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- Herausgeber: Crowood
- Kategorie: Lebensstil
- Sprache: Englisch
The characteristic landscape of the Lake District is influenced by its geology. The huge array of different rocks found there determines the shape and appearance of the fells and dales. Also, as the dominant building material in the region, rocks impact both the local architecture and the economy through quarrying. A simple easy-to-read guide to the rocks of the English Lake District, with nearly 200 colour illustrations including diagrams, maps and photographs, this book provides an understanding of the main types of rock and characterizes over sixty of the most common rocks. It describes where to find them and how to recognise them in the landscape. Details are given of the use of rocks in local buildings and how the rocks are still quarried today, and finally, their importance to the local economy.
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Veröffentlichungsjahr: 2019
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COLOUR LIGHT SIGNALLING
FOR MODEL RAILWAYS
An offset post-mounted signal and ground-mounted signal on Blackburn MRC’s OO layout ‘Blackmill’.ANDY YORK – BRM
COLOUR LIGHT SIGNALLING
FOR MODEL RAILWAYS
SIMON PALEY
First published in 2019 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR
www.crowood.com
This e-book first published in 2019
© Simon Paley 2019
All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.
British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.
ISBN 978 1 78500 626 5
CONTENTS
ACKNOWLEDGEMENTS
I would like to thank my friends, family and colleagues for the support they have shown over the months I have been writing this book. Special thanks go to the signalling designers in the NR Reading design office, who have been invaluable in giving technical advice and examples, as well as to the staff and management of Network Rail for encouraging this book.
My thanks also go to all those who have provided proofreading services and photos. All photos are copyright of the author, unless cited otherwise.
All the diagrams in this book have been created by the author and are not to scale. However, mostly they are based on diagrams available on the Railway Group Standards website (https://www.rssb.co.uk/railway-group-standards). The symbols used for layout diagrams can be found in figure 3 in Chapter 1.
All information at the time of writing (December 2018) is correct to the best of my knowledge and any opinions/views expressed in this book are entirely my own.
CHAPTER ONE
INTRODUCTION
Signalling is one of the main systems – some might argue the main system – that make the nation’s railways tick. Whilst a railway could feasibly be run without signalling (or indeed run without care for the rules of signalling), as was demonstrated in the early years of the railways, this would be fraught with danger. Signalling failures have cost hundreds of lives over the 190 years or so of the history of the railways. So, if the system is so critical to the operation of the railway in real life, why is it that a lot of model railway owners and builders seem so lacklustre in the provision of it in their miniature worlds?
Simply, it is because signalling can be highly complex, regionalized and era-specific. This means that every region and timescale has a different approach to signalling design and operation. For the average railway modeller, who is generally building a model railway created within their imagination without a specific location in mind, this makes it a painstaking task to piece together the makings of a miniature signalling system that matches their chosen track layout, area and period of operation.
Over the past fifty years, this task has been reduced for modellers of the ‘modern image’ epoch, the time when diesel and electric traction took over the railway from steam, with the widespread use of colour light, and later in-cab, signalling systems. This has brought with it a degree of standardization, meaning that now the changes in area and era are less pronounced, simplifying the process to identify the components needed for the modeller to create their model system. In the model world, the introduction of colour light signals makes modelling the system easier, particularly with the advancement of light-emitting diode (LED) technology, as there is no longer the requirement for intricate mechanisms, and the associated problems of scaling these down, that are present with mechanical signalling.
Fig. 1 People say ‘colour light signalling is simple’, and it can be, until you start looking at something like this … the eastern approach to London Bridge Station.
However, there is still a factor with colour light signalling that makes it hard for the modeller to achieve a prototypical recreation. With the advent of colour lights also came route relay interlockings, followed by solid-state, or computer-based, interlockings as replacements for mechanical interlocking. With this, the possibilities for technological progress was far greater, so elements kept being added to already complex systems to make them highly sophisticated and nowadays even intelligent.
All this has led to the initially simple and standardized colour light system becoming just as bespoke as semaphore signalling. Whilst there have been books for railway modellers in the past covering colour light signalling, these usually describe the use of semaphore signals while covering colour lights in a chapter or two, using the same principles and based on a handful of diagrams dating back to the 1980s from British Rail. Colour light signalling has grown to be so diverse and interesting that it is now time for a book dedicated to modern railway signalling; this is that book.
The aim of this book, which has been written by a railway modeller and professional signalling designer and peer-reviewed by experienced signalling designers, is for it to be used as a handbook for those railway modellers wishing to install a model colour light or in-cab signalling system on to their model railway, either as a retrofit to an existing layout, or as part of the process of building a layout from scratch. Real-life standards, prototypical practice and design principles will be followed.
Fig. 2 Model colour light signalling on Blackburn MRC’s layout ‘Blackmill’.ANDY YORK – BRM
This book will provide the tools to help the average railway modeller to design the signalling for their layout with confidence. These tools include chapters that cover a brief history of colour light signalling and track design influences. It will then go on to describe the different types of signals that are used in the UK, explaining the hard and fast rules for the use and positioning of these signals. The advantage of colour light signalling is that the basic positioning and usage rules have remained the same, albeit with regional or area-specific differences relating to the combinations of aspect and indications.
THE SCOPE OF A SIGNALLING SYSTEM
The primary role of a railway signalling system is the safe control of trains on the railway network through the provision of clear indications to train drivers that are easy to understand, interpret and act upon. This role is divided into two separate categories – indirect train speed control and train separation. In terms of indirect train speed control, the UK’s signalling principles have almost exclusively been route-based signalling, rather than the speed-based signalling used on the Continent. With route-based signalling, the signalling provides information on the route a train is to take and it is the driver, through his route knowledge, who controls the speed of the train. However, with the increasing use of in-cab signalling, the UK’s signalling principles are changing to speed-based signalling, where the signalling provides speed information directly to the driver, without route information.
In terms of train separation, the signalling system’s purpose is to provide the correct degree of separation between trains for the given line speed and then maintain it for as long as needed. This is to stop trains travelling too close together and to provide a ‘buffer zone’ in which trains can be brought to a stand without the risk of colliding with another train. A secondary purpose of signalling systems is to give line controllers and signallers a visual indication of where any particular train is at any specific time through the use of the train detection systems.
The scope of a signalling system for a model railway is much more limited, in that it is not seen by many as a control system but as an aesthetically pleasing addition to a layout. There are some people who add signals to their layouts so that they can operate it prototypically, but most crave visual realism.
Fig. 3 Symbols used for layout diagrams.
CHAPTER TWO
A BRIEF HISTORY OF COLOUR LIGHT SIGNALLING
Sadly, the history of colour light signals and signalling in general is the history of injuries and fatalities on the railway, as a lot of the innovations in the signalling world have resulted from lessons learnt from accidents and incidents. It is these events that have seen more than 600 people killed and over 2,000 people injured since 1825 as a direct result of either a signalling failure or a Signal Passed at Danger (SPAD) incident (according to statistics released by the Office of Rail and Road in 2015 ). More information on how accidents have influenced railway and signalling innovations can be found in Tom Rolt’s Red for Danger (1955). Most of the history in this section has been referenced from and based upon the book A Chronology of Railway Signalling 1825–2018 by Peter Woodbridge (2018), a thoroughly researched and interesting book.
The development of railway semaphore signalling has already been well documented in many books and websites, so will not be covered in this book. However, it should be noted that semaphore signalling and colour light signalling have coinhabited the nation’s railways for the last 100 years and continue to do so, whilst most types of ‘block working’ that are usually associated with semaphore and mechanical signalling are still being employed using colour light signals. In fact, seeChapter 6 for a way in which colour light signals and semaphore signals could be combined.
Although this book will not cover the history of semaphore signals, a basic history of signalling before colour light signalling was introduced will be instructive. When the Liverpool & Manchester Railway, the first public passenger railway, opened in September 1830, it took three years before a form of ‘signalling’ first appeared. This consisted of policemen who positioned their arms to provide an indication of the line ahead. A further three years saw the introduction of what is believed to be the first fixed railway signal (a red and white pivoted chequered board), created for the Liverpool & Manchester by E. Wood, although it was not until 1838 that a railway had signals from opening. These were installed on the Grand Junction Railway from Birmingham to Warrington and used red and green lamps, which were hoisted up a post and used covers over the lamps to show information to the drivers. It is thought that this could be the first regular use of the terms ‘OFF’ and ‘ON’:
• ‘OFF’ for a signal showing proceed
• ‘ON’ for a signal showing danger.
In the intervening years, the electric telegraph was invented in New York by Samuel Morse. It was this, albeit in a refined form, that allowed signallers to talk to each other and create a signalling ‘system’, but this needed to be housed somewhere. This need was partially answered in 1839 when what could be called the first ‘signal box’ was installed between London Bridge and New Cross. It consisted of a simple hut containing a wooden stage with levers mounted on it.
Just a year after the first signal box was installed, the Victorians invented the first in-cab signal. Normally considered to be a highly modern invention, this in-cab signal was a system to sound a loco’s whistle and rotate a lamp when the train passed a signal, but it was operated by the lever of a lineside signal. In this respect, it could be considered the precursor to the modern European Train Control System (ETCS) overlay! It was not continued, although different techniques were tried out in the years up to the 1900s.
The fixed signal telegraph system (which also led to the invention of the block operating principle) and signal box continued to be developed throughout the 1800s, until 12 June 1889 when a collision in Armagh in Northern Ireland killed 80 and injured 260. This prompted the signing into law of the Regulation of Railways Act 1889 just seventynine days later. This law, commonly known amongst railway engineers as the ‘lock, block and brake law’, required all passenger lines to have: a Facing Point Lock (FPL) on facing points, an interlocking, block working between signal boxes and all trains to be fitted with a brake that would automatically be applied if a train divided. All this equipment had already been invented (the FPL in 1866, the interlocking in 1843, block working in 1852 and automatic brake in 1869) and was in use in varying degrees of importance across the railways. However, it was the ‘lock, block and brake’ law that enforced their use without exception and started the path towards the signalling systems we know today.
Another fundamental part of the modern colour light signalling system, the track circuit, was invented in 1872 by Dr William Robinson in Brooklyn, New York, although this was based on similar devices concocted in 1848 and 1860. The first track circuits in the UK were installed experimentally in London at St Paul’s in 1886, with the first successful use in the Gasworks Tunnel in King’s Cross in 1894. A track circuit works by an electrical supply being fed into the rails at one end of a track circuit section and energizing a track relay connected to the rails at the other end of the section (the actual location of this relay tends to be in a relay room, but it is the same principle). Should a train enter the section, the axles (assuming that the electrical resistance of the axle is lower than that of the rails) cause the electrical circuit to ‘short’. This de-energizes the track relay, causing the section to show ‘occupied’.
Fig. 4 These models of Eastern Region searchlight signals are on the Model Railway Club’s ‘Minories (GN)’ EM gauge layout set in the BR Blue era and based on the famous Cyril Freezer track plan of the same name.ANDY YORK – BRM
Another basic part of the modern system, a point driven by an electric motor, was installed in the USA in Ohio in 1889, it being a further nine years before the first UK installation. The next development towards colour light signalling was the first installation of what would become Track Circuit Block (TCB), the basic operational principle of the majority of lines equipped with colour lights. In 1901, the first TCB installation controlled pneumatically operated semaphore signalling on the Andover Junction to Grateley section of the London & South Western Railways network.
Fig. 5 A searchlight signal at Nottingham. Although the rest of the station at this time was standard heads, this signal was a searchlight for sighting reasons.MIKE ROMANS
The first use of a signal consisting of only coloured lights in the UK was on the Liverpool Overhead Railway (LOR) in 1920. This took the form of two-aspect signals that used a ‘searchlight’ mechanism invented in the USA. The LOR system was automated using AC track circuits (installed first on the Metropolitan & District Railway in London in 1903) and extended across the system.
What could be considered the first ‘power signal box’ was, rather surprisingly, created in 1921 at Quainton Road on the joint Great Central & Metropolitan Railway near Aylesbury. Although not a true power signal box, it was the first signal box to control fully a stretch of railway, in this case a double junction using point motors and solenoid semaphore signals, just under half a mile away (721yd to be exact). This was considered incredible, seeing as the longest ‘pull’ (the distance between the lever in the signal box and the piece of equipment controlled by it) in the UK was for a single distant signal at roughly the same distance. Operation of points was limited to just 350yd on passenger lines (further on freight lines or for those points worked by wires).
The first use of the term ‘three-aspect signalling’ was in a 1922 report by the Three-Aspect Signalling Committee of the Institute of Railway Signal Engineers (IRSE). The report not only recommended the adoption of the term over ‘three-position signalling’, but also recommended that signals required to display all three aspects (green for proceed, yellow for caution and red for danger) should be colour light signals rather than three-position semaphore signals. Also, rather ironically given its name, the committee recommended a fourth aspect: double yellow, now known as preliminary caution.
In the following year, the first stretch of UK railway to be controlled solely by three-aspect colour light signalling was commissioned between London Marylebone and Neasden on the then new London & North Eastern Railway (LNER) (formerly the Great Central Railway). This used a mixture of searchlight and multi-aperture signals and was installed to allow close three-minute headways so that the railway could successfully convey crowds for the 1924 British Empire Exhibition at Wembley. This installation lasted until 1989, before being replaced by the Western Region of British Rail after a number of problems resulting from years of maintenance cutbacks by the London Midland Region anticipating the line’s closure.
Fig. 6 A colour light signal on a layout called ‘Up the Junction’. It is often forgotten how early colour lights came in, shown here by the early green livery of BR’s Southern Region.MIKE LYNCH
The first use of the fourth double yellow aspect was between Holborn Viaduct and Elephant & Castle on the Southern Railway in 1926. This took a different form to the now standard head (introduced in 1937), with the aspects from the top being green followed by yellow, red and the second yellow at the bottom. Both this type and the current form of four-aspect signal use the principle of separating the two yellow aspects, as putting the two yellows next to each other could cause them to be merged when seen from afar and be confused for a single yellow. While this would be termed safer, it resulted in drivers slowing their trains earlier than necessary, thereby increasing headway and removing an advantage of the fourth aspect.
By this time, all but one of the ‘Big Four’ railway companies now had some form of colour light signalling on their networks. The exception was the Great Western Railway (GWR), which took until 1931 to install colour light signals between Paddington and Southall to replace semaphore signals, although these were still controlled using absolute block and lever frames.
Meanwhile, two years earlier the LNER had installed the first control panel and relay interlocking at Goole Swing Bridge, the equipment being an Individual Function Switch (IFS) panel and interlocking manufactured by the famous Westinghouse Brake and Signal Company. However, the first true relay-based interlocking was installed in 1932 at Wood Green on the Piccadilly Line, which also introduced the concept of Automatic Route Setting (ARS).
Then came a total swing in the principles of signalling in the UK, in the form of lineside speed signalling. This concept, which differed from the previous (and current, almost) practice of route signalling, was developed in the UK by A.E. Bound on a section of the London, Midland & Scottish Railway (LMS) between Heaton Lodge Junction and Thornhill Junction in 1933. This utilized searchlight signal heads showing combinations of aspects to specify a speed to the driver. This system did also include routing information, but was primarily a speed signalling installation. A second scheme was installed on the Camden to Watford DC Lines, but both schemes were ultimately replaced with conventional route signalling.
Fig. 7 An image showing the speed signalling at Mirfield, c.1970.MIKE ROMANS
Originally, route indications in colour light signalling were given through separate heads in the same fashion as route information was conveyed in semaphore signalling. However, with the colour lights being brighter, if a signal had several heads for several routes, the aspects would simply merge when viewed from a distance, making it very difficult to pick out the route set until the train was on top of the signal. This problem was partially solved by LNER engineer A.E. Tattersall, who devised the ‘direction indicator’. Consisting of neon tubes arranged at vertical, 45, 90 and 135 degrees to the left or right, these (first installed at Northallerton in 1934) initially shone with a red light, which was not much better than before. However, these were soon modified to a series of five white lights without a vertical arrangement and the junction indicator, or ‘feather’, was born. There were brief trials in 1985 at Crewe and 1994 in Exeter to use a fibre-optic bar and a blue ‘pivot’ light respectively, but these were not continued.
Also installed at Northallerton along with direction indicators were the first position light signals. These signals consisted of three lights arranged in a triangular formation. When ‘ON’, two white lights horizontally were shown, whilst when ‘OFF’, the top and right lights would show white. The Railway Clearing House made the position light standard in 1934 after recommendation by the Ministry of Transport in the same year that the position light was installed. The standard form of position lights for the next fifty-six years was first used by the LMS at Crewe in 1940 (although they had been seen in Leeds during 1937, but were not standard), with a single red and a single white light displayed horizontally when at danger and two whites at 45 degrees when at proceed.
The first recorded use of co-acting ‘pig’s ears’ (seeChapter 6), three-lamp Southern junction indicators (installed by the Southern Railway/Region up until 1967 and lasting to 2006) and the multi-lamp route indicator was for the resignalling of London Waterloo ‘A’ Signal Box in 1937. Also in 1937, the first Entry–Exit (NX) panel was commissioned at Brunswick Goods Signal Box on the Cheshire Lines of the LMS. The NX panel has become synonymous with colour light signalling and is still in use in a lot of signalling centres in the UK.
INTRODUCTION OF DIFFERENT POSITION LIGHTS
The introduction of different types of position light is spread out fairly throughout signalling history: the first pre-set shunts were installed at Hull in 1938; the first ‘yellow shunt’ was installed at Crewe in 1940; the first limit of shunt in 1985; and the ‘Proceed on Sight Aspect’ (PoSA) signal in 2003.
COLOUR LIGHT SIGNALLING DURING WORLD WAR II
The development of colour light signalling slowed during World War II, but, interestingly, colour light signals had their voltage reduced during the night so that they were dimmer and complied with the blackout regulations.
The first innovation after World War II was the installation of York Signal Box in 1951. This was radical compared to previous signal boxes, in that it was the first use of a signal box where the signaller could not see any of the trains under their supervision. This was achieved through the use of a fully track-circuited layout and a train describer that would update in real time as a train travelled through the layout and would move train descriptions along the panel with the train. This sort of signal box, called the Power Signal Box (PSB), is now common across the country.
The next year an accident occurred that would see a step change in the safety systems installed on the UK’s railways. The accident was a multiple collision at Harrow & Wealdstone on 8 October 1952, when a driver missed a distant signal and subsequently passed two semaphore stop signals at danger, resulting in a rear-end collision, 112 deaths and 340 injured. It is commonly thought that this incident caused the development of AWS (Automatic Warning System), but the system was already being developed and the public and political pressure to prevent another accident meant that the programme was accelerated. The trials began in 1955, with the roll-out in 1956, although there were some freight-only lines not fitted by the time of the Train Protection and Warning System (TPWS) implementation forty-five years later (seeChapter 12).
Fig. 8 An early Southern three-lamp junction indicator fitted to WB07 at Barnes, shown in 1993.MIKE ROMANS
Fig. 9 The operating floor of Three Bridges Area Signalling Centre, which controls the line from Norwood to Brighton.
By this point, more and more relay-based interlockings were being introduced and it was in 1960 that a new type of relay interlocking was created by the Western Region. Always wanting to do something different, the Western Region installed the first prototype ‘E10k’ route relay interlocking at Birmingham Snow Hill. The E10k interlocking differs from normal route relay interlockings in that it uses relays that ‘summarize’ lots of logic statements to reduce the number of relays in a single circuit. It is considered by some, mostly of a Western Region persuasion, to be a simple and elegant system.
Fig. 10 A BR930 relay.
The next major innovation in colour light signalling was the first UK application of axle counters for train detection. This was in 1967 at Glasgow Queen Street, where it was not possible to insulate a steel bridge from a track circuit. This was one of the very few installations of axle counters in the UK up to 1999, when the whole station was provided with only axle counters as the train detection. It was after this that the widespread adoption of axle counters began. There are two basic types of axle counters – one is mechanical and the other works magnetically. The mechanical type, actually called a treadle, uses two levers that are depressed by the flanges of a wheel (the sequential operation of the levers determining the direction of travel). These were the original type of axle counter, but now the preference is for the magnetic type, with the mechanical type being commonly used for level crossings.
Fig. 11 An axle counter head (on the far running rail, just off centre to the right) and its magnetic field generator (the grey and yellow box behind the blue fencing) at Oxford.
The magnetic type is much more sophisticated than the mechanical. A magnetic field is generated around the axle counter ‘head’. If this magnetic field is disturbed by a passing train wheel (a train wheel creates a distinctive disturbance in the field compared with, say, a shovel), then a wheel is detected. There is no physical contact with this type of axle counter. To determine whether a track section is clear, the wheels are counted up (by either type of axle counter) at the start of the track section and then counted down at the end of the section. If the resulting value is zero, the section is clear; if it is anything other than zero (a negative number is possible), the section is not clear.
A crash that caused signal engineers to look carefully again at the safety of the system was the Moorgate crash on 28 February 1975, which saw a tube train collide with the end wall at the terminal platform at Moorgate, killing 43 and injuring 300. Whilst there was nothing wrong with either the train or the signalling, it resulted in British Rail changing signalling principles so that signals would only show single yellow towards a buffer stop rather than green.
Two additional aspect sequences were added in 1979 at Didcot East Junction to those that could be displayed by four-aspect signals. With the introduction of BR’s High Speed Train (HST), which could travel at 125mph, it was realized that additional warning was needed on approach to a high-speed divergent route; this system is called ‘Main Aspect approach controlled from Yellow with Flashing Aspects’. or MAY-FA (seeChapter 8). These aspects are flashing cautionary aspects, both single and double, and through their use the speed of the train is reduced using caution and preliminary caution aspects and the driver is given a warning of a change in route through the flashing.
The first foray into the computer age for the signalling engineer was the implementation in 1984 of Radio Electronic Tokenless Block (RETB; seeChapter 10) on the Far North Line in Scotland. This was the first use of Solid State Interlocking (SSI) equipment before the pilot installation of true SSI for signalled layouts (RETB being effectively unsignalled) at Leamington Spa in 1985, although a form of SSI was installed on the Henley Branch in the 1960s. The same year also saw the introduction of fibre-optic technology for route indicators at Crewe.
In 1987, a further flashing aspect was added to signals on the East Coast Main Line (ECML) between Peterborough and Stoke Tunnel, as part of the introduction of 140mph test trains for the new Class 91 electric locomotives. The distance between a preliminary caution and danger aspect was not considered to be long enough to bring the train to a stand safely, so a flashing green aspect was introduced, which permitted these test trains to travel at 140mph, while a steady green aspect meant a reduction in speed to 125mph.
Probably the biggest change for the signalling engineer was not just in the equipment they would use, but the way in which S&T staff across the industry worked (note that S&T currently stands for Signalling & Telecommunications, but used to refer to Signalling & Telegraph before the telephone overtook telegraphic communications). This change came about as a result of the Clapham Junction rail disaster on 12 December 1988 (as well as a collision at Purley on 4 March 1989 and a third collision at Bellgrove in Glasgow just two days after that). The major equipment-related recommendation from the resulting report was the implementation of Automatic Train Protection (ATP), as well as all trains being fitted with radio communication. The crash report, The Hidden Report, also recommended the introduction of a competency recording system, later to become the IRSE Licensing Scheme, as well as design, testing and installation handbooks, signalling testing courses and the enforcement of drugs and alcohol policies.
Fig. 12 The VDU displays controlling London Bridge at Three Bridges Rail Operating Centre.
Having been brought into the digital age at Leamington with SSI, the next step was to convert to screens rather than panels. This step was taken in 1989 with the implementation of the Integrated Electronic Control Centre (IECC) at Liverpool Street in London and was the first in a series of developments of the Visual Display Unit (VDU) ‘workstations’. Although this does look like an ordinary computer, the system uses specialist equipment that can’t be hooked up to your normal Microsoft Windows! This also was the first main-line installation of ARS, although it had been in experimental use, rarely, at Three Bridges Area Signalling Centre between Haywards Heath and Balcombe Tunnel. Further IECCs were installed at York, Yoker (Glasgow), Marylebone, Tyneside, Slough, Ashford (which would later include the Channel Tunnel Rail Link), Swindon, Sandhills (Liverpool), Upminster, Edinburgh and Didcot, the latter being installed in 2010. Meanwhile, over on the Continent, the beginning of the biggest upheaval in railway signalling was being initiated, with the European Commission authorizing the development of the European Rail Traffic Management System (ERTMS) in 1989 (seeChapter 10).
Whilst it may seem that signalling kept pace with the latest technological innovations, it did lag behind in some areas. One of these areas was the adoption of the Light Emitting Diode (LED), which was originally invented in 1962, but it took until 1991 for the railway to use LEDs for signalling equipment (they had been in use as indications on panels since 1984). This was in a Driver’s Crossing Indicator (DCI, seeChapter 9) for locally monitored automatic level crossings.
Fig. 13 An LED ‘Light Engine’ (not to be confused with the general railway term to mean a locomotive working on its own). The light is emitted from the small (2× 1mm) LEDs at the centre of the lens, the little yellow rectangles. These produce enough light to be seen 800m away.
However, British Rail also managed to launch itself to the forefront of technology in 1991, with the pilot schemes for ATP. They were initially installed on the Great Western Main Line (GWML) out of Paddington and the Chiltern Main Line from Marylebone. These systems became one-off installations, intended as comparison systems prior to full roll-out, but it was decided that ATP was too costly to implement for the safety benefits it might bring. Initially on the GWML the system was not viewed as signalling, but as more of a test system. However, this was to change in 1997, after the Southall collision on 19 September. This collision, between an HST and an empty stone train, was caused in part by the isolation of the ATP system (which at that time was regarded as acceptable). After this incident, the use of ATP, where fitted, would become the normal operation. In fact, First Great Western made a pledge that all trains capable of running at 125mph would have operational ATP, the pledge adorning the side of all HST Mk3 coaches in its fleet.
In the intervening period (this was of course during the privatization of the UK rail network), British Rail and Railtrack issued a report in 1995 to the Ministry of Transport, which stated that ATP was unaffordable. The minister accepted the report only on the understanding that an alternative safety system would be developed. This system turned into the Train Protection & Warning System (TPWS, seeChapter 12). The initial trials started in 1997 between Luton and St Albans using Class 319 Electric Multiple Units (EMUs). This choice of route, Thameslink, is perhaps a little ironic, given that it was the first urban commuter line to use ETCS over TPWS as a train-protection system. The Ladbroke Grove crash in 1999 sped up the deployment of TPWS through the passing in the same year of the Railway Safety Regulations, which stated that a train-protection system for all trains must be in place, starting from January 2000, with full compliance to be met by January 2004.
The trials for the use of LEDs for signals began in the very early 2000s, starting with position light signals. These LED signals, manufactured by Dorman, used the same aspects as fibre-optic position lights introduced in 1996, with two whites at 45 degrees for ‘OFF’ and two reds horizontally for ‘ON’. This change from the ‘red-white’ filament lamp versions is said to have significantly reduced the SPADs of ground position light signals and therefore a campaign change was started in 2001. Although the campaign saw a limited number of the already rare yellow shunts converted to show two yellows when ‘ON’, the installation of new yellow shunts was banned in 2002, with only a handful remaining today.
The trial of LED signals as replacements for filament lamp main-aspect signals, again using Dorman technology, started in 2002 on the Western, with a signal each at Reading and Hayes & Harlington. The large-scale trial took place as part of the controversial West Coast Route Modernisation. Product acceptance was given in 2003, and between then and the end of 2006, 13,000 position light and 1,300 main-aspect signals were converted to LED technology. It is today the standard option for signalling equipment. Unipart Dorman was the main supplier of LED signals up until 2006, when the first Variable Message Signs Ltd (VMS) type signal was trialled at Preston, and since then the choice between the two suppliers has become almost random.
With the connection of the UK to the rest of Europe when the Channel Tunnel opened, the first in-cab signalling system landed on UK soil. This was the TVM430 system, used by the French since 1987 for their TGV lines. It was first commissioned on phase 1 of the Channel Tunnel Rail Link up to Gravesend in 2003. The system does not use lineside signals and instead uses speed-based signalling displayed to the driver via an in-cab display, although lineside markers, called repères, denote the start and end of block sections.
Fig. 14 A Signalling Solutions CBI ‘Smartlock’, which controls the area between Paddington and Hayes, at Network Rail’s Thames Valley Signalling Centre in Didcot.
In the same year, the first use of a Computer-Based Interlocking (CBI), a Siemens SIMIS-W system, was made as part of the Portsmouth resignalling. A CBI differs from an SSI, in that changes that are made to the interlocking are handled via a USB stick and uploaded from a computer, whereas SSI requires components to be physically replaced. The CBI is now quickly replacing SSI and is the preferred interlocking type in new installations.
2003 was a busy year for railway signalling in the UK as it also saw the mainstream introduction of the Preliminary Route Indicator (PRI). These had previously been used when colour light splitting distants were reintroduced to the rulebook in 1996 (although they had been permitted since 1992) and were commissioned on the approach to Heathrow Airport Junction. Between then and 2003, the PRI had been used sporadically as a local rule rather than a national implementation.
The development of railway signalling in the UK stagnated slightly after this, but then took a massive leap forward in 2010 with two important milestones. The first of these was the publishing of the Modular Signalling Handbook. This introduced the concept of modular signalling, which was intended to replicate the mechanical signalling in colour light form (as well as providing track circuit block) for lines that were due for conversion from one to the other. This introduced the ‘plug and play’ connections and lightweight LED signals, which had not previously been used on a standard resignalling, as well as modular components, including CBI data, which did not require site-specific alterations. The lightweight signals, which are of the searchlight type, come in the form of a one-piece base, post and signal head made of a polymer, rather than separate components made from steel, and are hinged to make maintenance easier. Whilst these are primarily manufactured for modular signalling, they are also used extensively for non-modular purposes. So far, only the Shrewsbury to Crewe, Ely to Norwich via Thetford and North Wales Coast lines have been installed in-line with the modular signalling concept.
