A History of Railway Signalling From The Bobby To The Balise (Stephen Clark) [PDF]

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A HISTORY OF RAILWAY SIGNALLING (from the Bobby to the Balise) Stephen Clark* *Lloyd’s Register Rail, UK 71 Fenchurch Street, London EC3M 4BS Email: [email protected]



Keywords: History, operations, technology, signalling.



Abstract The paper outlines the history of signalling from the opening of the first purpose-built passenger-carrying railway in 1830 with hand signals, through the developments of fixed lineside signals, electric telegraphs and interlocking mechanisms for points and signals. From the appearance of power signalling at the turn of the 20th century, it follows the development of first electrical and then electronic signalling technology through to present day communication-based systems.



1 Preamble The following chapters present an outline history of Railway Signalling. Although the basic principles of railway signalling and control are universal, the way in which signalling has developed in Britain differs in a number of details from practices used in Continental Europe and America. What is described here should more properly be called a ‘Brief History of British Main Line Signalling’, and covers developments in both Great Britain and Ireland.



2 Introduction



It is likely that the earliest railways existed in or about mine workings – the concept of a prepared way would have been most useful in conditions unsuitable for ordinary wagons or pack-horses, where heavy loads in quantity would have to be carried over rough ground from a mine to a road, or a canal. In Britain, the earliest record of a ‘waggonway’, using wooden rails, dates from 1630, when one was laid down near what would become the cradle of both railways and coalmining, Newcastle upon Tyne. Track using plain wooden rails quickly wore out and evolved into the ‘plateway’ with iron plates fixed to wooden bearers (track maintenance workers often used to be referred to as ‘platelayers’). Cast iron rails fastened to wooden sleepers in the now familiar pattern first appeared at the Duke of Newcastle’s Colliery near Sheffield in 1776, and the Middleton Colliery Railway, constructed to transport coal to Leeds, was the scene in 1812 of the first recorded commercial use of steam locomotives. In North-East England, the much-celebrated Stockton and Darlington Railway opened in 1825 as a freight-carrying railway, using both rope and locomotive haulage for its goods traffic, although passenger coaches pulled by horses were provided later as an afterthought.



3 Origins of the railway



In September 1830, the Duke of Wellington opened the Liverpool and Manchester Railway, the world’s first purposebuilt passenger-carrying railway with haulage by locomotives. The opening of the L&MR can therefore be considered as marking the beginning of the ‘Railway Signalling Age’, a good point at which to start a survey of signalling and its development. There is an irony in the fact that its opening is now remembered not so much as the dawn of the railway era but because there occurred during the celebrations Britain’s first public railway accident, in which the local MP, William Huskisson, was run down and severely injured by a train hauled by the ‘Rocket’, driven by George Stephenson. Despite Stephenson himself driving a special train conveying the unfortunate man to obtain medical attention, at a speed reported to be nearly 40 miles per hour, Huskisson died later the same day.



To give a History of Railway Signalling some sort of context, it is useful to start with a summary of the history of ‘the railway’ itself.



One can well imagine Stephenson’s feelings as Huskisson stumbled into the Rocket’s path, but consideration of the reasons why he was unable to stop in time brings us back to the theme of Signalling and its development.



The railway, by which we mean vehicles with flanged metal wheels running on a guideway of metal rails, has been in existence for less than 250 years. It has proved to be the most efficient form of land transport, in the sense of being able to move heavy loads at high speeds over long distances, yet devised. It is, however, the qualities that give the railway its efficiency and the ability to move heavy loads along a lowfriction bearing surface that create the need for the system of signalling and control that we will look at in this paper. For the moment, consider your own experiences as a car driver, and think about the ability to stop quickly from various speeds – we shall return to this theme later on.



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4 The Beginnings of Signalling Those of us used to driving cars are familiar with the concept of ‘stopping distance’. To stop a car travelling at speed requires a distance proportional to that speed. The Highway Code tells us that to stop from 30 mph, even with the high level of friction available between rubber tyres and a dry, well-maintained road surface, will require 23 metres or 75 feet, and under the same conditions from 60 mph, not twice but over three times as far, 73 metres or 240 feet. But for a train rolling on steel wheels along a guideway of steel rails, levels of friction, and hence adhesion, are much reduced. In the case of a modern passenger train such as the diesel-powered ‘Inter-City 125’, the distance required to stop from its maximum speed of 200 km/h (125 mph) is nearly one and a quarter miles, even with superior brakes. This is not an unreasonable comparison; back at the dawn of the railway age, the problem uppermost in the minds of engineers and operators was how to keep them going rather than how to get them to stop safely. The rudimentary braking technology available at that time would not stop a train travelling at 50 mph on the level in much less than three-quarters of a mile. So, with trains hauled by steam locomotives that could reach speeds of 50 mph or more, you could not rely on a driver who saw an obstruction ahead being able to brake sufficiently hard to avoid colliding with it. Neither could he steer out of the way, so there arose the need for new disciplines that would ensure a safe separation of moving trains by means of signals to drivers from the lineside.



in a section, out of sight between two policemen, a member of the train crew (usually the guard) had to run back along the line as far as possible to show a hand signal when the next train approached. Given the poor efficiency of train brakes in those early days, this would have required a run of at least half a mile, or more if time allowed. In the absence of physical safety devices, signalling at the dawn of the modern railway age depended on a detailed code of rules, procedures and instructions that the railway’s servants were expected to follow with military discipline. Where mechanical failures led to accidents this was often due as much to lack of experience of where the system might fail as to the failure itself. Incidentally, when a modern train driver doesn’t know a signalman’s name, he will often address him as ‘Bobby’, a reminder of his railway policeman ancestry.



5 Fixed Signals Although Time Interval working remained in widespread use up until the 1860s, fixed lineside signals began to appear as an alternative to the policemen’s hand or flag signals in the late 1830s. At first these simply mimicked hand signals on a larger scale, with arrangements of moveable flags or discs and coloured lights being mounted on tall posts and operated by a policeman, but had the advantage of being visible at greater distances. Signals were displayed in accordance with the convention that Red indicated ‘Stop’, Green ‘Caution’ and White ‘Clear’.



Before proceeding, it is worth remembering that at this time none of the facilities regarded today as essential to safe operation existed: x



no telegraphs, telephones, or other form of instant communication; x no lineside signals; x no brakes at all on the majority of vehicles; x no centralised control of points; x no whistles on locomotives until 1833. The first signalling systems were therefore entirely humanbased, the line being divided into sections of approximately two miles with hand signals being given to train drivers by Railway Policemen stationed at the beginning of each section. A policeman would indicate a clear way ahead by standing facing an oncoming train with his arm outstretched. After a train passed him and entered the section he would assume a ‘stand at ease’ position. He would continue to signal an obstruction, if another train approached his position, until a time interval (typically 7 – 8 minutes) had elapsed, after which he could permit a following train to proceed, but under caution. In this way train separation was maintained, and to allow policemen to impose consistent time intervals, the railway company would issue them with sand glasses or ‘egg boilers’. The Time Interval system of signalling did have one insurmountable drawback. If a train broke down and stopped



Figure 1: Great Western Railway ‘Disc and Crossbar’ signal



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Adoption of a white light for ‘clear’ seems odd to us nowadays, but in the early to mid-19th century, before the widespread use of gas (and later electricity) to light houses, roads and public spaces, the countryside at night was profoundly dark, and there was little chance of confusion between signals and external lights. What also appears as odd to later generations is the accepted practice of a signal conveying ‘Clear’ or ‘Proceed’ simply by the absence of a Danger indication. Red flags or discs would be turned edge-on to allow a train to proceed, and in the most famous example, a ball signal was displayed at the approach to Reading Station on the Great Western Railway and described in that railway’s Regulations thus: ‘A Signal Ball will be seen at the entrance to Reading Station when the Line is right for the Train to go in. If the Ball is not visible the Train must not pass it’. It was not until the late 1870s that a serious accident called this arrangement into question and the practice was changed. In 1841 Charles Hutton Gregory designed a Semaphore signal to be used on the London & Croydon Railway, and the result was the first example of what we would now recognise as a ‘railway signal’. Although the signal was fixed in position alongside the track, it still needed a man there to operate it. In 1843, Gregory built a contraption of levers and stirrups, by which a number of signals and points could be operated by one man from a central location, together with a very basic form of ‘interlocking’ to prevent a signalman from operating points or signals in a way that could lead to a derailment or a collision. This was however extremely crude, and didn’t provide what we would now understand as true interlocking whereby one lever movement must be completed to allow another to be moved, a development that would not appear until the 1860s.



6 The Coming of the Telegraph Despite the advances in lineside signal design, the method of keeping following trains apart by time interval working continued. What was needed was a simple and reliable form of communication between the policeman at one end of a section and his colleague at the other that would allow trains to be operated according to a system of ‘space interval’ working rather than the fragile protection offered by the policeman’s sand-glass. The device that would provide this communication and start the long and intricate story of electrical railway safety devices was the Cooke & Wheatstone electric telegraph, first demonstrated in 1837. Early telegraph instruments used a pointer or ‘needle’ that could be moved to the left or right to allow messages to be sent by spelling out words letter-by-letter using a telegraphic code (of which the American Morse Code was only one of many). In the railway application this allowed a policeman to report a train entering the section to his colleague down the line, who could in turn could report back when it left the section. If the train didn’t arrive, or arrived incomplete, and no report was received, any following train would be stopped and detained.



Figure 2: Block Telegraph instrument In this way, a system of signalling in which the whole of a train entering a ‘block section’ must be positively observed to have left it before another train can be admitted was a practical possibility. This system came to be called ‘Absolute Block’ and began, slowly, to be adopted by the more responsible railway companies. For example, by 1852, the forward-thinking Great Western Railway had installed lineside wires on all its main routes for the electric telegraph. The photograph shows a typical Block Instrument that evolved out of the experiments and problems with the original telegraph instruments. It is capable of showing three indications – ‘Line Blocked’ (the normal condition of the section), ‘Line Clear’ and ‘Train On Line’, and in conjunction with a single stroke bell for exchanging coded messages, provides the basis for the Absolute Block system that eventually controlled train movements throughout the British railway network. A useful spin-off of the spread of railway telegraphs across Britain was the introduction of ‘Standard’ or ‘Railway’ time (the concept of Greenwich Mean Time wasn’t introduced until 1880). At a time when ‘Bristol’ time was some 15 minutes later than ‘London’ time, this was in itself a minor social revolution.



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7 A Digression - Railway Braking systems Although strictly outside the scope of a study of signalling, mention must be made of railway brakes, without which a train cannot be controlled and any signalling system is of little or no use. Early train brakes were primitive in the extreme; a mechanical brake being provided on the locomotive or its tender, and a similar arrangement on a brake van at the rear of the train. Because there were no brakes at all on the wagons or passenger coaches in between, stopping and starting a train required a fine degree of co-ordination between driver and guard (the driver would use the locomotive whistle to convey his instructions) to synchronise the braking being applied and avoid the train being squeezed, or even worse, stretched, and couplings broken. Throughout most of the mid-Victorian era from 1840 to 1890, railway engineers sought to devise means of providing ‘continuous brakes’ which would act on all vehicles throughout a train. Most of these were unsuccessful, some spectacularly so, but in the absence of legislation, the railway companies kept experimenting with systems using rods, chains, hydraulic, steam and air pressure, and vacuum. It took a truly horrific accident to force the Government to make continuous brakes, acting on every vehicle and automatically applied in the event of vehicles becoming inadvertently detached from a train, a legal requirement.



8 A Word about Accidents At the beginning of the 21st century we are accustomed to the concept of ‘engineering for safety’, where design and implementation of complex systems such as aircraft or industrial plants whose failure can have serious – or, in the case of nuclear facilities, unimaginable – consequences are subjected to rigorous processes of review and analysis throughout their lifecycles to identify, record, and control all possible hazards. Development, adoption and use of these processes has been very largely dependent on experience and understanding of systems and their behaviour. In the middle years of the 19th century, however, with railway engineering and safety disciplines still in their infancy, there was little or no such experience on which to draw; the evolution of safety was slow and mostly reactive, a major accident frequently acting as the incentive to improve equipment, rules or practices. Legal regulation of the early railways was surprisingly limited, the best description of the Government’s philosophy being ‘supervision without interference’. An Act of Parliament passed in 1840 allowed the Board of Trade (the Government’s economic advisory committee) to appoint Railway Inspecting Officers. These were serving officers recruited from the Army’s Corps of Royal Engineers with powers to inspect and report on new railways and approve their opening for public use, and to investigate the causes of railway accidents.



Unfortunately, it was very seldom the case that innovation in the field of railway signalling was followed by a headlong rush by railway companies to implement the new technology. Many of the devices and systems that we now think of as providing undeniable safety benefits were available for many years before companies would agree to install them, either because of the costs involved, or often because they had been developed by and used on ‘another Company’s railway’. For example, slow take-up of the telegraph block system was in no small way due to the stubbornness and, one might be forgiven for saying, arrogance, of railway company directors, an attitude clearly demonstrated by the Company Secretary of the London, Brighton & South Coast Railway in a muchquoted reply to the Board of Trade regarding the Inspecting Officer’s report into a serious accident in Clayton Tunnel in 1861: “My Board feel bound to state frankly that they have not seen reason to alter the views which they have so long entertained on this subject, and they still fear that the telegraphic system of working recommended by the Board of Trade will, by transferring much responsibility from the engine drivers augment rather than diminish the risk of accidents”. Note those words - ‘Recommended by the Board of Trade’ – it was to be nearly 30 years before a particularly catastrophic accident forced the Government to give legal powers to the Board of Trade to not just recommend, but demand, the adoption of basic safety systems on passenger railways. In the meantime, Inspecting Officers continued to investigate every accident, recommending in one report after another adoption of the three basic safeguards of railway safety, namely interlocking of signals and points, Absolute Block working and continuous automatic braking systems on passenger trains, frequently shortened to the memorably monosyllabic ‘Lock, Block and Brake’. The history of railway signalling in the Victorian era is thus linked closely with that of accidents. For further insights readers are encouraged to obtain and read the original and arguably the best study of British railway accidents, ‘Red For Danger’ by L. T. C. Rolt, first published in 1955 and reprinted and updated a number of times since then.



9 The Lighter Side - Other Safety Devices Reading contemporary newspapers from the Victorian era, one can feel a sense of déjà vu reading journalists’ and correspondents’ criticism and condemnation of the railway companies for their lack of humanity in the treatment of staff (24 hour shifts were not uncommon) and apparent pursuit of profit at the expense of safety. One of the most caustic critics of the railway industry was the magazine Punch, which first appeared in 1841 and relentlessly pursued and lampooned the railways well into the 20th century.



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To an extent that seems extraordinary to us today, endless curious suggestions were sent to newspapers, and even to the railway companies themselves, including a demand that all passengers should be issued with inflatable suits to protect them in the event of a collision. One of the most imaginative and at the same time least practical was the suggestion made in a letter to the Chairman of the London & South Western Railway, also in 1841. This required sacks of wool to be suspended at the front and rear of the train and in between the coaches so that in the event of a collision, the energy would be absorbed by the woolsacks and the passengers would thus come to no harm.



10 The late Victorian era Returning to the timeline of signalling development, Britain’s railways had by the 1870s voluntarily adopted some if not all of the triple safeguards of Lock, Block and Brake. Once the issues of communication along the railway to allow Absolute Block operation, and of giving consistent signal indications to drivers had been sorted out, there remained the important consideration of how to apply signalling safely to the ever more complex station and junction layouts that were developing. Semaphore signals were by this time in widespread use to control train movements, being operated mechanically from interlocked lever frames in signal boxes. The development of mechanical interlocking provides a good example of the flood of railway engineering innovations appearing in the later years of the Victorian era. From the 1860s, the complexity of stations and junctions had provided the incentive for development of more reliable and positive methods of interlocking. A host of inventions appeared, with a number of different companies seeking to patent their particular method of interlocking and then convince the railway companies of its virtues. By the 1890s, some 40 different methods of interlocking – all achieving the same end - had been designed, built and patented. There were lever frames using tappets, grids, rockers, tumblers, cams and studs. There were frames with locking actuated by rocking shafts, hook racks, soldiers and twist bars, and interlocking composed of dogs, darts, half locks, swingers and diamonds. Mechanically interlocked lever frames reached a peak of complexity and size in the closing years of the 19th century, the record being set by a frame containing a single continuous row of 295 levers in a signal box at York. Some of the interlocking mechanisms were of quite astonishing ingenuity, but were at the same time extremely difficult to maintain - the designs which survived the longest therefore tended to be the simplest and most robust. Even today, over a dozen different designs are still in use in Network Rail’s several hundred mechanical signal boxes.



The one area where the march of safety had been slow or stationary was the adoption of continuous brakes. Mention has already been made of the proliferation of braking systems, with advantages being claimed for each by their supporters. In 1875 a trial of 11 different braking systems had taken place at Newark, which eventually demonstrated clear superiority of the automatic vacuum brake. It was not until 1889 that the issue would finally be decided in a shockingly dramatic and tragic way.



11 Armagh 1889 – an ‘Event Catalyst’ On 12 June 1889, an excursion train of the Great Northern Railway of Ireland left Armagh for the seaside town of Warrenpoint, on the shore of Carlingford Lough. Nearly a thousand passengers, over half of them Sunday-school children out on a treat, were packed into 15 coaches, and as was the usual practice with such excursions, the coach doors were locked. It had been expected that the train would be made up of only 13 coaches, that the locomotive to be provided would be adequate to the task of taking the train over the steeply-graded line, and that an experienced driver would be available. All of these expectations proved to be wrong. Two extra coaches were added shortly before departure, the locomotive was thus inadequate to its task, and the only driver available had never driven a train over the line before. Barely two miles from Armagh, the locomotive stalled on a 1 in 75 gradient through lack of steam. After some discussion between the train crew, the decision was taken to divide the train to allow the loco to reach the summit with the first five of the 15 coaches. What made an already bad situation worse was that the train was fitted with an early, non-automatic system of continuous braking called the ‘Simple Vacuum’, a pernicious and potentially lethal system in which vacuum created by the locomotive was piped through the train and used to apply the brakes. By contrast, in the automatic vacuum brake, which was by then already used by a number of British railways, and remained in use until the late 20th century, the vacuum holds the brakes off. Atmospheric pressure is used to apply the brakes when air is admitted to the brake pipe through the driver’s brake valve, or through any opening in the pipe, as when a vehicle becomes detached. It was equally unfortunate that the line was still being worked under the time interval system, and that the train crew, occupied with dividing the train, had neglected to take any steps to protect it. Although they must have realised the potential danger of their course of action, the train was divided between the fifth and sixth coaches, the Simple Vacuum brake thereby becoming totally ineffective with the only brake remaining to hold the train on the gradient being in the van at the rear. And, inevitably, when the locomotive tried to restart on the gradient, it set back slightly and bumped the detached



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coaches, pushing them over the stones which the crew had placed under the wheels in a futile attempt to hold them on the gradient. The coaches then ran away down the 1 in 75 gradient gathering speed, and collided with the following train (which had been authorised to leave Armagh under the time interval rules) at over 40 mph, completely destroying the last three vehicles, killing 78 passengers (a third of them children) and injuring a further 260. This disaster, which eclipsed all previous British railway accidents in its scale and casualties (including the collapse of the Tay Bridge in 1879), proved to be a defining moment in British railway and signalling history. Public opinion was so outraged that the British Government was compelled to pass – less than three months later - the Regulation of Railways Act 1889 which finally gave the Board of Trade’s Railway Inspectorate legal powers to compel railway companies to provide the following safeguards:



The other signalling technology development of major importance during the 1890s was the widespread introduction of the electric token system of single-line working invented in the 1870s by Edward Tyer. Now, instead of the old - and ultimately fallible – human methods using telegraphic orders or staffs and tickets, the issuing of a single line token – the visible authority for a driver to enter a single-line section could be electrically controlled so that one could be issued at either end of a section, wherever it was needed. With this method, the need for hand-written tickets or orders, and the hazardous work-arounds that had been required when, for example, an operating problem left a train at one end of the section and the token at the other, became things of the past.



x



to install interlocking between points and signals; x to adopt the Absolute Block system to control trains (rather than the time interval method); x to fit continuous, and automatic, brakes to all passenger trains. Thus did ‘Lock, Block and Brake’, the basic pillars of present-day railway safety, at last become law. Subsequent technical development, as we shall see, tended more towards increasing efficiency and eliminating human error, although for many years this would be far more successful in protecting signalmen, rather than drivers, from the consequences of their mistakes. We can therefore consider the modern signalling era as starting from this point.



12 Signalling and Operation - developments after 1890 Following the 1899 Regulation of Railways Act, British railway signalling entered a period of renewed development, invention and innovation. Now that the foundations of modern signalling practice had not only been laid but firmly cemented in place by statute, the way was opened for further improvements, both technical and procedural. As adoption of Absolute Block working was now no longer a matter of choice, there was a proliferation of styles and types of instruments, and methods of operation, as we have already seen with lever frames and interlocking. Two-position and three-position block, one-wire and three-wire instruments, rotary and sequential block - all had their adherents. One of the most successful and widely-used of the ‘enhanced’ block systems was Sykes Lock & Block. This not only integrated the exchanging of messages between signalmen at the ends of a block section into the operation of the block instruments but also mechanically interlocked the signals with the block working and the block working with the passage of the trains through the section. This made operation by manual block methods as near foolproof as it could be.



Figure 3: Tyer’s Single Line Key Token Instrument As with other signalling developments, a basic idea would often be developed in various ways by different railway companies or manufacturers. Single line instruments took many forms, and the ‘tokens’ came in all shapes and sizes including tablets, staffs and keys. The photograph shows a Tyer’s Key Token instrument, many of which are still in use on Network Rail and British heritage railways.



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13 The First Power Signalling Systems By the end of the 19th century, the use of electricity in the service of railways already had a firm foundation – Volk’s Electric Railway in Brighton, the first electric line in Britain, opened in 1883, and the first of the deep-level London ‘tube’ railways, the City & South London, carried its first passengers in 1890. As far as signalling was concerned, the application of electricity had been limited to the telegraphs, early telephones, and some simple train detection devices.



impressed with the ‘Low Pressure Pneumatic’ system, and on his return ordered a trial installation to be undertaken at Grateley, between Andover and Salisbury, using air compressed to only 15 pounds per square inch to operate points and semaphore signals. In this case the ‘levers’ were in the form of pull-out slides, with mechanical interlocking between them, operating valves to control the compressed air.



Over the next few years, however, this was to change with the coming of power signalling systems. These would take the brute force out of signalling and change the focus of the signalman’s job to being a regulator of traffic rather than a manipulator of machinery. A number of different power signalling systems emerged at this time, each with its own disciples and claimed advantages. The first to appear, in the closing months of the century (January 1899) was the electro-pneumatic installation (compressed air controlled by electrically-operated valves) at Granary Junction, Bishopsgate (just outside Liverpool Street).



Figure 5: Low-Pressure Pneumatic frame at Grateley - 1901 It is interesting to note that Jacomb-Hood’s rationale for adoption of the Low Pressure Pneumatic system was that, as it involved no electrical devices, its installation, maintenance and care could be carried out by skilled mechanical fitters with no electrical knowledge, a good example of selection of technology being made on the basis not only of suitability to the application but also to the operational environment.



Figure 4: Interlocking Machine at Granary Junction - 1899 The interlocking ‘machine’, with its rotary handles in place of levers, and parallel shafts reminiscent of a table football game, was an American import and, as such, was viewed with considerable suspicion by the conservative railway establishment. It had none of the features that would come to be associated with later power signalling installations such as an illuminated track diagram, and even the mechanical ‘fouling bars’ that had long been fitted on the track to prevent points being moved under a train were retained. But it showed what could be done to take the hard manual labour out of controlling a busy layout, and was followed immediately by other, different, systems. In 1900, the signal engineer of the London & South Western Railway, J W Jacomb-Hood, visited America to inspect a number of signalling installations. He was particularly



Yet another type of power signalling being introduced at this time was the ‘All-Electric’ system, first brought into use at Crewe, also in 1899. The system was designed and manufactured by the London & North Western Railway at their Crewe works, as had all their mechanical and electrical signalling apparatus for over twenty years (the L&NWR had, it seems, a deep and abiding distrust of contractors), and used a miniature lever frame with two rows of levers spaced 4 - 4½ inches apart so as to allow the use of existing interlocking components from full-sized frames. These systems offered significant advantages in extending the length of the signalman’s reach as operation of mechanical points was limited by Board of Trade regulations to 200 yards from a signal box (this was extended to 350 yards in 1925, where it has remained ever since). Power operation, whether electro-pneumatic, ‘low-pressure pneumatic’ or ‘all-electric’, opened the way to a major extension of signal box control areas, which the development of other devices would push even further, and the early years of the 20th century saw some extremely complex signalling installations brought into use. The largest of these, commissioned at Glasgow Central in 1908, was controlled from a single frame of 374 miniature levers, all mechanically interlocked.



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14 Emergence of Familiar Concepts



15 Train Detection



The early years of the 20th century were characterised by the development, all over Britain, of what we would now call ‘urban transit systems’. First to come had been the underground railways in London, followed by the deep-level Tubes. Next on the scene were the new electric tramways, providing fast (and clean) door-to-door transport at frequent intervals. When in the early 1900s, the tramways started pushing out into the suburbs, particularly in South London, the railway companies were very concerned that tramways were trespassing on their turf and started on a programme of electrifying their suburban railway networks so that they could compete with the tramways in an attempt to win back their lost passengers.



Irrespective of how the points were moved (electric motors or compressed air), or the signals shown to the drivers (arms or lights), extension of a signalman’s area of control created one particular and vital requirement: that of positively detecting the presence of a train at a particular location and using the information to protect it against other trains moving towards it, or points moving underneath it.



In the beginning, the electrified services were operated using traditional mechanical signalling methods of the type we have already seen. However, as the electrified networks spread and levels of train service increased, it became obvious that the ability to operate a suburban network with frequent and fast electric trains, together with longer-distance steam-hauled services required some radical improvements in the signalling arrangements. Not only was it necessary to increase line capacity, but the ability to keep trains moving under all weather conditions, particularly the dense fogs which London and the other cities suffered, demanded an improved signal. In November 1921 A E Tattersall read a paper to the Institution of Railway Signal Engineers on ‘Three-Position Signalling’, which turned out to be another defining moment in the history of signalling. This paper examined the future direction of signalling, what signals should be presented to drivers, how these should be given, and how the system should be controlled. As a result, the Institution set up the ‘Three Position Signal Committee’, which reported in December 1924 that future signalling developments should adopt three-aspect colour-light signals as their basis, including the long-argued use of Yellow as the colour for Caution signals. With this agreed, the way forward was finally clear for signalling using the aspects we know today. A further outcome of the IRSE’s Committee (now the ‘ThreeAspect Signal Committee’), in addition to the preference for colour light rather than semaphore signals, had been the recommendation that a fourth aspect be provided to allow differentiation on lines carrying mixed traffic. In 1925, the resignalling of London’s Blackfriars and Holborn Viaduct stations (now part of the Thameslink route) introduced the first four-aspect signal. Introduction of the Double Yellow, or ‘preliminary caution’ aspect, allowed not only more trains to be accommodated on a given section of line, but for them to run closer together. High-performance electric trains, stopping frequently and rarely reaching more than 50 mph, could drive confidently at this speed and not brake until sighting the single yellow aspect, whilst heavier, faster and less well-braked steam trains would start to brake on sighting the double yellow aspect, giving them double the braking distance.



The earliest practical means of achieving this, the Track Circuit, had long since come of age, the original patent for using an electric current flowing in the rails to detect the presence of a train had been filed in the USA 50 years earlier, in 1875. But its use had so far been limited to isolated sections within manually signalled areas to remind the signalman of a train waiting out of sight of the signal box; the early power signalling installations such as Grateley and Granary Junction had managed without them. However, from the 1920s, the track circuit rapidly gained ground as the essential safety feature of a signalling system, and as schemes grew in size and complexity, track circuiting was always there. One of the track circuit’s principal benefits was its ability to control signals (either power-worked semaphores or colourlights) without human intervention over long stretches of line. Previously, with Absolute Block working, many hundreds of small intermediate or ‘break-section’ signal boxes had been provided to divide up stretches of line between stations and so increase line capacity, allowing trains to run at more frequent intervals, each of these having to be manned for two, or sometimes three, shifts every day. Now, these remote and often inaccessible boxes could be replaced with one or more sections of ‘automatic signals’ so that trains could safely follow one another at closer intervals, each train protecting itself by replacing the automatic signals to Danger as they passed, and allowing them to show ‘Proceed’ again when they had passed beyond the next signal ahead. This method of operation, where signals are controlled at and between signal boxes by track circuits rather than signalmen communicating with block telegraph instruments, is used up to the present time on all main lines and many secondary lines in Britain, where it is known as ‘Track Circuit Block’. Where sections of automatic signals were provided so that signal box control areas extended over several miles, there was a need for the signalman to know what was going on beyond his field of vision. The spread of power signalling installations with continuous track circuiting was accompanied by the appearance of the now familiar illuminated track diagram. The first was installed in 1905 at the station now called Acton Town as part of an electropneumatic signalling installation on the newly-electrified District Railway, and their use eventually became universal.



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From 1930 onwards, therefore, developments turned towards signalling systems that could be controlled and interlocked by entirely electrical means. The mechanical interlocking of the miniature lever frames, and the watchmaker’s precision required to install and set them up, would be progressively replaced by electrical circuits, control panels, switches and push-buttons.



Figure 6: Illuminated Diagram at Acton Town, District Railway Even away from the major station and junction areas, where power signalling had not yet taken over from Absolute Block, track circuits started to appear as aids to the signalman, for example to prevent a lever being worked to move points under a train, or to remind him of a train standing at a signal. Track circuits could also be used to provide controls on block instruments which, together with electrical proving of the position of the signals, would impose the same discipline of sequential block and signal operation on the signalman as Sykes Lock & Block did mechanically.



16 The 1920s Development of power signalling reached a peak in the 1920s with the coming together of track circuits, colour-light signals, power-operated points and miniature lever frames in some of the most complex signalling schemes yet undertaken. When the lines through London Bridge to Cannon Street and Charing Cross were electrified this included total rebuilding of the layout at Cannon Street and new signal boxes with mechanically-interlocked miniature lever frames at Charing Cross, Cannon Street, Borough Market Junction and London Bridge. With a similar scheme in progress at the same time in Manchester, this period marked the zenith of miniature lever frame technology but also the beginning of the end of the era of mechanical interlocking. Operation and regulation of train services from the new centralised power signal boxes at London Bridge and Manchester Victoria was undoubtedly far more efficient than it had been at the time when control of the layout was dispersed between two, three or more signal boxes. However, a down-side of the intricacy and compactness of the interlocking mechanisms was that modifications (such as when train lengths increased and there was a need to move signals) were very complicated, difficult, time-consuming and hence costly.



An interesting and very successful development at this time was the electrically-interlocked miniature lever frame, designed by the Westinghouse Brake and Saxby Signal Company (now Invensys Rail), which followed the traditional British practice of providing a lever for each signal and individual set of points, but with the interlocking between the levers achieved by means of contacts and electromagnetic locks on the levers. To a signalman, it looked, felt, and operated like any other lever frame, but the flexibility provided by the electrical interconnections made this one of the most popular methods of signalling control ever devised and machines totalling nearly 10,000 levers, were built by Westinghouse and exported all over the world. Although the last new frame of this type was built in 1961, the ability to rewire, reconfigure and recycle them meant that second-hand frames of this type were still being installed up until the 1980s.



17 The Emergence of Route Setting Mention of the ‘traditional British practice of providing a lever for each signal and set of points’ is an appropriate way of introducing the concept of Route Setting, which emerged in Britain in the 1930s and has become the principle of operation of all signalling systems developed since then, including recent innovations such as computer-based interlocking (CBI) and radio-based cab signalling. Practice in Continental Europe, particularly in France, had since the turn of the 20th century been to allow a signalman to operate a single control device or ‘levier trajecteur’ to set up a complete route through an interlocking area from the signal that would authorise the train’s movement to its point of destination ahead. In 1922 the Great Western Railway (GWR) installed a trial ‘route setting’ signalling system at Winchester (Chesil) station, on the now long-abandoned cross-country route from Didcot to Newbury, Eastleigh and Southampton. The control machine was a miniature frame, with 16 levers, and movement of one lever through a number of intermediate checking positions would move all the necessary points (if they were free of interlocking or track circuit locking), prove track circuits in the route Clear, and finally lower the signal, an electrically-operated semaphore, for the train to proceed. After four years of operation the GWR was sufficiently impressed with this trial to go ahead with a major resignalling scheme using route-setting lever frames at Newport East (1927) and Newport West (1928). Although these installations were revolutionary in themselves, the GWR did not go so far as to abandon Absolute Block working between



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the boxes. Nor did they pursue the route setting idea any further, reverting to conventional miniature lever frames for later major power signalling installations at London Paddington, Bristol and Cardiff. Even the trial installation at Winchester lasted only until 1933, when it was replaced by a conventional (full-sized) mechanical lever frame.



Once embarked on this course, the L&NER vigorously pursued the concept of the ‘relay interlocking’. Widening of the East Coast Main Line north of York was going ahead, funded by the Government as part of the scheme to relieve the unemployment of the early 1930s, and as part of this work, a new signal box was commissioned at Thirsk in 1935, incorporating the first route setting panel on a British railway. The method of route-setting used at Thirsk, and at many major interlockings for the next thirty years, was that known as ‘single control switch’, where operation of a single thumbswitch (or in some interlockings, a push-button) would set up a complete route, providing the interlocking and controls would allow it. In later years Westinghouse trademarked this as the ‘One Control Switch’ or ‘OCS’ system, which reached its peak of achievement with the massive installation commissioned at York in 1951, controlling over 800 individual signalled routes and for some years the biggest relay interlocking in the world. A minor but nonetheless significant event that took place in 1938 should be mentioned at this point, for in that year a small control panel and relay interlocking were commissioned at Brunswick goods station in the Liverpool Docks. This used an American technique of route setting, requiring the signalman to operate first a rotary switch and then a pushbutton to define respectively the start point and the destination of a signalled route. Its manufacturers, the General Railway Signal Co of Rochester, New York, had coined the name brand name ‘NX’ to describe this system - the ‘Entrance-Exit’ panel had arrived.



19 ‘Automatic Train Control’ Figure 7: ‘Route-Setting’ lever frame at Winchester - 1922 As a footnote to this part of the history of railway signalling, the then new Ministry of Transport set up, in 1925, Britain’s first electric road traffic signals at the junction of St James’s Street and Piccadilly. Not only did this use three-aspect colour-light railway signals, but they were controlled by a police constable from a miniature lever frame, thereby demonstrating the principle that technological advances are best made by taking cautious steps forward and using hardware that someone else has already developed.



18 ‘Levers versus Panels’ In the early 1930s, divisions were appearing between British signal engineers as to how interlocking technology should develop. On the one hand, the Southern Railway, with its intensive suburban electric services, continued to install fouraspect colour-light signals worked from miniature, (but by now, electrically-interlocked) lever frames. Elsewhere, the London & North Eastern Railway (L&NER) was developing the concept of a completely electrical system with no levers at all and interlocking carried out in the control circuits by relays, operated by switches on a control panel.



I mentioned earlier that for many years railway signalling development tended to focus on protecting signalmen, rather than drivers, from the consequences of their errors. From the earliest days of railways and signalling, the fatal flaw in any system using visual signals has been the possibility of the driver overlooking, misreading or just ignoring the signal giving him authority to proceed. Accidents without number have occurred through drivers failing to see, or failing to obey, signals at Danger, the situation that we nowadays call a Signal Passed At Danger, or SPAD. Attempts to solve the problem are almost as old as the railways themselves. In 1840 the London & Birmingham Railway experimented with a means of giving audible and visual signals to a driver on a locomotive if he passed a signal at Danger by means of a lever on the track which engaged a lever below the locomotive to sound a whistle and turn a red lamp in the driver’s face. Adoption of such a device, however, at a time when railway companies were arguing against even the use of block telegraphs and other aids to safety on the basis that they would make signalmen and drivers careless, would not happen for many years. In 1900 the GWR, prompted by a fatal SPAD accident at Slough, started experiments with an electro-mechanical system of ‘Automatic Train Control’ (ATC) which sounded a



15



horn in the locomotive cab to warn the driver on the approach to a signal showing Caution, or a bell to confirm that it was at Clear. If the driver did not acknowledge the horn signal within 2 – 3 seconds, the train’s brakes (continuous vacuum brakes on the GWR) would be applied automatically and bring the train to a stop. The system, which was activated by contact between a ramp mounted on the track and a ‘shoe’ on the locomotive, was subsequently installed on the GWR’s main line from Paddington to Reading, and eventually (by the early 1930s) all over the GWR network, from which it finally disappeared only in the 1970s, well into the British Railways (BR) era. Until nationalisation in 1948, railways in Britain had been private, commercially-driven bodies, each with its own operational and engineering practices, preferences and prejudices, as illustrated by the proliferation of designs for lever frames, signals, and block telegraphs discussed earlier. Even when 120-plus railway undertakings were combined into the ‘Big Four’ companies (Great Western, London Midland & Scottish, London & North Eastern and Southern) in 1923, many of the old ways remained. For a railway to adopt a system developed by another company was unthinkable and away from the GWR, widespread adoption of ATC or any other protection or warning system did not occur until well after nationalisation. During the intervening years, accidents caused by drivers ignoring or misreading signals consequently continued to occur, and the Railway Inspectorate continued to argue in vain for adoption of ATC. After the formation of BR in 1948, one of the first actions of the new British Transport Commission was to undertake the installation of ATC throughout the principal rail routes of its network. Trials were started, using a system of track-mounted magnets to operate a horn or a bell in the driver’s cab, similar to the GWR ATC, but with the addition of a visual indicator to remind the driver that he had received a warning, and that it had been acknowledged. Soon after the new system went on trial on the East Coast Main Line in 1952, a catastrophic double collision occurred at Harrow in which 112 passengers and train crew were killed, and the Inspecting Officer had no hesitation in stating once again that ATC would have, without a doubt, prevented this accident.



Figure 8: Track-mounted magnets of BR-AWS system



By the time trials of the new system had been completed, reports prepared and approval given, work had only just started before another horrific rear-end collision following a SPAD, in fog, at St Johns in south-east London. Installation of the Automatic Warning System or ‘AWS’ as it came to be called, went ahead steadily and gradually extended to all BR’s main lines and most of the secondary lines, where it remains in use. As an interesting contrast to the timescales for development of ATC in Britain, railways in France were being equipped with a warning system similar to the GWR ramp as early as 1875. Called the ‘Crocodile’, it acted in a similar way to ATC on the approach to a signal (that is, as a vigilance device), and required the driver to acknowledge a warning within 4 – 5 seconds, or the brakes would be applied. It has been suggested that GWR’s ATC was based on the Crocodile concept but, whereas ATC has now passed into history, the wavy ramp of the Crocodile remains a familiar feature on main lines throughout France, Belgium and Luxembourg, over 130 years since its introduction.



20 Automatic Train Protection AWS is a ‘warning system’, and is required to work with trains of widely differing weights, speeds and performance characteristics. For this reason it does not have the ability to give the unequivocal Stop command of the ‘trainstop’ devices used on London’s Underground and other metro systems. Also, because of the driver’s ability to acknowledge a warning and prevent the brake application, it will not provide protection in cases where signals are deliberately ignored or misunderstood. The only system that can provide this level of protection, as well as constant supervision of speed, is Automatic Train Protection or ATP. Following several serious SPAD accidents in the late 1980s the Government made an undertaking that BR would fit ATP throughout its network within five years (this somewhat rash promise was later modified to ten years). Because no British signalling manufacturer could at that time deliver an off-theshelf technical solution, BR initiated two trial ATP installations. The two main routes between Paddington and Bristol were equipped with a system called ‘TBL’ from Alstom in Belgium, and the German ‘Selcab’ supplied by Alcatel (now Thales) was installed on the Chiltern Line routes between Marylebone and Banbury. Both systems used a system of track mounted loops and transponders to relay information from the trackside to the train regarding the state of the signals and the permitted speed on the line ahead so that the driver could control the train within an envelope of protection, under the supervision of the ATP. Implementation of both trial systems was well under way by 1994, when the newly-formed Railtrack announced that a financial case for system-wide installation of ATP could not be made and so would not proceed further. The trial installations were nevertheless completed, and will continue in service until full transmission-based signalling designed to European interoperability standards is installed in the future.



16



When BR initiated its ATP trial projects in 1991 the Channel Tunnel was still under construction, and realisation of the ‘European Rail Traffic Management System’ concept (ERTMS) to allow operation of trains with a common signalling system throughout the member states of the European Union was some years away. Having already recognised that it would be many years before ERTMS would be implemented throughout the British railway network, Railtrack had started investigating an interim train protection solution. The Train Protection & Warning System (so called because its trainborne equipment combines the function of a trainstop with that of the existing AWS) was based on available technology and effectively offered a ‘low-tech’ solution to mitigate the consequences of SPADs. Trials of the equipment were put in hand in 1996 on the Thameslink network, and the Thameslink (now First Capital Connect) electric multiple unit (EMU) trains were fitted with the train-carried equipment. During the time that this work was going on, two major SPAD accidents occurred, firstly at Southall in September 1997, and then at Ladbroke Grove in October 1999. The latter accident occurred less than two months after Parliament had enacted the Railway Safety Regulations 1999 in which the provision of a system of train protection on all trains, and at ‘selected signals’ (those protecting junctions and points of conflict) was mandated by law, to be completed by the end of 2003. At the time of writing (2010) TPWS is installed at 12,000 ‘selected signals’ throughout the British main line network and on all trains, where it will remain in use, together with AWS, for the foreseeable future.



21 Towards the Present Day We left the railway signalling scene at the outbreak of war in 1939. For obvious reasons, any advances in signal engineering were effectively stopped for the duration of the war, the railways’ first priority being to just keep going. Major schemes such as the resignalling of York and electrification from Liverpool Street to Shenfield were put on hold, and others were abandoned, never to be resurrected. Meanwhile, the railway system struggled on in the face of shortages of material, depletion of its manpower, and enemy attack.



way forward (except on the Southern Region, successors to the Southern Railway, who were still busily installing miniature lever frames in the South London suburban area), and implementation of AWS got under way, as we have seen, although funds for new major schemes were limited until the BTC’s Plan for the Modernisation and Re-equipment of British Railways was announced in 1955. The Modernisation Plan included over £100 million to be expended on signalling schemes, which would accelerate the replacement of semaphore signalling with colour-lights and track circuiting, to allow faster train services. It would include, among a myriad of other schemes, electrification and resignalling of the West Coast Main Line from London to Crewe, Liverpool and Manchester and further extension of the Southern Region’s electrified lines. Also, within ten years, steam locomotives would disappear from British Railways, to be replaced by either diesel or electric traction (BR’s last steam-hauled train actually ran in August 1968). An important technological advance around 1960 was the appearance of electronics, initially used for the remote control of signalling interlockings over distances beyond which individual signalling cables, with a separate pair of wires for each individual function, became prohibitively expensive. Systems of this type based on telephone exchange technology had been in use for many years in CTC (Centralised Traffic Control) schemes in the British Commonwealth and the USA, but their slow speed of operation and response made them unsuitable for main line railway use. What was required was a method of exchanging controls and indications between a controlling signal box and a remote site instantly, or at least within no more than a second, over a single pair of wires. The first such system, using transistors, was brought into use on the Crewe to Manchester line in 1959, where a number of ‘satellite’ relay interlockings were supervised by electronic remote control from new signal boxes at Sandbach and Wilmslow. Once such systems had become available and reliable, it would be possible to extend control areas almost without limit so that the area under the supervision of a single signal box became more an issue of operational preference than technology.



After 1945, nothing really changed for the first year or so but then mothballed schemes were started up again and completed. But with the companies exhausted from six years of war and misuse, the whole system was run-down and in need of serious repair and investment, which would come only as a result of drastic change. On Nationalisation Day, 1st January 1948, custody of the Big Four railway companies passed to the British Transport Commission (BTC) and British Railways was born. On the signalling front, the pattern of British railway signalling practice and principles was pretty well established by the 1950s. New signalling schemes using relay interlockings and control panel operation were accepted as the



Figure 9: Glass-enclosed (‘fish tank’) signalling relays



17



The other principal technical advance at this time (broadly 1955 to 1965) was that of Miniaturisation. In 1958 the IRSE had set up a Miniaturisation Committee to consider the requirements and characteristics of signalling relays. In the previous 20 years, signalling relay design had progressed from large, individually wired shelf-mounted relays (‘fish tanks’) to plug-in units where exchange of a relay required no wires to be disconnected. Size was still a problem, however, and with the advent of the new electronic technologies, the size of relays and the room needed to accommodate them was becoming a serious consideration. The IRSE Committee reported in 1963 and recommended adoption of a standard range of what are now called ‘miniature signalling relays’. IRSE miniature relays (or as they became known from the series of BR Specifications detailing their construction and functionality, ‘BR 930 relays’), became one of the most widely used signalling relays of all time so that, even in these days of electronics, they are still in use in their tens of thousands.



SSI, although remarkably ‘low-tech’ by comparison with current computer technology, has been an outstanding success. Developed under a three-way agreement between BR, Westinghouse (now Invensys Rail) and GEC-General Signal (now Alstom), it is the nearest thing there has ever been to a standardised British signalling interlocking. Numerous SSI installations have been commissioned throughout the BR network since 1985 and it has been successfully sold to a number of overseas railways. SSI interlockings can be controlled from either ‘Entrance-Exit’ control panels, or from screen-based workstations on which a mouse or trackerball is used to point-and-click on symbols representing the physical buttons or switches.



Alongside the miniaturisation of relays, signalling suppliers devoted considerable ingenuity to reducing the size of control panel components so as to allow ever-expanding signal box control areas to be represented on control panels of a practical size. Manufacturers produced ‘modular’ or ‘mosaic’ control panels in which standardised components were assembled on to square or rectangular tiles which then plugged into a baseframe structure.



22 New Interlockings We have already seen something of the origins of relay interlocking and control panels, and the 1955 BR Modernisation Plan envisaged a huge expansion of colourlight signalling and control panel signal-boxes. Faced with a shortage of signalling interlocking circuit designers, manufacturers developed ‘Geographical’ interlocking systems in which pre-wired and machine-tested packages of relays controlling individual signals and points are connected together by multi-core cables to provide the interlocking functions required for any track layout. The last 30 years have seen an explosion of electronics into all walks of life. Railway signal engineers, by nature conservative folk, have been slow to adopt electronic technology for safety-critical systems but communications, information systems, remote control and ‘human-machine interfaces’ (i.e. control panels) have all incorporated electronics to great advantage. The most dramatic advance on Britain’s railways in the recent past has been the adoption of processor-based interlocking systems. These had been used in Continental Europe for many years, but in 1985 there were still none on the BR network. In September of that year, however, the first Solid State Interlocking (SSI) was commissioned at Leamington Spa and Britain’s railways entered the age of the safety-critical processor.



Figure 10: Workstation at a BR Integrated Electronic Control Centre (IECC) In the eyes of many signal engineers, SSI is still the system of choice. Attempts to introduce other processor-based systems on to the British railway network from Continental Europe have so far met with only limited success, their suppliers having encountered problems not only with assurance and acceptance of the equipment, but also with the configuration changes required to adapt non-British systems to British signalling principles and operating practices. Another staple component of Continental signalling practice, the axle counter method of train detection, is now being widely adopted by Network Rail. Unlike track circuiting, which uses an electric current in the rails to continuously detect the presence of a train’s wheels and axles on a section of line, an axle counter works by indicating a section as Occupied when it detects and counts the passage of a train’s wheels into the section. It sets the section to ‘Clear’ again only when it detects the same number of wheels leaving, in much the same way as signalmen operating Absolute Block observe and record the entry of a train into a section, and its subsequent departure. Which brings us neatly back to the ‘Bobby’.



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23 The Future



Acknowledgements



In an earlier section I mentioned the European Rail Traffic Management System or ERTMS. In April 2006 the Railways (Interoperability) Regulations came into force, mandating implementation of a standardised signalling and train control system in line with the EU Interoperability Directive. A brief consideration of Eurostar will show why this is a sound idea – at present a train travelling from St Pancras to Brussels requires three different signalling systems, two for France and one for Belgium (until the dedicated High Speed Link to St Pancras was opened in 2007 this included AWS and TPWS for running over Network Rail’s lines into Waterloo).



The author would like to thank the many friends and colleagues from main line, metro and heritage railways who have knowingly or unknowingly contributed to this paper during his 40 years of working in signalling, and to Lloyd’s Register Rail Ltd for this opportunity to present what I hope you will find a stimulating introduction to the subject. I would also like to acknowledge the help of the Institution of Railway Signal Engineers, from several of whose publications I have extracted facts, figures and photographs, in particular Figures 4, 5, 6, 7 and 10.



These Regulations do not require retrospective compliance, so installation of ERTMS on the High Speed rail routes defined in the legislation will take place only when the existing signalling systems are replaced. In the meantime, however, a trial installation has been placed into service on the Cambrian Coast line in North Wales, between Shrewsbury, Aberystwyth and Pwllheli. The term ‘ERTMS’ is a collective name for the combination of the ‘European Train Control System’ or ETCS (which provides the ‘interlocking’ part of the signalling) with GSM-R, the standardised mobile radio communication system for railways. The system installed on the Cambrian Coast is ERTMS Level 2, which provides continuous communication between the interlocking (located at the Control Centre) and the train via GSM-R radio. Additional communication between fixed points on the track and the train provides position references and direction information by means of groups of transponders or ‘balises’. Train detection is by means of axle counters, and trains additionally report their position back to the control centre, based on the distance travelled since passing the last balise. There are no lineside signals, permission for the driver to proceed (the ‘Movement Authority’) being transmitted by radio, based on the train’s own position, that of the train or trains ahead, the correct setting of points and the permitted speed. Today’s driver of an ERTMS-equipped train on the Cambrian Coast line can therefore watch speed, distance and movement authority being displayed on a screen in the cab and control the train confident in the envelope of protection that the signalling system is providing, which will brake the train to a stop if any of these are exceeded. At the time of writing, plans are being developed to install ERTMS Level 2 signalling throughout the Great Western Main Line from London Paddington to Bristol and the West of England, the supervision of which will be concentrated in one Control Centre. So ends, for the time being, the 180-year journey that started on a wet September day on the Liverpool and Manchester Railway, where the driver crosses his fingers and peers through the gloom and the pouring rain to catch a glimpse of the bobby’s hand signal.



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Preamble and Forethoughts



A History of Railway Signalling ‘from the Bobby to the Balise’



Railway Signalling and Control is a complex and absorbing subject, with a history stretching back to the dawn of the Railway Age 180 years ago. This presentation, and the accompanying paper in the Course Book, is a personal view of that history, as Britain’s railways and their technologies have developed since 1830.



Signalling history can be divided into three periods of (very approximately) 60 years: • from 1830 to 1890 – evolution and adoption of the basic requirements for safe operation. • from 1890 until after the Second World War – development of new electrical signalling technology and principles. • from the 1950s to the present – electronics, computers and the evolution of new methods of signalling.



Stephen Clark Principal Consultant 21 May 2012



This presentation is therefore a gallop, or at least a quick trot, through that history.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



What is Railway Signalling all about?



What is Railway Signalling all about?



For the 21st century railway, signalling means:



For the 21st century railway, signalling means:



• A system of protection for rail traffic, based on: • Safe separation of moving trains. • Prevention of conflicts between trains at junctions. • Prevention of conflicts between trains and infrastructure.



• A system of protection for rail traffic, based on: • Safe separation of moving trains. • Prevention of conflicts between trains at junctions. • Prevention of conflicts between trains and infrastructure.



• A system of control to provide information to drivers by means of: • lineside signals and signs. • route indicators. • in-cab information.



• A system of control to provide information to drivers by means of: • lineside signals and signs. • route indicators. • in-cab information.



• A system of supervision to enable operators to: • direct and route trains to their destinations. • re-route and divert trains to mitigate the effects of disruptions. • deliver train services in accordance with a published timetable.



• A system of supervision to enable operators to: • direct and route trains to their destinations. • re-route and divert trains to mitigate the effects of disruptions. • deliver train services in accordance with a published timetable.



• A system of management to: • allow maximum use of the railway’s capacity.



• A system of management to: • allow maximum use of the railway’s capacity.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



The Origins of Signalling – Keeping Trains Apart



The Origins of Signalling – Keeping Trains Apart



For those of us used to driving cars, we know how far it takes to stop in an emergency.



But for the driver of an early steam locomotive, stopping in an emergency was an entirely different situation.



The Highway Code tells us, for a typical car, with an alert driver, on a dry road . . . At 50 mph . . . if an obstruction is sighted here . . .



15m (reaction distance)



your car stops here



38m (braking distance)



53m



This shows typical braking performance for a modern car with efficient and wellmaintained brakes and tyres in good condition – in railway terminology, we can ‘drive on sight’. And remember - the action of braking, once you have reacted, requires you only to move your foot from the accelerator pedal to the brake.



Not only are the laws of physics different . . . • the coefficient of friction between a metal wheel and a metal rail (typically 0.3 or less) is much lower than a rubber tyre on an asphalt road. . . . but the physical act of braking an early steam-hauled train required the driver to: • whistle to tell the guard at the back of the train that brakes were required. • close the regulator. • apply the locomotive brakes (usually a hand-wheel and screw). • apply sand to the rails to increase adhesion. • often, reverse the valve gear, and • open the regulator to apply still more braking effort . . . • . . . and keep his fingers crossed.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



20



The Origins of Signalling – Keeping Trains Apart



The Origins of Signalling – Keeping Trains Apart



Consequently, when the driver has done everything required to ‘bring his train under control’, the stopping distances look very different to those for a car . . . At 50 mph (22m/s) . . .



if an obstruction is sighted here . . .



>100m (5s) for reaction and brake application)



the train stops here



1000 - 1500m braking distance



up to 1500m



For a train that takes nearly a mile to stop, ‘driving on sight’ is clearly not an option. And - although train braking is the concern of the rolling stock engineer, not the signal engineer, no signalling system can ensure safe operation of the railway unless trains have effective brakes.



The railway is divided into a number of ‘Block Sections’ and only one train is permitted to enter a Block Section at a time. In the 1830s, the only practical way to enforce the Block system was by means of a minimum time interval.



The system was operated by the railway’s own policemen (‘Bobbies’) at the lineside, giving hand signals to trains and timing them with a sandglass. But Time Interval working could not give an ‘absolute’ assurance that a block section was unoccupied before a following train was allowed to enter it.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



The Origins of Signalling – Keeping Trains Apart



The Origins of Signalling – Keeping Trains Apart



From the 1850s, Electric Telegraphs allowed messages to be exchanged between signalmen so they would know when it was safe to allow a train to proceed.



The Three-Position Block Telegraph Instrument shown here simplified operation by providing for one of three standard messages to be sent: • ‘Line Clear’ • ‘Train On Line’ • ‘Line Blocked’ (the normal state, with no trains in or approaching the section)



Early telegraph instruments were slow and cumbersome to use. Messages had to be spelt out, letter by letter.



These instruments provide the basis of a safe method of signalling that is in use to this day.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



The Origins of Signalling – Keeping Trains Apart



The Origins of Signalling – Keeping Trains Apart From the 1840s, fixed signals started to be used, instead of the Bobbies’ hand signals, to convey instructions to train drivers.



A word about Accidents . . . We are used today to the idea of ‘engineering for safety’. But with no experience on which to draw, evolution of safety was slow and reactive. Accidents were the major incentive for change.



These took a number of different forms, ranging from the Great Western Railway’s rotating Disc and Crossbar signal . . .



Anyone interested in the history of signalling should read ‘Red For Danger’ by L. T. C. Rolt, first published in 1955 but updated since.



. . . to various types of semaphore signals with moveable arms. As with the Block Telegraph instruments, many signals of this type remain in use.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



21



The Origins of Signalling – Keeping Trains Apart



The Origins of Signalling – Keeping Trains Apart



After 1860, the next significant step in the evolution of British signalling was the development of Interlocking. Interlocking is required to ensure that a signalman operates points and signals such that unsafe train movements are prevented, for example: • signals controlling movements that conflict at a set of points • signals controlling movements that directly ‘oppose’ other movements (i.e. that lead to a head-on collision) • showing a signal allowing a driver to proceed with points incorrectly set. Interlocking of points and signals is achieved by interconnecting the levers controlling them through a mechanism that will allow only certain combinations of levers to be operated, or to ensure that operation takes place in a safe sequence.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



The Origins of Signalling – Keeping Trains Apart



Signalling - the March of Technology



This picture shows a typical Lever Frame as it would have been supplied from the manufacturer’s works.



During the last quarter of the 19th century there was a flourishing of technical invention and innovation, including: • train detection systems – track circuits and treadles to assist safe operation; • ‘enhanced’ block systems – interlinking of signal levers with the block instruments to enforce safe and sequential operation; • improved control of single-line working;



Floor level



and, in the last few months of 1899: • Britain’s first installation of power-operated signalling



Interlocking mechanism



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



Signalling - the March of Technology



Signalling - the March of Technology Power signalling opened the way for colour light signals to start replacing mechanical semaphores.



With power operation, the signalman was operating only valves or switches to move points and signals, so the levers controlling them could be miniaturised.



Use of colour-light signals, together with continuous track circuiting to detect the presence of trains, allowed long stretches of railway to be controlled automatically . . .



Glasgow Central signalbox (installed in 1907, replaced in 1960) with 374 mechanically-interlocked miniature levers.



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



22



Maximising line capacity



Signalling - the March of Technology Power signalling opened the way for colour light signals to start replacing mechanical semaphores.



Coulsdon North Cane Hill Quarry Worstead Green Earlswood Earlswood Station Salfords Horley North Horley South Gatwick Tinsley Green Three Bridges North Three Bridges Three Bridges South Balcombe Tunnel Balcombe Intermediate Balcombe Station Stone Hall Copyhold Jn Haywards Heath North Haywards Heath Folly Hill Wivelsfield The 36 signal boxes previously required Keymer Jn Burgess Hill Lovers Walk for normal operation were reduced to Hassocks Brighton North only 8, located at the junctions. Clayton Cutting Brighton South A further 9 signal boxes could be ‘opened Brapool Cutting Brighton West Patcham when required’, but normally their signals New England Preston Park Holland Road would work automatically.



from London



Use of colour-light signals, together with continuous track circuiting to detect the presence of trains, allowed long stretches of railway to be controlled automatically . . .



The use of colour-light signals spaced at regular intervals, worked automatically wherever possible, allowed maximum use to be made of a line’s capacity without the need for large numbers of individual signalboxes and their associated ‘bobbies’. c. 1km



c. 1km



c. 1km



c. 1km



Train 1



Resignalling from Coulsdon to Brighton – 1932 covering 36 route miles



BRIGHTON



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



Maximising line capacity



Maximising line capacity



The use of colour-light signals spaced at regular intervals, worked automatically wherever possible, allowed maximum use to be made of a line’s capacity without the need for large numbers of individual signalboxes and their associated ‘bobbies’. c. 1km



c. 1km



c. 1km



The use of colour-light signals spaced at regular intervals, worked automatically wherever possible, allowed maximum use to be made of a line’s capacity without the need for large numbers of individual signalboxes and their associated ‘bobbies’. c. 1km



c. 1km



c. 1km



c. 1km



Train 1



Train 1



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



Maximising line capacity



Signalling – maximising line capacity



The use of colour-light signals spaced at regular intervals, worked automatically wherever possible, allowed maximum use to be made of a line’s capacity without the need for large numbers of individual signalboxes and their associated ‘bobbies’. c. 1km



c. 1km



c. 1km



c. 1km



The use of colour-light signals spaced at regular intervals, worked automatically wherever possible, allowed maximum use to be made of a line’s capacity without the need for large numbers of individual signalboxes and their associated ‘bobbies’.



c. 1km



Train 1



c. 1km



Train 2



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



c. 1km



c. 1km



c. 1km



Train 1



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Modern developments



Modern developments



The use of colour-light signals spaced at regular intervals, worked automatically wherever possible, allowed maximum use to be made of a line’s capacity without the need for large numbers of individual signalboxes and their associated ‘bobbies’. c. 1km



c. 1km



Train 2



c. 1km



. . . from miniature levers to control panels in the 1950s . . .



c. 1km



Train 1



This method of operation, which is known as ‘Track Circuit Block’, using multipleaspect colour-light signals controlled by a system of train detection, remains the standard signalling architecture on British main lines. In the meantime, however, the technology of the signalbox itself has continued to evolve . . .



A History of Railway Signalling



A History of Railway Signalling



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LLOYD’S REGISTER RAIL



Modern developments



Modern developments



. . . to very large control panels in ‘Area Signalling Centres’ in the 1970s and 1980s. . .



. . . to VDU screens and computer-based interlockings in the late 1980s and 1990s.



A History of Railway Signalling



A History of Railway Signalling



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LLOYD’S REGISTER RAIL



Other signalling developments



Other signalling developments



In addition to the development of signals, interlockings and control systems, the last third of the 180-year history of signalling has seen the appearance of a number of important technical improvements.



The most recent – and significant – development is the successful commissioning of a trial ‘European Railway Traffic Management System’ (ERTMS) on the Cambrian Coast line from Shrewsbury to Aberystwyth and Pwllheli.



• Automatic Warning System (AWS) – to remind a driver that the next signal ahead is not showing a ‘Proceed’ (Green) aspect and that action is required to prepare to stop.



With ERTMS Level 2 a Movement Authority (MA) for a train to proceed is transmitted from the Interlocking to the train by radio and displayed in the cab – the driver then controls the train in accordance with this authority (permitted speed, distance to go).



• Train Protection & Warning System (TPWS) – to bring a train to a stand if it passes, or appears likely to pass, a signal showing a Red (Danger) aspect.



• If the driver exceeds the MA, the system will intervene and the train will be braked.



• Axle counters – train detection irrespective of track condition, adverse weather, or railhead contamination.



• No lineside signals are required, only fixed markers. • Train detection is by means of axle counters, connected to the Interlocking. • Position references are given by ‘balises’ (transponders) mounted on the track.



A History of Railway Signalling



A History of Railway Signalling



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LLOYD’S REGISTER RAIL



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Future signalling developments



A History of Railway Signalling



What next . . .



That may well be up to some of you here today!



Thank you for listening!



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



A History of Railway Signalling Acknowledgments: • To the Institution of Railway Signal Engineers, for inspiration, facilities and photographs • To colleagues in Lloyd’s Register Rail, for support and encouragement



For more information, please contact:



• To Siemens Transportation, Invensys Rail Ltd and Mark Glover, for photographs • To Jim Dapré, for the photograph on the title slide



Lloyd’s Register Rail Ltd 71 Fenchurch Street London, EC3M 4BS T +44 (0)20 7423 2943 F +44 (0)20 7600 1441 E [email protected]



A History of Railway Signalling



A History of Railway Signalling



LLOYD’S REGISTER RAIL



LLOYD’S REGISTER RAIL



The Lloyd’s Register Group works to enhance safety and approve assets and systems at sea, on land and in the air – because life matters.



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