Starter signals; why no distant?

[Loxborough]

OK, I think this may be a stupid question, but I am going to take the risk and stick my head over the parapet anyway...

 

I have been browsing through the various signalling advice threads here and I see that a fairly common feature is the starter signal at a through station with a distant on the same post. Which seems to make sense; the driver pulling away from a station will need to know the status of the next signal. So, normaly I would now be building one. However... looking at a wide range of images of LNER ECML southern section images from the immediately pre-war period, I can find no case of a distant sharing a post with a starter signal. Can anyone throw any light on why this might be; was LNER practice to "assume" a fixed distant as a train pulled away from a station? Or have I just not thought of something obvious?

 

Any guidance very gratefully received.

 

George

[Siberian Snooper]

It's all down to the distance between signal boxes. At a large station or junction the boxes may only be a few hundred yards apart, therefore the starter for one box will carry the distant for the next box. the distant is slotted with the starter so that it can't be pulled off until the starter is pulled off.

In a rural situation the boxes are further apart and therefore the distant will be on it's own post.

 

No doubt someone on here will put up a diagram to clarify the situation a bit more.

 

HTH SS

[PaulRhB]

Snoop has it correct. You only share a post if the next signal is close. On long fast sections the distant will be on its own post nearer the next stop signal. Many branch lines also don't share them on a post as they may have a 3-5 mile section to the next station and low service density so there's no need as the distant needs to be at the braking distance for the next stop signal. You'll also see quite a few places where they used a fixed distant on the approach to a station as the speeds were low so they didn't affect the timetable and eliminate maintenance apart from the lamp.

[Loxborough]

That's a great help, and makes perfect sense.

 

Thanks very much for the rapid responses.

 

Best,

 

G

[phil-b259]

OK, I think this may be a stupid question, but I am going to take the risk and stick my head over the parapet anyway...

 

I have been browsing through the various signalling advice threads here and I see that a fairly common feature is the starter signal at a through station with a distant on the same post. Which seems to make sense; the driver pulling away from a station will need to know the status of the next signal. So, normaly I would now be building one. However... looking at a wide range of images of LNER ECML southern section images from the immediately pre-war period, I can find no case of a distant sharing a post with a starter signal. Can anyone throw any light on why this might be; was LNER practice to "assume" a fixed distant as a train pulled away from a station? Or have I just not thought of something obvious?

 

Any guidance very gratefully received.

 

George

Please remember the principles of mechanical signalling are different from colour lights.

 

A semaphore distant signal usually applies TO MORE THAN ONE stop signal. In official terms a semaphore distant signal, when in the clear (or 'off') position tells the driver that ALL the forthcoming stop signals controlled by a single signal box (which could be anything from 2 to say 6) are also showing clear (or 'off'). If the distant signal is showing caution ('on') the the driver must expect to find at least one of the upcoming stop signals at danger ('on'). It might not be the first one or even the second one but the third one which is the culprit.

 

Sometimes in complex areas additional distant signals worked from the same box were installed but again the number of stop signals to which they applied was variable.

 

Also as has been pointed out if boxes were close together the distant for one box could end up being mounted with the last stop signal of the previous box.

 

Multiple aspect colour light signalling on the other hand has a totally different philosophy which means that when a driver encounters a cautionary (yellow) aspect he knows that the next signal he encounters will be at red.

[phil-b259]

The BR 1950 rule book states in Rule 39.(a):"When a stop a stop signal is at Danger the stop signal next in rear of it and worked from the same signal box must not be lowered for an approaching train until the train is close to such signal and has been brought quite or nearly, to a stand."So having passed a distant on, the driver would expect the next stop signal (the home) to be on as well, even if it was the inner home,starter or advanced starter etc that had to be held on for train regulation reasons. If he saw the home off after passing the distant on, then all the stop signals controlled by that box for the relevant route must be off as acceptance would now have been received from the box in advance.My GWR and SR rule books show the same rule.

Indeed and in most cases this was true, however there were plenty of locations around the country (usually around big stations) where some signals were exempt from this rule.- sometimes only under certain conditions such as the train being due to terminate. The details, conditions and signal identities concerned would be defined in the 'local instructions' of the signal box controlling said signals.

 

What I was getting at though is a pretty fundamental difference between the thinking behind the two signalling methods - on a colour light installation a yellow aspect physically garuntees signal ahead will be at danger - the control circuitry prevents the signal ahead being green in such a situation. In mechanically signalling this is not the case (unless additional controls have been fitted) and the signalman could in theory set some (or all of his stop signals) to 'off' while maintaining the distant at caution even if such an action contravenes rule 39a

[PaulRhB]

Phil there's no difference between colour light and semaphore in principle.

A distant in the horizontal position is caution expect the next signal to be stop. A distant in the upper position or lower (egGWR) is off, expect a proceed on the main aspect, and just like a colour light distant showing green. There's no real difference. You can get a yellow on a colour light distant followed by a step up to green on the main aspect if it's fitted with approach control. All it is is a timer vice the Signalman having to do it.

[PaulRhB]

- on a colour light installation a yellow aspect physically garuntees signal ahead will be at danger - the control circuitry prevents the signal ahead being green in such a situation. a

And would prevent the distant being pulled off in a semaphore installation too unless no locking tray.

 

In mechanically signalling this is not the case (unless additional controls have been fitted) and the signalman could in theory set some (or all of his stop signals) to 'off' while maintaining the distant at caution

Hopefully only one at a time or you'd be offering multiple routes. The same can be done on colour light to slow a train down by either the approach control, where there are short overlaps or speed restrictions, or if you are regulating a train doing it's manually by waiting for the train to pass the distant before clearing the main aspect. We use this to slow trains down to keep heavy freight rolling rather than coming to a stand if they are in short sections following a train that's in a long section ahead.

[phil-b259]

Phil there's no difference between colour light and semaphore in principle.A distant in the horizontal position is caution expect the next signal to be stop. A distant in the upper position or lower (egGWR) is off, expect a proceed on the main aspect, and just like a colour light distant showing green. There's no real difference. You can get a yellow on a colour light distant followed by a step up to green on the main aspect if it's fitted with approach control. All it is is a timer vice the Signalman having to do it.

When it comes to a comparison of semaphore distant sand colour light signalled areas there is a significant difference - examine the wiring diagrams / mechanical locking and they are different in principle. Semaphore signalling as designed to semaphore signalling principles does not prevent a signalman leaving his distant signal at caution if all the stop signals to which it pertains to is clear (such things are governed by the application of "rules" not design primciples) and moreover it actively enforces the requirement that unless all stop signals are showing clear the distant cannot be cleared.

 

In multiple aspect colour light signalling the single yellow coming before the red is done completely automatically and as soon as the red signal clears up to a proceed, the one in rear will (assuming a train hasn't passed it) will change up to a green / double yellow. The signalman has absolutely no involvement in the process and if he has control of multiple signals the aspect each displays simply depends on the aspect of the one in front*, not what the 4th stop signal in the chain may be doing. In places such as Stafford, Stockport, etc which still have traditional lever frames this is ably demonstrated and ithe signalling principles are very differently from back in semaphore days when the all stop signals must be clear rule would be enforced for distant signals.

 

Furthermore if you take a bog standard semaphore signalled station on a double track line with one distant one home then one starting signal then the permitted (as by design requirements - not signalmans rules) can result in a yellow, green, green sequence or a yellow green red sequence being presented to trains.

 

If you take said station and apply colour light design principles (again not rules) you get the possible sequence of yellow, red, red or green, yellow, red or green, green, green.

 

As you can see from a drivers perspective the meaning of the signal indications he may see can vary considerably between the two systems. Although in theory the correct application of the "rules" means he should never be presented with the yellow, green, red sequence, the fact that remains according to the fundamental design principles such an outcome is entirely possible wher as it cannot happen in a layout designed according to colour light principles.

 

* I'm ignoring things like approach control here because it is incorrect to say such a technique is unique to colour lights. The application of approach control in semaphore signalled areas has been, and still is applied by the simple conversion of the arm to being motor worked and the application of a track circuit timer - It doesn't change the fact that the underlying principles of semaphore and colour light MAS installations are different.

[phil-b259]

Hopefully only one at a time or you'd be offering multiple routes.

My statement referred to all stop signals in the relevant route the train I scheduled to take of course - not all stop signals in the box!

[phil-b259]

And would prevent the distant being pulled off in a semaphore installation too unless no locking tray.

You are missing the point, yes the distant might be at caution but under mechanical semaphore signalling principles, there is nothing to stop the following stop signal showing a proceed / green. Yes the signalman shouldn't let a driver see such a sequence but it remains the default design and controls to prevent such things (like approach control fitted semaphore arms were the exception not the rule).

 

In colour light signalling principles the CANNOT happen if a driver approches a caution aspect then he is garunteed that the next signal ahead will have to be at red at that time - not it simply might be at red as mechanical signalling principles allow.

[PaulRhB]

The locking principle may be different but not the operation which is what's relevant to the model. Locking may allow yellow green, red on semaphore but he ain't going to be in the job long if he's caught doing it.

I think you're confusing the issue for a model where you should see correct operation rather than what locking, rarely found on a model anyway, can allow.

The Signalmams rules have always been that if clearing a controlled stop signal on approach to another stop signal you wait until the train is at or nearly at a stand so it acts as a caution.

[PaulRhB]

Colour lights are great for dealing with the larger areas of control but they can still be used to regulate the speed of trains where you have separate track circuits between distant and stop signals. Motorised or air actuated mechanical signals can be used just like colour lights in big area installations and in other countries were used rather than going straight to multiple aspect signal heads. The colour light just has the advantage of better visiblity in poor conditions and no moving parts. With strong backlight a semaphore arm can be better than a lamp which is why LED heads are now gaining favour as they are even more intense though drivers complain about them ruining night vision. The reliability angle is yet to be substantially proved as there are a couple of issues. Circuit boards and thin tracks are more prone to corrosion failures than big wires to lamps and except in all new installations the proving circuit requires a resistor that gets very hot and has caused failure too.

[TheSignalEngineer]

There seems to be a lot of confusion here about the difference in signalling systems. From that point of view it is better to refer to Absolute Block Regulations and Track Circuit Block Regulations. It is possible to work Absolute Block with either semaphore or colour light signals, or a mixture of the two. Track Circuit Block is nowadays done with colour light signals, but in the past there were sections of line operated by automatic semaphores without block instruments, such as on the Southern main line to the West of England. On that line each automatic signal had a Home arm and Distant arm operated pneumatically. The arms were controlled by the track circuits being clear and the state of the next signal as with colour lights.

 

For an explanation of Absolute Block Working see this page and subsequent pages. http://www.signalbox.org/block/absolute01.htm

[PaulRhB]

Also some TCB sections still protected by manual semaphores, Marchwood to Totton.

[phil-b259]

The locking principle may be different but not the operation which is what's relevant to the model. Locking may allow yellow green, red on semaphore but he ain't going to be in the job long if he's caught doing it.I think you're confusing the issue for a model where you should see correct operation rather than what locking, rarely found on a model anyway, can allow.The Signalmams rules have always been that if clearing a controlled stop signal on approach to another stop signal you wait until the train is at or nearly at a stand so it acts as a caution.

Very true, as you say from a modelling perspective ultimately it is important to get things right - however there are an awful lot of modellers that assume a mechanical distant is the same as a colour light single yellow and while on the surface train movements may look similar that hides the significant difference in meaning which consequently can cause a desire to add distant signals where there shouldn't be any.

 

In reality reality the constraints most modellers are under with regards to space means that with most models a semaphore distant by virtue of its function will be well 'off scene' as it were - only the more extensive / complicated models with inner distants or those featuring a co located distant for the next box and the starting / section signal for the modelled box will have them in the viewable area.

 

With colour light MAS however (which can be combined with absolute block just as track circuit block can be used with semaphore installations), because of the requirement for every stop signal (red /green) to either have a repeater (yellow /green) or a 3 aspect head (red / yellow /green) preceding it it is more likely from a modelling perspective that you might actually see a yellow onto red sequence in the viewable area.

 

At the end of the day unless a modeller is faithfully replicating a prototype, when it comes to signalling they ARE actually undertaking the role of a signalling design engineer. Consequently if mistakes are to be avoided then some understanding of design principles is needed to ensure correct practice is followed when placing signal structures. Of course once the scheme is implemented then the modeller becomes the operator and while in the real world the operating department would have an input into the design of the signalling scheme final decisions would be the responsibility of the signalling engineers - something which modellers need to take into account.

[Dave Scott]

may I proffeer Bewdley on Severn valley Railway as an example for the original query as the station has two boxes, South and North close together. Up is towards Kidderminster.

 

An up train will first encounter North box distant followed by north home repeater and north home. This is followed by north inner home bracket which has homes over distants for p2 and p3.The inner home is north box the distant is south box. I will assume you understand slotting. The next signals are south box homes. If the north inner home is on the train will be nearly brought to a stand at the home before it is cleared. If the route into the platform is clear no caution will be made however the driver needs to be aware that if the south home is on the distant under norths inner home may be on.

 

Souths homes are before the box although they function as platform starters. The next signal encountered is the south section signal I say souths homes as there are two pairs from the days when bewdley was a junctionfon For both p3 and p2 the left home of each pair is Kidderminster and the right is Stourport but there is only one distant for each pair

 

Having writtrn this description it sounds complex but on the ground is simple. Unfortunately other than preserved railways semaphores are doomed and fast dissapearing. Old photas may be all we have. Also dont forger signal placing differed from railway to railway ane even between stations yet following the basic rules. Asimple example is GW referred to home and inner home signals. SR I believe used the terms outer and inner home for exactly the same signals 

[Eggesford box]

Hi,

 

just to pick up on one odd point. You do not have to convert a semaphore signal to motor operation to enforce approach control. Just wire the electric lock on the lever so it will not pick until a berth track circuit is occupied.Mind you that would normally be for movements onto a diverging route with a speed restriction such as a goods loop. I did not come across it on the western but I did in an ex western box that had been midlandised. Bit of a pain if you put the signal back and it did not go back fully as you could not then pull it back off, slacken the wire and slam it back into the frame to get the arm fully back on.

[TheSignalEngineer]

........................... Bit of a pain if you put the signal back and it did not go back fully as you could not then pull it back off, slacken the wire and slam it back into the frame to get the arm fully back on.

Just put the poker across the two adjacent levers to stop the lock dropping in.

[micknich2003]

Just put the poker across the two adjacent levers to stop the lock dropping in.

 

 A trick I learnt very early in my signalling carrier, but be carefull not to "Pull Off" if there are any trains about.

[The Stationmaster]

Good job I've been away for the weekend - this thread has gone through some most amazing contortions to answer a very simple question (which was of course answered very early on).

 

However I will make one point - exemptions from Rule 39(a) - as it was prior to 1972 and has which has gone through several re-namings and sundry changes since then - is not a Rule to which exemptions are granted lightly and never has been because of the dangers inherent in granting such exemptions.  

 

On the Western - where its use was very rare in later years - the only time exemptions were even considered was if a train would be approaching a stop signal slowly enough to allow it to draw to a stand at the next stop signal in advance in the event of that signal being at danger.  I can't think of any example on the Western where exemption from the Rule was granted at a stop signal immediately in advance of a worked distant signal but of course my knowledge of the Region's Signalbox Special Instructions prior to the 1980s is not complete (for the mid 1980s it is complete - I was in charge of them).

 

Getting back to the OP a feature which could be found at some larger stations where speeds were be low for through trains was the use of a single distant signal applying to the stop signals at several closely spaced signalboxes with no other distants applicable to any of them.  Thus for example - still - at Shrewsbury there are signals controlling the entrance to the section in advance at both Severn Bridge Jcn and Crew Jcn which have no lower arm distant for the 'box in advance.

[TheSignalEngineer]

Good job I've been away for the weekend ..........................

Thought it had been quiet on here.

[LNER4479]

Good job I've been away for the weekend - this thread has gone through some most amazing contortions to answer a very simple question (which was of course answered very early on).

Totally agree - I note the original poster effectively 'signed off' from the thread he started at post #4. It's no wonder there is a general perception that signalling is incomprehensible to the uninitiated... (that's not to say that subsequent posts haven't been informative or useful)