, the points are set for Birkenhead. If the train is e.g. sheduled for Birkenhead, the driver has to wait, until the right arm gets on. So this signals are not necessarely situated in direct proximity to the physical junction. 
Please excuse me for asking some questions that are maybe not really professional for a British railway enthusiast, but in Germany this type of junction signalling is completely uncommon. On the other hand just this is beneath many other things what's faszinating me about British Rails. 

[PenrithBeacon]

I believe that because both signal dolls are the same height then both routes are thought to have equal importance. But I'm not sure!

[Flying Pig]

29 minutes ago, PatriotClass said:

So when e.g. the left arm is on, all points are cleared for the main line and if instead the right arm is on, the points are set for Birkenhead. If the train is e.g. sheduled for Birkenhead, the driver has to wait, until the right arm gets on. So this signals are not necessarely situated in direct proximity to the physical junction. 

 

The routes ahead are actually left to Warrington and right to Crewe as this is the east end of Chester station.  Note also that if you trace the route on the map I linked rather than my sketch, there are further signals (marked SP for signal post) just beyond the bridge along the left branch and just before it along the right branch.  The signals in your photograph when clear indicate that the points are set (and locked where necessary) only as far as these signals.

[iands]

8 hours ago, PenrithBeacon said:

I believe that because both signal dolls are the same height then both routes are thought to have equal importance. But I'm not sure!

I think both routes have "equal speed" (at that point) rather than "importance". 

[PenrithBeacon]

1 hour ago, iands said:

I think both routes have "equal speed" (at that point) rather than "importance". 

Not so sure, speed signalling was a big no-no in Britain until fairly recently.

[kevinlms]

2 hours ago, iands said:

I think both routes have "equal speed" (at that point) rather than "importance". 

I believe that the actual speed limits may possibly be different, but will be both rather slow.

The drivers are expected to know the actual speed limit, for each signal. 

[kevinlms]

30 minutes ago, PenrithBeacon said:

Not so sure, speed signalling was a big no-no in Britain until fairly recently.

Only the old LMS signalling in the Mirfield area.

[phil-b259]

2 hours ago, iands said:

I think both routes have "equal speed" (at that point) rather than "importance". 

 

Though its quite normal for the 'lesser' route to have a lower speed that is simply a happy coincidence.

 

The whole basis of UK signalling principles is NOT speed!

 

We tell the drivers the ROUTE they are to take and its up to them to regulate their speed based on route knowledge.

 

This differs from German practice say where signals give an indication of the SPEED a driver should be doing and not which route they will be traveling on. You don't get route indicators fitted to signals in Germany for this reason.

 

Its also worth noting that in some places they started off using the British Route based mechanical signalling but have adopted Speed based signalling when modernising and going for colour light signalling / track circuit block all overseen by large centralised control centres.

[phil-b259]

58 minutes ago, PenrithBeacon said:

Not so sure, speed signalling was a big no-no in Britain until fairly recently.

 

Its still a 'big no-no' as you put it and UK signalling standards do not allow for it to be installed.

 

The only place it was adopted in the UK was around Mirfield by the LMS as a trail. This got replaced by BR with conventional UK signalling (route based rather than speed) in the 1970s / 1980s

[Grovenor]

17 hours ago, PatriotClass said:

So when e.g. the left arm is on, all points are cleared for the main line and if instead the right arm is on, the points are set for Birkenhead. If the train is e.g. sheduled for Birkenhead, the driver has to wait, until the right arm gets on.

Note to avoid future confusion, describing the signal as 'on' in British practice means that it is showing a danger aspect, ie is horizontal. When pulled to show that a movement may be made the signal is described as 'off'. So each time you say 'on' above you should have said 'off'.

[iands]

6 hours ago, PenrithBeacon said:

Not so sure, speed signalling was a big no-no in Britain until fairly recently.

To clarify, I wasn't suggesting "speed signalling" per se, simply that whichever route was taken (in the photo in the OP) the speed would/could be the same, e.g. 10mph. 

[62613]

5 hours ago, phil-b259 said:

 

Its still a 'big no-no' as you put it and UK signalling standards do not allow for it to be installed.

 

The only place it was adopted in the UK was around Mirfield by the LMS as a trail. This got replaced by BR with conventional UK signalling (route based rather than speed) in the 1970s / 1980s

Around 1968, I think

 

[Michael Hodgson]

18 hours ago, PatriotClass said:

So this signals are not necessarely situated in direct proximity to the physical junction. 

 

The signals are placed where you would want the train to stop, which is not necessarily immediately at the toe of the facing point concerned.  You would not want a train stopped where it would block other movements on other lines, so the signal could be a little further back clear of some other pointwork.

[kevinlms]

18 minutes ago, Michael Hodgson said:

 

The signals are placed where you would want the train to stop, which is not necessarily immediately at the toe of the facing point concerned.  You would not want a train stopped where it would block other movements on other lines, so the signal could be a little further back clear of some other pointwork.

Back in the 'bad old days' of early signalling, before interlocking, some railways put a central signal for a junction on the roof of a signal box. The driver had to know how far short of the signal he had to stop, so that points could still be changed.

[TheSignalEngineer]

2 hours ago, iands said:

whichever route was taken (in the photo in the OP) the speed would/could be the same, e.g. 10mph. 

Generally arms would be the same height for routes where the speeds differed by no more than 10mph. 

[beast66606]

The signals are Chester No.2 up starting, the date appears to be 1960s / early 1970s - there was a double junction by the box for the main lines which the right hand pair of signals read over and there were connections for the bay lines, the left hand most signal in the photograph controls the departure from one of these, there was a lot of slotting between the boxes - until No.1 was abolished in the early 1970s from when No.2 signalled the whole area - I can't remember if these signals were dual controlled from both boxes or just No.2. I have diagrams for both and will try and find them over the weekend to clarify.

[phil-b259]

3 hours ago, TheSignalEngineer said:

Generally arms would be the same height for routes where the speeds differed by no more than 10mph. 

 

Again, thats more of a coincidence of the route importance aligning with speed, rather than speed being the governing factor.

 

For example the principle direction on the down ECML from London is Yorkshire and Scotland - turning right at Hitchin is a lesser route so got shorter arms in semaphore days for THAT reason and not the speed of the divergence

 

Similarly when the two track section becomes 4 tracks again north of Welwyn, the slow lines are clearly the lesser of the two so gets a shorter post.

 

Approaching Kings Cross on the other hand from the north all platforms have equal status so will have arms at the same height.

 

There were places away from main lines where the speeds were identical but one route was quite clearly of lesser importance - so it got a shorter post.

 

https://www.pinterest.co.uk/pin/517280707194091898/

 

This photo of the signal at the divergence of the Highbridge and Bath lines on the S&DJR is one such example - the lower speed tightly curved route was in fact the 'main line' to Bath so gets the taller post while the 'branch' although being straighter and thus permitting higher speeds is given a shorter one detonating its role as the secondary route.

 

If the height of the posts was related to speed then the situation would be reversed!

Edited August 18, 2021 by phil-b259

[Innerhome]

The HMRS website has a couple of photographs of the diagram at Chester No 2 - unfortunately not very clear and they don't cover the full diagram - one showing the layout at the platform ends and one the junctions between the Crewe and Warrington lines. The photos are dated 1977 - so I think some rationalisation has already taken place.