Understanding Signal Box Diagrams

[Halton Boy]

Hello Everyone

I have been all over the internet and on this site, but I cannot find the explanation I need.

Here is a typical signal box diagram:

I understand the signals like starter, home and ground disc's.

What I don't understand is what some parts of the drawing mean.

I have added letters A,B and C etc to the drawing to highlight the parts I do not understand.

Part A

Is 4 and 4 a double slip?       What is 5A and 5B? 

Part B

Is 7 a facing point lever?       What is 8 and 8 is this a cross over?  What is 5B It looks like single slip if there is such a thing.

Part C

Is this like a Peco 8 deg crossing?

Part D

Is 14 a facing point lever?   Is 15 a point linked to a trap point 15 before the engine shed to protect the running line?

Part E

Is 18 and 18 a double slip?   Is 19 and 19 the cross over? How do these relate to each other, please.

Part F

Is 20 a facing point lever.

 

I have reproduced the drawing in Anyrail below:

A,B and E are all double slips in Anyrail. 15b is a left hand trap point.

 

If A,B and E are double slips why is the drawing marked with 5-5 and 8 - 8. Why 18 -18 and 19-19?

8 is a LH point, is 8 on the double slip a form of interlocking?

19 is a RH point, is 19 on the double slip a form of interlocking?

Are the double slip at A and at B interlocked by 5 and 5?

How would an engine run from the head shunt at Engine start to the siding at engine finish? 

Is this why there is 18 -18 and 19 -19, 8 - 8 and 5, 4 - 4 and 5 at the double slips? 

I am sorry this is such a lot to answer, but I am stumped, you are my only hope.

Thank you for your help.

 

[BR traction instructor]

A & B are single slips, (apologies for error).

 

C is a diamond crossing.

 

D is a trap point…passenger lines must be protected from the risk of runaway wagons, other vehicles etc causing an obstruction. The lines from the Goods shed & both of the other sidings should be similarly protected (an expensive layout).

 

E is a double slip.

 

F facing points on passenger lines have to have facing point locks fitted.

 

BeRTIe

Edited January 22, 2023 by BR traction instructor

[sjp23480]

6 minutes ago, BR traction instructor said:

A is a single slip.

 

B & C are diamond crossings.

 

BeRTIe

Isn't A a double slip  (same as E) and B a single slip?  C is a diamond crossing

Edited January 22, 2023 by sjp23480

[BR traction instructor]

Apologies, see above.

 

BeRTIe

[Jeremy Cumberland]

A is a double slip with one set of blades being hand worked (and, more to the point -excuse the pun - trailable).

 

The numbers refer to which switches are worked by which lever. Levers can work multiple sets of switches, such as both ends of a crossover.

 

[Jeremy Cumberland]

7 is the facing point lock for one end of 8.

8 is a crossover with one end being part of a single slip.
5 is also in effect a crossover, with one end being part of a single slip and the other end being part of a double slip.

One end of 15 appears to be a trap, but it could be a set of points. It protects the running line, either way.

18 operates four switches (2 at each end) of the double slip E. This arrangement is common. Two of the other switches are worked by 19 and two are hand-worked (the same arrangement as double slip A).

20 is a facing point lock for one end of 19.

 

Most of your questions you would be able to work out for yourself if you, for example, assemble a double slip, a single slip and a left hand point  on a bench to represent A, B and the other end of 8, and operate the switches by hand to represent operating different levers.

Looking at levers 4, 5 and 8 (and ignoring 7), with all levers normal, the following routes are set:

- top platform face to loop line

- bottom platform face to main line

- siding 1 to headshunt

- siding 2 to headshunt

 

4 and 5 are probably locked at this point, but if you pull 8, you will set the bottom platform to the loop line.

 

4 is probably still locked, but if you now pull 5, you will set the loop line to siding 1. If you now pull 4, you will set the loop line to siding 2.

[The Stationmaster]

Most of it has now been explained by a couple of things -

 

The symbols used on signalling drawing  are shown in British Standard (BS) 376 part 1.   It has been revised and updated over the years to drop older symbols no longer needed and bring in new symbols.

 

7, 14, and 20 are drawn using the standard symbol for a facing point locki(ing) bar and that bar in turn works the facing point lock (the little symbol show going into the switch toe).  The purpose of the lock(ing) bar was to prevent points being unlocked as passenger train was passing over it as it was held in the down (locked) position by the wheel (the flanges of the wheels in this case) of the passing trains.  

Lock(ing) bars were gradually displaced by the use of track circuits leaving so on a drawing like this only that facing point lock symbol would be used and the short line parallel to the line representing the track wouldn't be there.

 

The arrangement of the numbering (and therefore which lever worked which switches) in. a double slip varied.  The double slips in this location had separate stretcher bars for the two switches at either end of the double slip.  Later it became much more common for both switches at the same end to be connected to each other to and work together as it potentially allowed the number of levers (in the signal box) to be reduced

Similarly of course whenever possible opposing points are arranged to work as a crossover which saves a lever and simplifies the interlocking. - as with 5 and 19.

[Grovenor]

1 hour ago, Halton Boy said:

Hello Everyone

I have been all over the internet and on this site, but I cannot find the explanation I need.

Here is a typical signal box diagram:

I understand the signals like starter, home and ground disc's.

What I don't understand is what some parts of the drawing mean.

I have added letters A,B and C etc to the drawing to highlight the parts I do not understand.

Part A

Is 4 and 4 a double slip?       What is 5A and 5B? 

You have found a location with an unusual arrangement of double slips where each of the 4 sets of switches is independent, more usually the 4 switches at each end operate together. At A you have a double slip where the switches shown with a crossbar are hand operated so a shunter can select either siding from the headshunt without needing any box levers pulled. Signal 3 applies to both sidings for routes across the running line into the loop. To pull signal 3  for a move from the upper of the two sidings you must fist pull 8 which sets the crossover beween running line and loop, then 5 which sets the two point ends out of the sidings, one on the double slip and one on the single slip at B, then you can pull 3.

To make the move from the lower siding will need 8, 5 and 4 pulled then 3. The more conventional arrangement of double slip would be better as lever 4 would not be needed and there would be less chance of a un through if the signalman forgot to pull 4.

Part B

Is 7 a facing point lever?  7 is a facing point lock lever with lockbar (the line parallel to the track)   

  What is 8 and 8 is this a cross over?  yes.

What is 5B It looks like single slip if there is such a thing. Single slips are common and this is one, one end of the slip is operated by lever 8, the other end by lever 5.

Part C

Is this like a Peco 8 deg crossing?  It is a diamond crosssing between the two sidings, you would need a scale plan to determine the angle.

Part D

Is 14 a facing point lever?  Facing point lock lever, as for 7 and 20.

Is 15 a point linked to a trap point 15 before the engine shed to protect the running line? Yes

Part E

Is 18 and 18 a double slip?   Is 19 and 19 the cross over? How do these relate to each other, please.

See answer to A, this is a similar arrangement.

Part F

Is 20 a facing point lever. Facing point lock lever, as for 7 and 14.

 

I have reproduced the drawing in Anyrail below:

A,B and E are all double slips in Anyrail. 15b is a left hand trap point.

B should be a single slip, not a double slip.

 

If A,B and E are double slips why is the drawing marked with 5-5 and 8 - 8. Why 18 -18 and 19-19?

See answers above.

8 is a LH point, is 8 on the double slip a form of interlocking? See above 8 and 8 are a crossover and so work together, it does form part of the interlocking as the upper point worked by 8 forms a trap to protect the running line when 8 is set normal as in the diagram.

19 is a RH point, is 19 on the double slip a form of interlocking? As for 8 above..

Are the double slip at A and at B interlocked by 5 and 5? Explained in firs answer to A.

How would an engine run from the head shunt at Engine start to the siding at engine finish? 

From the headshunt at 'engine start' the shunter will set the 3 sets of hand points and wave the driver to proceed to signal 9. the signalman will then pull 8, 5 and 4 to set the route and then lever 9 that will clear signal 9 and lock the point levers in position. Driver then proceeds in accordance with the signal.

Is this why there is 18 -18 and 19 -19, 8 - 8 and 5, 4 - 4 and 5 at the double slips?  It is standard practice to operate both ends of a crossover from one lever, which explains 5, 8 and 19.  4 and 18 are required because of the unusual arrangements for operating the double slips as in answer to A.

I am sorry this is such a lot to answer, but I am stumped, you are my only hope.

Thank you for your help.

 

I have added my answers to your text, hence you need to 'expand' to see them.

Edited January 22, 2023 by Grovenor

[Grovenor]

Given that the BS 376 costs a ludicrous amount and BSI are very protective of their copyright you may find this helpful. https://dickthesignals.co.uk/onewebmedia/4 introduction to plan symbols.pdf

[Halton Boy]

Hello everyone

Thank you for your help. Thank you Grovenor for the PDF, I will read through that again.

I think I understand the signal box plan now. I liked the plan because it was unusual, but it's expensive to build.

I have another plan which has some things I am not sure about:

 

Part A

Is this a RH point operated by the fireman from the ground frame?

Part B

Is this a trap point linked to point A, to protect the main line?

Part C

What is this please? Is it a king lever which releases the ground frame from the signal box?

Part D

What does W:10  S:0 and T:10 mean?

Part E   (should be in red)

Is this a trap point linked to point 4, to protect the main line?

Part F

9a 9b 9c ,

Is 9a a RH point?

Is 9b and 9c a single slip? 

I now understand what the parallel lines are by the FPL's 

Thank you all for your help.

 

[Jeremy Cumberland]

Replying to the new plan.

 

A and B will both be worked off the same lever of the ground frame. B is a trap to protect the running line.

 

C appears to be a token instrument. There is something odd about the shape, though, which I don't recognise but I am sure someone will explain. The ground frame is released by lever 1 in the signalbox.

 

D: W=Working. S=Spare. T=Total (levers)

 

E. Yes, it's a trap to protect the running line. Both the points and the trap are worked by lever 4.

 

F is a hand worked point. I don't think it is possible to say from the diagram what hand it is (it could be a Y). I suggest you try to find a photograph or 1:2500 (25") map of the location.

9a is a right hand point.

9b and 9c are traps. Presumably point F is too close to the running line to fit a trap between it and 9a. Conceivably, the traps are between the crossing and the switches of the hand-worked point; since things seem to be a little cramped in this area.

Note signal 8 applies to both the goods shed line and the down sidings.

[Grovenor]

I agree with Jeremy.

9a and 9b are traps, nothing to do with a single slip. Its possible if they are double tongued traps that they could look like the blades of a double slip, but more commonly they would be single tongued traps. A similar installation can be seen in photos of the pre-preservation Bodmin General among other places.

Edited January 22, 2023 by Grovenor

[Halton Boy]

Hello everyone

Here is the plan in Anyrail:

I have used two points for 9b and 9c.

I could put a trap point between 9a and 9b which would help with the space for the station platform.

When the engine leaves the goods shed;   6 is pulled, 9a is pulled, 9b is pulled and 8 is pulled. The engine continues on the main line.

When the engine leaves the down siding;  6 is pulled, 9a is pulled, 9b is normal, 9c is normal and 8 is pulled. The engine continues on the main line.

I wonder why the loop is called a loop siding and not a run round loop?

 

Thank you Jeremy and Keith for your help.

Everything is much clearer now.

 

[Jeremy Cumberland]

I think you misunderstand how some of this works. There is only one lever 9. It operates one set of points and two traps. What you have labelled 9b abd 9c are hand-worked points.

 

If you want to replicate this in AnyRail (which I have not used, so I am not quite sure what is available), I think the best way would be to keep 9a as is, and connect to the diverging line either a right hand or a Y point, most likely with no intervening plain track. This is the first hand-worked point. Immediately beyond this on both branches, fit a left-hand trap or catch. These are 9b and 9c. On the right hand branch, fit a left hand point. This is the second hand-worked point, leading to the down sidings.

 

For an engine leaving the goods shed, assuming FPLs stand unlocked (normal position of the lever in the frame = points unlocked), then the signaller will pull 9 then 8. If FPLs stand locked, then the signaller will need to pull 6 first. For an engine leaving the down sidings, the signaller pulls exactly the same levers, since the only difference between the goods shed line and the down sidings for getting on or off the main line is the position of the hand-worked point.

[Harlequin]

The diagram seems to indicate that 9b and 9c are worked from the 'box.

 

I suspect that we are missing some information about this diagram and how 9b and 9c are arranged so that only one or the other can be "worked" at any given time because it seems odd to be able to set up potentially conflicting movements.

 

Edited January 23, 2023 by Harlequin

[Jeremy Cumberland]

It might look something like this:

 

I can't make single switch traps in Diesel Railcar Simulator. There is nothing in the diagram to say exactly what form or exactly where the traps are.

 

The point right at the top is 9. The one just visible on the right is 4 (not quite in the right place, I think). The one in the middle and the one just visible bottom left are hand worked. Both traps are worked off lever 9.

 

Edit: In answer to @Harlequin both traps are worked together, at the same time as points 9. The signaller sets the road for the goods shed/down sidings, and doesn't care which road the vehicles come from/go to.

 

Edited January 22, 2023 by Jeremy C

[Michael Hodgson]

I don't think anybody has explained No 1 lever.  One of the conventions is that lever numbers are shown against the equipment they work.  But that doesn't really work for some types of lever, so a few oddities like releases, spare levers, king levers , etc are simply explained in text in an otherwise area of blank space on the drawing.  No. 1 is a lever (in the signal box) which the signalman has to pull before the train crew can operate any of the levers in the ground frame, because the ground frame is normally locked with the line set to the platform.  As drawn, we can see it's a 2-lever ground frame.  Another detail we can see from the diagram is the position of the frame in the signal box - it's along the front (represented by the line) and the signalman stands behind it (represented by the dot). If the frame were along the back wall of the box, the dot would be above the line - and the lever numbers would typically run in the reverse order.

 

The little table at the bottom left has been explained above, and it is useful as it allows us to reconcile the number of levers in the frame to the diagram to ensure that everything has been drawn.  Not always shown, some diagrams don't have it.  Note that there is no number against the Up Distant - that's because it is fixed at caution, indicated as such by the line drawn along the middle of the arm.

 

You questioned whether C was a King lever to release the ground frame - a King lever is a lever in the signalbox which rearranges the locking - usually for signalboxes which can switch out of circuit, so that the signalman can clear signals in opposing directions on a single line when the closes for the night.  The key token instrument at C ins unusually placed - normally it would be in the signalbox (and not shown on the diagram), and I don't see the reason it's where it is.  There are situations where an extra (intermediate or auxiliary) instrument would be provided to be worked by train crew, but this is usually because there is either no signalbox or the box is very inconveniently located for issue or collection of the token.  That's not an issue here as every arriving or departing train passes the box.  At some Scottish stations however the instrument would be in the station building as control of tokens was the Station Master's job rather than a signalman.

 

The way points are drawn shows the way they lie when all levers are normal in the frame.  The route not set is shown not quite touching the line it joins.  If the converging routes at a point are drawn touching, the box doesn't control their lie - as at a hand point; the short right angled line at the toe of the point signifies hand operation.  The same of course applies to slips, which may help you understand diagrams showing slips.  Where levers control more than one set of blades, the number is shown against each such set of blades - so lever 9 moves point 9a and traps 9b and 9c and it doesn't matter which way the hand point between them lies.  It's the responsibiity of the loco crew/shunter to make sure the hand points are set correctly for movements.

 

 

[Halton Boy]

Hello Michael

Thank you for your advice.

The plan is for a North British Scottish station as your said. The station is called Penicuik.

I did not know that it would make a difference to the placement of the token instrument.

All the levers in the signal box frame are used. Therefore I have put lever 1 as a brown lever controlling the ground frame.

I am not sure about the colour, but that is all I can find online. I know the colour would change with different companies.

I was intending to change this to GWR or LMS in 1947.

 

I have marked the plan with ground frame lever No1 controlling the point to the loop siding, trap and point out of the loop siding.

I have marked the plan with ground frame lever No2 controlling the point to the up sidings.

 

With ground frame lever No1 set to normal and ground frame lever No2 set to normal an engine could shunt the top up siding to the main line.

With ground frame lever No1 set to normal (this does not affect the lower siding) and ground frame lever No2 set to the siding an engine could shunt the lower up siding to the main line.

With ground frame lever No1 set to the loop siding and ground frame lever No2 set to normal an engine could run round the loop on to the main.

Would the distance from the ground frame to the up siding points cause a problem with the driver and fireman communicating with each other or with a shunter, depending who is working the ground frame.

 

What would the token machine in the station masters office be used for?

Was it the token for single line running?

 

I think I have got most things right now?

Thank you for your help every one.

I will continue my search for interesting branch line stations. I may find one that has not been modelled!

 

 

 

[The Stationmaster]

14 hours ago, Harlequin said:

The diagram seems to indicate that 9b and 9c are worked from the 'box.

 

I suspect that we are missing some information about this diagram and how 9b and 9c are arranged so that only one or the other can be "worked" at any given time because it seems odd to be able to set up potentially conflicting movements.

 

9b and 9c are probably arranged like this as single tongue traps - quite a common arrangement where space was tight and maximum sfding length was needed plus it was simpler to connect up to the rodding run than a separate trap further back on each siding...

 

 

Alternatively  - although very unlikely at that sort of location they could have been what amounted to half (i.e one end) of a doube slip but these were normally only found in mot re complex yards when space was tight (I have a photo of one if anybody is interested but it's a modern replacement using flat bottom rail)

[Harlequin]

15 minutes ago, The Stationmaster said:

9b and 9c are probably arranged like this as single tongue traps - quite a common arrangement where space was tight and maximum sfding length was needed plus it was simpler to connect up to the rodding run than a separate trap further back on each siding...

 

 

Alternatively  - although very unlikely at that sort of location they could have been what amounted to half (i.e one end) of a doube slip but these were normally only found in mot re complex yards when space was tight (I have a photo of one if anybody is interested but it's a modern replacement using flat bottom rail)

 

I see. So those two traps are in fact equivalent to one after the hand-worked points but because there's no room for a trap there it has to be moved further back, after the track has diverged, and thus becomes two worked from the same lever.

 

You learn something new every day!

 

[Michael Hodgson]

Release levers are usually painted brown.  Different companies did use different lever colour conventions, but there was a great of similarity between them asregards main colour, and the differences tended to be on more obscure equipment anyway like gongs, king levers or bolt locking between two boxes.  The variations tended to be bands of additional colours to indicate something such as goods/releief line.  The main change of any significance was distant levers changed from green to yellow about the same time distant arms chaned from red to yellow (1920s) - except in Ireland.

 

Modellers run into an issue with lever frames in that we tend to motorise points which on the prototype were  hand worked so we need a lever to control them.  On the other hand facing point locks are rarely modelled as such, so there may be some spare levers although usual modeller practice is to save money/work by not installing spare levers.

Where the modeller chooses to use a lever frame as his control system, he therefore can't follow the prototype.  I've seen various solutions to this - sometimes an extra (non-prototypical) ground frame is provided, either separately or at one end of the frame.  Their levers may be

painted in an odd colour - examples I've seen include white (for spare on the prototype), green (usually gongs), purple or orange (I've never seen used by prototype) or grey  which I've only come across in a special scheme for fog. 

[Michael Hodgson]

8 minutes ago, Harlequin said:

 

I see. So those two traps are in fact equivalent to one after the hand-worked points but because there's no room for a trap there it has to be moved further back, after the track has diverged, and thus becomes two worked from the same lever.

 

Yes.  The purpose of the trap is to protect the main line - except when you need to come out/go into the yard.  You don't bother to protect one siding against another, so it's OK to have the trap opened for the siding you're not coming out of at the same time as the one you are using, and the cheapest approach is to put the whole lot on the one lever.

[Grovenor]

Halton Boy said,

Quote

 

Ihave marked the plan with ground frame lever No1 controlling the point to the loop siding, trap and point out of the loop siding.

I have marked the plan with ground frame lever No2 controlling the point to the up sidings.

 

With ground frame lever No1 set to normal and ground frame lever No2 set to normal an engine could shunt the top up siding to the main line.

With ground frame lever No1 set to normal (this does not affect the lower siding) and ground frame lever No2 set to the siding an engine could shunt the lower up siding to the main line.

With ground frame lever No1 set to the loop siding and ground frame lever No2 set to normal an engine could run round the loop on to the main.

Would the distance from the ground frame to the up siding points cause a problem with the driver and fireman communicating with each other or with a shunter, depending who is working the ground frame.

 

The ground frame would only control the platform line point and its trap that you have labelled 1a and 1b. The other points in the up sidings would be hand points with levers adjacent to each point. The ground frame is only there to provide for 1a and 1b to be interlocked with the signal box. Lever 1 in the signalbox, when pulled energises an electric lock on lever 1 in the ground frame allowing that lever to be pulled. While the ground frame lever 1 is reverse the signalbox lever 1 will be locked, by another electric lock, in the reverse position and that will prevent the home or starter signals being cleared. The ground frame lever 1 reverse will release ground frame lever 2 which will actually operate the point and trap.
 

Quote

 

What would the token machine in the station masters office be used for?

Was it the token for single line running?

 

Yes.

Edited January 23, 2023 by Grovenor

[Jeremy Cumberland]

3 hours ago, The Stationmaster said:

9b and 9c are probably arranged like this as single tongue traps - quite a common arrangement where space was tight and maximum sfding length was needed plus it was simpler to connect up to the rodding run than a separate trap further back on each siding...

 

 

Alternatively  - although very unlikely at that sort of location they could have been what amounted to half (i.e one end) of a doube slip but these were normally only found in mot re complex yards when space was tight (I have a photo of one if anybody is interested but it's a modern replacement using flat bottom rail)

I was looking for a picture like that one!

 

@Halton Boy are you intending to have working interlocking between levers?

For a model, you may as well use lever 1 for the run round points and trap. The prototype only has a separate ground frame to avoid the need for signals and so the person operating the levers can see what the engine is doing (and vice versa, in the absence of signals).

 

This leaves the four hand-worked points which, if you want a prototypical feel, can be controlled entirely separately (individual levers in line with the actual points, perhaps). Michael offers a number of good suggestions.

 

Personally, I wouldn't be inclined to include the loop siding point on 1 (or GF1) as this restricts how you might use the loop. You would not, for example, be able to bring a goods train into the loop siding and run round it if the back of the train was foul of the loop siding points.

 

4 hours ago, Halton Boy said:

Would the distance from the ground frame to the up siding points cause a problem with the driver and fireman communicating with each other or with a shunter, depending who is working the ground frame.

Yes, and the whole idea seems bizarre. In a busy goods yard a ground frame might control points some distance away, and have signals too, so the person operating the ground frame can let the driver know the route has been set, but you wouldn't get this at a branch line terminus.

 

The four hand-worked points at this station would have been operated by levers immediately adjacent to each point.

 

[Grovenor]

Quote

Personally, I wouldn't be inclined to include the loop siding point on 1 (or GF1) as this restricts how you might use the loop.

Both you and I have clearly said that the GF would only controthe run round points and trap so this is not an issue.l

 

Quote

You would not, for example, be able to bring a goods train into the loop siding and run round it if the back of the train was foul of the loop siding points.

The usual operation at such a station would be for the goods to arrive in the platform, run round, then shunt from there.