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Semaphore Signalling and Modelling !

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  • Semaphore Signalling and Modelling !

    CONGRATULATIONS TO DAPOL.
    Finally after Decades of British outline models in OO & N gauge, a major player (DAPOL) has finally taken the plunge into the complex realms of semaphore signalling. Having produced an expanding range of quality and well detailed, electrically operational, ready made working examples.

    Indeed this range has come just in time for my new and rather large exhibition layout. My "OO" scale layout "Basingstoke 1958-67" will be, when complete, 85 feet x 23 feet. It will not only feature the busy four track mainline junction of Basingstoke station but also Hook station (one stop nearer London), Oakley station to the south and the first stop on the Salisbury line, as well as part of the Basingstoke to Reading line. It will need approximately 100 signals !

    The layout is currently under construction at the MORA LA NOVA , RAILWAY MUSEUM & RAILWAY CENTRE near TARRAGONA in SPAIN. Hundreds of photos of the layouts progress are already available to see on "RMweb", in the category "MODELLING REAL LOCATIONS" under the title "BASINGSTOKE IN OO 1958-67". Although i haven't reached the stage of adding signalling yet, it will soon reveal DAPOL signals working exactly as their real life counterparts did, with the added aid of TRACK CIRCUITS !

    As an ex BR Driver, with experience driving trains ALL over the World, I know quite a lot about the various signalling systems used. This knowledge is very helpful when building layouts, so I am a very happy customer of DAPOL's new range of semaphore signals. As they will aid me considerably in speeding up completion of this current massive project.

    Signalling however is understood to be a minefield for those modellers who haven't been Train Drivers or Signalmen. Indeed the following may also be of use to DAPOL staff considering their next signal products to add to the range !!!

    The first rule of signalling which must be carefully considered states "Signalling is for the SAFE REGULATION of trains". It means basically that NO train or locomotive can move, without the Signalmans authority first, through the use of some sort of signal indication.

    ABSOLUTE BLOCK (The most common system used with semaphores)
    The problem of trains is that unlike cars they have a big problem stopping once you have got them in motion. In Steam days with unfitted freight trains (i.e wagons with nothing but a handbrake) this presented very big safety problems, and so semaphore signalling had to be designed to take into consideration this "worse case scenario". On the average two track railway a system known as "ABSOLUTE BLOCK" was used to safely regulate the flow of trains. The fundamental rule of the Absolute Block system, states that: only ONE train can be present on each track controlled by a Signalbox. Regradless of how many signals the box controlled on each line. Trains were NOT therefore allowed to follow each other from signal to signal as with more modern forms of signalling. But only from Signalbox area to Signalbox area.

    Not adhering to this basic rule, resulted in Britains worst ever train crash at Quintinshill on the Scottish border north of Carlisle. Where in excess of 256 persons died in a ghastly Four train pile up. And all because a train Guard forgot to ensure the signalman placed a "reminder device" on the signal lever controlling the signal that was protecting his stationary train. Held up at Quintinshill by operational delays, around the year 1900. The box it should be noted was also found in the subsequent investigation to be lacking in full interlocking. You can read the detail of this and other nasty disasters, in the famous paperback "Red for Danger" published by Pan books.

    Therefore the basic method of semaphore signalling was laid out as follows. Signalboxes were normally provided at Stations, Junctions, and possibly other helpful locations. As semaphore signals were normally mechanically operated by a wire. This set a maximum wire length, due to expansion and contraction of the wire, to just over a mile. So a mechanical signalbox could basically cover a maximum distance of two miles of line (one mile each side of the box). Between these controlled areas were sections of line known basically as "No Mans Land", as there were NO signals. Points it must be added, were controlled by rods, and as these also expanded and contracted, they limited the distance of points to just 660 yards from the box controlling them. Hence the need for more than one signalbox at larger stations such as Basingstoke.

    So a train driver approaching an area of semaphore signalling would first encounter a "Distant" signal. Post 1923 Distant arms have always been painted yellow with a fishtail "V" cut out of the end. The Distant signal is VERY important, although you never have to stop at it. What it tells the Driver, is that if the signal is at Caution he MUST be prepared to Stop at ONE OR MORE of the following STOP signals controlled by that signalbox. The Driver MUST therefore assume that the first stop signal he sees MAY be at danger, and bring his train under control in preperation to stop.

    If the DISTANT signal is showing clear, this means ALL the stop signals controlled by the box ahead are also CLEAR and the driver has a clear line right through the area covered by this signalbox. The distance between the DISTANT signal and the First stop signal is therefore critical, to the braking ability of any train.

    This explanation of the semaphore Distant signal, also reveals why Colour light signals can NOT be called Distant signals, unless they are being used as a (two aspect yellow/green) semaphore substitute, as in the case of an "Intermediate Block" in an "Absolute Block" area.

    Having passed the Distant signal the first stop signal encountered is a HOME signal, and this signal is before the box is reached. The first signal AFTER passing the signalbox, is called a STARTER. So the minimum number of signals controlled on each line by the box is 3: Distant, Home and Starter, in that order. However many stations had pointwork often at either end of the actual station. This often resulted where necessary in the addition of more stop signals. If pointwork existed just prior to the station it was common to have two HOME signals before the box is reached. To avoid confusion the one furthest from the box, and the one first encountered by the driver was known as the OUTER HOME. The term INNER HOME could be used for the one closer to the box, or just HOME. Depending on the Region, thanks to the complexity of railway History.

    In the same way pointwork at the far end of the station would require a Starter on the platform end, then the pointwork, and an ADVANCED STARTER probably about a train length or so further on. It must be added here, as this is important for modellers, that the only critical distance between semaphore signals operating under ABSOLUTE BLOCK rules, is the distance between the Distant and the first STOP signal. The distance between the various Stop signals is not important, and they can be less than a trains length apart, or more, as the location requires and permits by available space.

    Whatever signals are provided for any particular signalbox, which is also known as a "BLOCK POST". It must also be explained that the last stop signal before the train moves out into "No Mans Land" is also known as the "BLOCK" signal, although rarely referred to as such. The "BLOCK" signal is the last place a signalman can stop a train in the case of a problem. It is also the signal that the signalman CANNOT pull to clear. That is until the signalbox ahead, along the line, gives him an electrical release, to allow it to be pulled to clear. This is because only ONE train can be on each line controlled by the signalbox. So the next box up the line must have a "CLEAR" line before he can acept another train. The Signalman must therefore have some control over the previous boxes "Block"signal, to prevent the previous box, from sending another train. Hence the requirement for the signalman to ask the next box for permission to release his own "BLOCK" signal. Which complies with the fundamental "ABSOLUTE BLOCK" rule of ONE train per line per signalbox area.

    The "Intermediate Block" is a term relating to a situation where a long gap between signalboxes was leading to trains being delayed. Most likely as a result of an increased demand for more trains. The solution to this problem was normally to provide another signalbox and signals to break up a long gap. However by the 1920's the availability of electricity, even from batteries, was now reliable enough to introduce a cheaper alternative than another signalbox. The "gap" could now be plugged, by providing a Distant and a Stop signal controlled by electric motors and controlled from the signalbox in "advance". The signals were in that age semaphores, but colour light sempahore substitute signals became an even cheaper option from the mid 1930's. As these "Intermediate Block" signals could only be controlled by a signalbox in advance. This means that on a two track line, the sigtnals on each track (one Up line and one Down line) would be controlled by the boxes either side of this "Intermediate block". As "Intermediate Block" signals, the original rules were that if a train was held at the stop signal for more than eight minutes. The driver could sound the horn and pass the signal at danger (telephones being rare at this time) and proceed gently at caution towards the next signalbox. The "Intermediate Block" was regarded as such (Intermediate) on an otherwise Absolute Block line. The only one I can think of, off hand, was at Riddlesdown on the line from Croydon to Oxted (in Surrey), and was in existence until this line was electrified and resignalled back in the 1980's. The Up Intermediates signals were controlled by Sanderstead box, and the Down Intermediate signals by Upper Warlingham box. They were of a very old style of two aspect colour light semaphore substitute, with just a green/yellow distant followed by a red/green stop signal.

    "Electric Token Block" (single lines)
    Single track lines with passing loops used a modified version of the ABSOLUTE BLOCK system which added another safety feature known as the Token. Which had to be given to the driver before he entered a single line. Most of these single lines used what was known as the "ELECTRIC TOKEN BLOCK" system. Which needed electrically worked "token machines" in each box at both ends of a single line section. This all being in addition to the regular postioning of Distant, Home and Starter signals.

    "Permissive Block". (A long dead system !)
    Another complex oddity was known as "Permissive Block". This must not be confused with "Permissive Working" as they are totally different. Permissive Block was fairly rare, but was used on the old MIDLAND mainline, and areas where there was a lot of freight. It was also correctly modelled many years ago on "The Model Railway Club's" layout in 2mm finescale called "Chiltern Green". The principle goes like this. A section of line can change from "ABSOLUTE BLOCK" working to "PERMISSIVE BLOCK" working only after the last passenger train has left the "BLOCK", and can ONLY be used for freight and light locomotives. The signalboxes in question must also have certain extra equipment that can allow signals to be pulled to clear, when NOT possible due to the interlocking under Absolute Block rules. Once Permissive Block working begins, freight trains and or light locomotives are allowed to follow each other at 25mph on the proviso they keep at least 250yds apart. (Very hairy in thick smog !) All the signals are normally left at clear until the last signalbox using the system is reached. Here the stop signals will be in use, and each train will be let out into the normal Absolute Block system under the normal guidance of the signals. This system was therefore only used during times of freight only operation, and as far as I'm aware this system disappeared by the late 1960's, along with steam.

    Station Permissive Working (and Calling on signals).
    "Permissive Working" is normally used within station areas, to allow for the provision of having two seperate passenger trains couple together, or divide in a station platform. Which obviously breaks the fundamental rule of having two trains in one Absolute Block area, or even two trains between signals on the modern "Track Circuit Block" system used with modern colour light signalling. In both semaphore and colour light areas, the use of Permissive Block in station areas, requires the addition of "Subsiduary signals". On semaphore signalled lines, a signalbox using the "Absolute Block system" can accept a second train into his area (from the previous box), because his signalling has been provided with "Calling on" signals. These are most commonly smaller than normal semaphore arms. These "Calling on" arms are positioned below the main signal for the line to which they refer. The second train must be brought to a halt at the Home signal before the station. Only when the signalman is happy the train is stationary should he pull the subsiduary "Calling on" arm to clear. The main arm is locked at danger by the presence of a train in the platform. So the second train and its Driver are aware that they must pass the main signal at DANGER, and under the provision of the Calling on arm: "Proceed at caution and be prepared to stop short of any obstruction, and not assume the position of the train in the platform ahead". The driver was also to bring his train to a halt at least 15ft before the train he was to couple too, and await handsignals before actually coupling up.

    Track Circuit Block.
    This is a system needed for modern (colour light signalling). It came about due to the demand to move lots of trains at closer intervals than the Absolute Block system could allow. It fundamentally changed working arrangements by requiring continuos track circuits in the rails, which could detect a trains presence, and automatically turn signals back to danger as soon as a train passed them, without a signalman being required to do this. It could in addition allow signals to be fully automatic but it was NOT the system that introduced automatic signals. To work safely this system can only be used with signals that can show STOP, CAUTION and Line CLEAR, and in most cases this means a minimum of 3 aspect colour lights. Its first major installation (after certain tests) was in conjunction with the London to Brighton third rail electrification by the Southern Railway in 1933. It allowed headways between trains to be reduced to as little as 150 seconds (with the aid of four aspect signals)!

    SEMAPHORE SIGNAL TYPES
    The Distant as mentioned is normally a 4ft or 5ft length arm, painted yellow (post 1923) with a fishtail "V" cut out of its end, and a black chevron about a foot inboard from the cut out end.

    A normal Stop signal is again usually a 4 or 5ft long arm painted red, with a white vertical stripe about a foot inboard from its outer end.

    A "Reversing signal" A Great Western love affair ! The reversing signal was normally a 3ft arm painted red with two holes in it. They were positioned often on their own signal post, to allow locomotives to make wrong line reversing movements normally within station limits. They weren't soley confined to the GWR but rare on other railways who often just used little ground level shunting signals.

    "Freight signals". Most commonly a 3 or 4ft arm painted red with a white ring attached to the outer end, although colours did vary slightly. Only freight or light locomotives could accept these signals, and they were normally positioned on their own posts, at the entrance or exit from freight only lines, loops, or sidings.

    A "Calling on" signal can come in a number of slightly different varieties dependant on which Railway company originally installed it. However probably the most typical type, is a 2 or 3ft arm, with a red white red horizontal banding the length of the arm. As its name implies, it was provided beneath a main stop signal to allow entry into an already occupied platform, under caution.

    "Banner Repeater". This is a circular white box (illuminated) with a black bar. The bar can move between the horizontal and 45 degrees. A rare Distant version had a fishtail "V" cut out of the left hand end of the black bar. These signals give warning of the signal ahead, by repeating their indication in areas of bad sighting. The rule concerning their positioning is complex, but they must be positioned at the point where the driver passes the banner, and at the same moment comes into view of the signal that the Banner Repeater is repeating. This is critical in case the signalman or the automatic detection system makes an emergency replacement (to red) of the signal being approached. If you see a clear banner, and then discover the signal is at danger, valuable stopping distance has been lost, hence the complex system to position the banner repeater precisely.

    "Mechanical Theatre boxes". These are the precursor to modern "Theatre boxes" which can display numbers and or letters. The mechanical type was often a box, where the lower half was black, and hid the moving mechanical stencil plates. While the top half was white, and acted as a backing for the black stencil plates. Only one plate at a time, from those provided could be displayed to reveal a number, letter, or even an abbreviation, to indicate to which track a train was routed. They worked in conjunction with a stop signal, and would show nothing while the main signal above was at danger. They provided an alternative to large gantries of numerous signals at Junctions. But where normally only provided when there was a problem of limited space, and or sighting. Such as inside the old GWR Snow Hill station at Birmingham.

    A "Shunt ahead" signal again came in various slightly different forms, but the most typical is a signal arm of 3 to 5ft in length with a "S" letter screwed to it. The arm is red, and the "S" white. It was positioned beneath the "Block" signal. They were not common, and were required on the odd ocassions where a freight train needed to pass the "Block" signal solely for the purpose of shunting into sidings a limited distance ahead of the Block signal,

    "Warning" arrangement signal. Again a 3 to 5ft arm painted red, with a "W" screwed to it painted white. It was positioned below a normal stop signal. Very rare post WW2. It was needed for a complex reason involving a fouling of the "overlap" by possibly a level crossing ahead of the NEXT stop signal. Beyond each stop signal was a 220 yd "overlap" or safety zone. If this was obstructed for any reason such as a level crossing, a train was NOT allowed to approach this stop signal and had to be stopped at the previous stop signal. So a level crossing for example just ahead of the platform starter, presents a problem. The crossing would have to be closed before a train could enter the station and stop. This drives the road users potty, as no train passes, and the gates suddenly open again. So to avoid this problem a "Warning" signal is placed below the Home signal. When pulled to clear it tells the train Driver, you are clear to pass the Home signal at Danger, and proceed at Caution towards the next stop signal but you have NO overlap. Because in this case the level crossing gates are open for road users. Overlaps were a necessity in the days of unfitted freight and even vacuum braked steam trains. Although a few of these signals lasted into modern times. Overlaps are still provided at certain problem locations, particularly complex junctions, even with modern signalling and brakes.

    The classic "Ground" or shunting signal. The common denominator being they were usually at ground level, but many designs were apparant. Round being common, on the Southern often semi-circular, but ancient rotating red lamps not untypical of German or US railways were also around until fairly recent times. The normal colour of the disc types was white with a horizontal red stripe. They were positioned to control locomotive, ECS, and freight train movements (but NOT passenger trains) for virtually any movement not covered by a regular signal. So often found scattered around busy stations to cope with all the regular shunting moves. Don't forget EVERY train movement requires a signal.

    Signals officially include such things as speed restriction signs, which used to sensibly be provided with cut out stencils painted bright yellow. Such signs resisted the nasty modern habits of the graffitti artists, who on numerous occasions have altered the modern "road type" speed restriction boards now provided !

    The above is NOT an exhaustive list, but covers many of the most common and some rarer semaphore types.

    JUNCTION SIGNALS and the method of display.
    Lets assume we are out in the countryside and there is a three way junction ahead. The mainline goes straight on, but there is also a branch to the left, and another branch to the right. A signalbox will normally be present at the Junction. It will be a "Block Post", so will have a full compliment of signals for all directions with Distants, Home and Starter signals. The Junction signals themselves all situated on a complex gantry are the "Home" signals and should be positioned just prior to the signalbox and the Junction pointwork in virtually all cases.

    For the three way Junction the gantry should have three seperate posts on it. The centre one would most commonly be the tallest post, with a shorter post to the left and another shorter post to the right. The height of the centre post indicates NO speed reduction is necessary to continue at the given maximum line speed on the main route. The shorter posts to left and right indicate some speed reduction is necessary to turn onto either branch. On each of the three posts would be a normal semaphore stop arm of 4 or 5ft length. Only one of these signals could obviously be pulled to the clear position at any one time, as the interlocking in the box prevents the wrong signal being cleared, and only the signal for which the points are set, can be cleared.

    If one of the branches was a freight only line, then you might expect, certainly on the Western (ex GWR) the arm to be a ringed Freight only arm and most likely only 3ft in length.

    The principle being with Junction signals that you read the signals from left to right, and they relate to the track plan and the tracks as they are laid out from left to right. The Midland Railway had a habit of sometimes displaying Junction signals vertically on one post (Obviously couldn't afford pretty looking gantries). In this case the signals are read top to bottom and still read on the track plan from left to right. So in this case no clear indication of which is the main route and which the branches. Only the drivers route knowledge would tell him what was what !


    Signal posts with both Stop and Distant arms on.
    This type of signal is the most commonly confused type by both modellers and some manufacturers !!!!

    The upper Stop signal is controlled by the box nearest to its location. The lower Distant signal is controlled by the next signalbox ahead along the line. The only reason the Stop and Distant signals appear one above the other on the same post , is because the signalboxes are very closely spaced, such as at a large station. Large stations it must be remembered due to the maximum distance of 660 yds that pointwork can be located from the controlling box, are often forced to have two or more signalboxes. Each box needs a minimum of Distant, Home and Starter signals. So squeezing them all into the available space, left little choice but to include the Distant for the second box under most likely the last stop signal of the first box !!!

    The stop signal would in most cases be the Starter (and Block signal) of the box just past and quite probably just before the station itself is reached. The Distant controlled by the next signalbox most likely at the far end of the station, will relate to the Home signal, of the next box which in this scenario will be at the far end of the platform, and any subsequent stop signals controlled by that box. This reveals that Home and Starter signals do NOT relate in every case to the position of the station, but to the position of the signalboxes themselves, such as at Basingstoke, and many other larger stations. At Exeter St. David's station, the plethora of pointwork covering over a mile required three boxes through the station area. North, Middle and South boxes. So in typical GWR fashion signals in every direction of virtually every type imaginable, and lots of gantries with many arms for all the various platforms and routes. Including a freight avoiding line around the back of the engine shed. Just think how many lovely Dapol GWR signals you could put on a layout of Exeter St. Davids !

    Track Circuits
    Track Circuits are not a new invention and had become available back in the 1920's. They were initially used sparingly, and were first used to replace Mechanical Treadles. Mechanical Treadles were a simple form of mechanical device usually about 20-30ft long placed at critical and dangerous locations to detect the presence of a train. The detector would show up in the signalbox on a small round brass box as "train on line". This initially acted as a reminder to the signalman that an engine or train was standing say at a shunting signal. It was soon recognised that the electric (low voltage 20v or so) track circuit need not be limited to 20 or 30ft like its mechanical predecessor. As a result longer sections of line, but still restricted to problem areas around pointwork, signals, or exits from yards, became more common, whilst under the control of mechanical signalboxes. The first real use of what is regarded as the modern "Track Circuit" was introduced with the 1933 Southern Railway London to Brighton MAS (Multi-aspect signalling) the first major and the first mainline to use the modern 3 and 4 aspect colour light system which requires total and continuous "Track Circuits".

    Modelling the real railway as closely as possible on my exhibition layouts has always been my main aim. This means real life methods need to be used to generate the appeal to exhibition visitors. My exhibition layouts having always been based on mainlines, so need to be busy. I have found that many viewers have a limited appreciation time of something less than one minute. If no train moves in this time its usually: "Come along Johnny nothing is working on this one" and they are gone. Basingstoke has therefore been deliberately designed around a four track mainline. And busy it will be. I expect at least four trains to be moving at any one time. There being four mainline tracks the two track Reading line, three goods yards and a locomotive shed. Chaos can ensue on such large layouts, so real life safety features will help the operators avoid smash ups at Junctions, and the signalling which they will have to operate by, will all aid smooth and fluid mass movement. This will only be possible if track circuits are used in the tracks, coupled to relays which will interlock these with the signals, points, and even cut power to sections of track ahead of danger signals to prevent smash ups. None of this is possible using DCC. DCC by its nature is a very slow system, as you either have to remember ever locos chip number, and accessories (not possible with over 500 items to remember), or you then have to turn to lists. My operators simply have all features at their fingertips in the form of switches on a diagrammatic panel. They then simply move the train along the preset path they have set up, and any mistake simply stops the train before a crash, or even a derailment.

    The new Dapol semaphores have also revealed themselves to fit snuggly into my system. Although not mentioned in the instructions, I have already discovered that they will work happily on 6v DC. This smooths their behaviour, reduces the dayglow glare of the LED's to something more realistic, and avoids the "Frying" mentioned elsewhere on this web site. Using 6v DC also conveniently means they can run from the same signal supply for my handbuilt multi-aspect colour light signals on the four track section. Dapol Southern type signals will be used around Oakley station, and the GWR types around the Western part of Basingstoke station, and along the line towards Reading. Indeed I am not sure just why Dapol have chosen to complicate operation by trying to make them use an AC supply. I certainly don't like AC accessories, and mixing AC and DC items on one layout is asking for trouble !

    So even happier modelling now Dapol have provided us with this new and growing range of signals. And now you have some technical stuff about signals you can buy the correct models with confidence !!!


    The Duke 71000
    Last edited by The Duke 71000; 9 November 2017, 01:26.
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