Australian railway signalling
Encyclopedia
Just as the railways of Australia
has suffered issues from incompatible rail gauge
s, the different states have tended to go their own way regarding railway signalling
practice.
Double Light signals are capable of showing more indications than Single Light signals, therefore Double Light signals are more appropriate for use in dense traffic areas, such as the Sydney
metropolitan area, and Single Light signals for the less intense areas. However combinations of the different types may be found at the same interlocking locations.
and Wingello
on the Main South line in 2007. By 1907, the majority of signalling equipment, including signals and mechanical lever frames, were being manufactured in-house under the direction of the English-born signal engineer, Mr C.L.N.F. Wilkin. The NSWR Signal Engineer's Branch supplanted McKenzie & Holland as the principal supplier in most installations.
'Signal complexes' have been established in various places in the network, where multiple signal boxes are amalgamated into one building. Strathfield Signal Box at Homebush controls from Ashfield to Lidcombe and Epping; Homebush complex from North Sydney to Hornsby and Epping via Chatswood; Sydenham controls the Illawarra and East Hills lines from St Peters to Oatley and Glenfield.
Semaphore distant signals in New South Wales are fitted with a fixed green light, positioned above the arm and spectacle, so that they may be easily distinguished from stop signals at night. Although yellow lights were trialled, neither they, nor yellow and black arms were adopted, meaning that distant signal arms are still painted red and white.
If the Home or Starting signal is at Danger, the Distant signal will be at Caution, its arm in the horizontal position with a green light over a red light exhibited at night. If the Home and Starting signals are Clear, the Distant will be Clear, its arm lowered, with two green lights exhibited at night.
The term "Stop" gradually replaced "Danger" for the purpose of identifying the normal position of stop signals in official publications from circa 1927, with both terms mentioned in the rule book issued in that year.
A basic double light colour light signal consists of two multiple lamp colour light signal heads, one above the other. In case of automatic signals, the upper and lower lights are vertically offset from each other or "staggered". Alternatively, the lower light may be directly below the upper light, like a controlled or semi-automatic signal. An "A" plate is then fixed to the signal post or the tunnel wall adjacent to the signal to identify it as automatic. Interestingly, the term "semi-automatic" is no longer mentioned in official publications, although the signals still exist. They are classified according to their instantaneous mode of operation rather than capability, i.e. "controlled" or "automatic".
The simplest and original form of double light colour light signal provides three indications, that is Clear (green over green), Caution (green over red) and Stop (red over red). A fourth indication, known as Medium, is indicated by green over yellow. This equates to the "double yellow" in British multiple aspect signalling.
Facing junction signals may exhibit an upper yellow light where a diverging route is set. The yellow light was originally said to mean "proceed at medium speed". However, "medium speed" was never properly defined and the term has now been removed from the official rule book. The exhibition of an upper yellow light does not impose a specific speed restriction for approaching trains; it is still the responsibility of the driver to be familiar with the route and observe lineside speed boards relating to points and crossings. The turnout indications are as follows: Caution Turnout (yellow over red), meaning proceed on diverging route, prepared to stop at the next signal, and Medium Turnout (yellow over yellow), meaning proceed on diverging route, the next signal is exhibiting a proceed indication. Oddly, these indications can also be seen at some trailing junctions, at which only one converging route option is available. Whilst the upper yellow light implies that a reduction in speed may be necessary, this is not consistent with conventional route signalling practice. Turnout and junction signals are the most inconsistent and diverse in the NSW signalling system.
The sequence of aspects on the approach to a preceding train in areas where the Low Speed indication is in use is as follows: Clear, Medium, Caution, Low Speed, Stop. In some cases, the Medium indication will be exhibited at two consecutive signals. In addition, the Low Speed indication will not be exhibited unless a preceding train is present at some locations. Under such circumstances, the sequence of aspects will be: Clear, Medium, Caution, Stop.
An additional subsidiary indication below a stop signal is the Close Up. This appears similar to the Low Speed indication, except that the subsidiary green light is provided in a separate lamp case below a plate labelled "CLOSE UP". Speed control does not apply to the Close Up indication, which is manually selected by the Signaller in most cases, and indicates that the section is clear but the station or junction ahead is blocked. Close Up signals are now being superseded by approach-controlled Caution indications for reduced-overlap working.
Directional indicators have been introduced to resolve the ambiguity that may arise when a medium aspect (green over yellow) can precede either a caution aspect (green over red) or one of the turnout aspects (yellow over red/yellow). The indicator is provided at the signal in rear of a junction signal. When illuminated it displays a white bar, inclined at 45 degrees to the left or right, placed above the main signal heads. The bar is not lit when the next signal applies to the straight route, but is illuminated when the next signal applies to the turnout.
At high speed junctions, turnout indications are no longer provided. Instead, the signal in rear of the junction signal is provided with a directional indicator. The junction signal is provided with a route indicator, and exhibits the least-restrictive straight route indication permitted by track circuit occupancy.
Repeaters in the form of Double Light Colour Light signals are provided at some locations in the metropolitan area. These "repeaters" are unusual in that they do not replicate the indication of the stop signals to which they apply. Instead, they are wired like separate block signals or Distant signals. For instance, the repeater will be at green over red when the signal to which it applies is at Stop. The red over red indication will only be exhibited when the line between the repeater and the stop signal is occupied, and is treated as a Permissive Stop.
Originally, a permanently illuminated white marker light was positioned beneath the main colour light head in lieu of the red marker light. The caution turnout indication was a single yellow in the main head over three white lights at an angle of 45 degrees. The red marker light was introduced from 1965. The majority of early single light colour light signals had either been replaced or retrofitted with red marker lights, by 2000.
Some Upper Quadrant Semaphore signals were adapted as Single Light Colour Light signals giving the same colour indications while retaining the arm. The sequence of indications of Single Light Colour Light signals is one green light for Clear, one yellow light for Caution, one red light with a lower smaller red light for Stop. The last Upper Quadrant Semaphore Single Light signal was on the Up South Main Line at Moss Vale, which was replaced in 2007 when Moss Vale and Moss Vale Junction were resignalled, resulting in the closure of local signal boxes at those locations.
On the main south line from Sydney, Single Light Colour Light signals are now exclusively used from Spring Creek bridge (south of Galong) to Albury on the Victorian border. This forms a buffer zone between the areas giving conflicting signal indications. Gradually the remaining Upper Quadrant signals (and Double Light Colour Light signals at Binalong) are being replaced by Single Light Colour Light signals.
The railways of Victoria
use a mix of railway signalling
practices: British route signalling with home and distant signals (2 position signalling) and American speed signalling (3 position signalling).
Semaphore signals
were used on the very first railway lines, but only a bare minimum were provided as the time interval system being relied upon instead. The first interlocking
of signals to protect trains was provided in 1874, as before this time conflicting moves could be made. The design of the signals also progressed, with the disc type siding signals first introduced in 1885, and the lower quadrant somersault type main line signals adopted in 1887, both of which are still in use today. Green was not adopted as the All Right colour until 1898, with white being used before this time. Red was the usually colour of all signal arms, until yellow was chosen as the colour for distant signals in 1926, with full adoption made in 1930. Colour light signals first appeared in 1918, and by 1924 they were the standard for new installations.
The safeworking of trains between stations on the early lines was time interval working, where a train would be allowed to leave a given time after the train before it. With heavier traffic this method became unsafe, with Staff and Ticket working on single lines adopted from 1873, and telegraph block working from 1878 on double lines. Both of these systems ensured that only one train would be in a section of track at one time. Telegraphic block working was then replaced with Winters Block working between 1883 and 1888, a system that is a predecessor of the Double Line Block system which is still used today. Later years saw variations made to the Staff and Ticket system, with busier lines provided with Electric Staff working which provided greater safely when more trains ran.
Heavier suburban traffic on the Melbourne network
saw a greater strain on the block working then used, which required a large number of manned signal boxes to enable trains to run close together. As a result it was decided to adopt power signalling under the Automatic Block System
(ABS) of safeworking, where the presence of trains automatically control the signals after them, providing a safe distance between trains. Introduced from 1915, the system was based on American speed signalling practice with GRS2A upper quadrant mechanical signals with two arms able to indicate up to 5 different speed aspects to train drivers. These signals were later replaced by colour light signals which are the standard today, but the old mechanical style remained until 2001.
A variant of the Automatic Block System, Automatic and Track Control (ATC) has since been introduced, which provides the same benefits as ABS on single lines of track, while still ensuring only one train in a section at a time. Centralised Traffic Control
was also introduced in the 1960s on the new standard gauge line to Albury, and then on the main interstate line to Adelaide, allowing trains to be directed from a distance.
Today little mechanical signalling remains, with local signal box
es controlling signals abolished from many areas as part of the Regional Fast Rail project
. Today the suburban network and busier regional lines use variants of Automatic Block Signalling, while quieter lines use the Train Staff and Ticket
or Train Order systems of safeworking. Train protection has also progressed, with the Train Protection & Warning System also introduced on major passenger lines.
uses two primary forms of signalling. Nearly all signal box
es in South Australia have now been closed, with most rail traffic is coordinated through centralised traffic control
systems, either under Australian Rail Track Corporation
control from Mile End or TransAdelaide
control from Adelaide. Where these two networks interface, such as at the Goodwood level crossing or at Torrens Junction, control is usually from ARTC after release from TransAdelaide. Despite the almost uniform CTC control some signal boxes still exist, such as Dry Creek South although they are not normally switched in.
Hence the aspects are:
In addition to these aspects there was a Yellow over Green aspect for 'reduce to medium speed', used when the next signal showed a medium speed aspect. If either of the two main lights never shows any colour other than red, it is replaced with a permanently lit red marker lamp.
Dwarf signals are also used to show low speed aspects. These were originally upper quadrant disc signals but are now all of the colour light or searchlight variety. The aspects are:
lines were resignalled with the opening of the Adelaide control centre. The system is quite similar to modern UK colour light signalling, being a route signalling system, though it lacks the double yellow aspect and makes use of 'permissive' signals. There are three basic aspects: red for stop, yellow for caution and green for clear. A reduce to medium speed aspect is also used to give early warning of a divergence, and is given by a flashing yellow light. All aspects are indicated with colour light signals. Despite this re-signalling, some parts of the TransAdelaide network still use the original 3-position speed signalling (such as the Dry Creek to Port Adelaide line).
There is also a low speed aspect indicated by a lunar-white position-light signal mounted below the main head. It shows two lunar-white lights at 45 degrees (to mimic an upper-quadrant semaphore) to indicate proceed at low speed. These position light signals are also used for dwarf signals and in this case they can also display 'stop' as a red light and lunar-white light in a horizontal row.
Junctions on running signals are indicated by a row of five lunar-white lights angled in the direction of divergence. If multiple routes are to be signalled, several rows may be used.
Permissive signals are indicated by a circular 'P' plate offset below the signal head and Absolute by a square 'A' plate directly below the signal head. As with three-position signalling, dwarf (low speed) signals are always absolute. An 'A' plate in New South Wales or Victoria means the signal is automatic and therefore a Permissive signal, which is again a source of conflicting meaning between the differing signalling systems.
In the Adelaide station yard Theatre-style route indicators are used on both running signals and shunt signals; platform numbers for 'up' trains and route through the yard for 'down' trains. The down indicators can show these indications:
Rail transport in Australia
Rail transport in Australia is a crucial aspect of the Australian transport network, and an enabler of the wider Australian economy. Rail in Australia is to a large extent state-based. The Australian rail network consists of a total of 41,461 km of track of three major gauges, of which...
has suffered issues from incompatible rail gauge
Rail gauge
Track gauge or rail gauge is the distance between the inner sides of the heads of the two load bearing rails that make up a single railway line. Sixty percent of the world's railways use a standard gauge of . Wider gauges are called broad gauge; smaller gauges, narrow gauge. Break-of-gauge refers...
s, the different states have tended to go their own way regarding railway signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...
practice.
New South Wales
Railway signals in New South Wales broadly follow British route signalling practice, with certain American influences and local innovations. The following systems are currently in use, listed in chronological order of introduction: two-position lower quadrant semaphore, three-position upper quadrant semaphore, Double Light Colour Light and Single Light Colour Light.Double Light signals are capable of showing more indications than Single Light signals, therefore Double Light signals are more appropriate for use in dense traffic areas, such as the Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
metropolitan area, and Single Light signals for the less intense areas. However combinations of the different types may be found at the same interlocking locations.
Systems of train signalling
New South Wales signalling systems generally follow British precepts, however American influence has increased somewhat since the 1990s. Originally trains ran on the time-interval system and authority of the timetable. From the early 1870s, several near-misses and minor derailments led to serious discussion of improved safe-working arrangements and the implementation of interlocking. Despite this, very little action was taken until 1877, when a new rule book including the Staff & Ticket and Block Telegraph systems was finally printed. The ink was barely dry on 30 January 1878 when two trains collided head-on at Emu Plains, killing three. This put an end to timetable working on single lines. Absolute Block Telegraph for double lines came in 1879, Saxby & Farmer's mechanical interlocking in 1881, Tyer's Electric Tablet in 1888 (lasting until 1959) and the Electric Staff system in 1891. Tyer's One-Wire Block began to replace the original Preece's Patent instruments from 1891. Sykes' Lock & Block was used on a few suburban sections from 1900. Tyer's Three-Wire Block was used for permissive block working on the Up Relief line from Concord West to North Strathfield Junction from 1911 until 1983. In 1913, the two-wire New South Wales Standard Block, which was similar in principle to Lock & Block, became the standard for new installations. It was unique in having a fourth position, known as Train Arrived, and a different sequence of operation to standard British arrangements. The last of these instruments were removed from Exeter, BundanoonBundanoon, New South Wales
Bundanoon is a town in the Southern Highlands of New South Wales, Australia, in Wingecarribee Shire. In 2006, Bundanoon had a population of 2,035 people...
and Wingello
Wingello, New South Wales
Wingello is a village in the Southern Highlands of New South Wales, Australia. It is about equidistant between Sydney, the capital of NSW, and Canberra, the nation’s capital. It has a station on CityRail's Southern Highlands line...
on the Main South line in 2007. By 1907, the majority of signalling equipment, including signals and mechanical lever frames, were being manufactured in-house under the direction of the English-born signal engineer, Mr C.L.N.F. Wilkin. The NSWR Signal Engineer's Branch supplanted McKenzie & Holland as the principal supplier in most installations.
Power signalling
Power signalling arrived in 1910 in Sydney Yard. This installation was electro-pneumatic and controlled from a miniature lever frame supplied by McKenzie, Holland & Westinghouse Power Signal Co of Worcester, England. Although the lines were not continuously track-circuited and absolute block telegraph remained between signal boxes, there was some control of signals by track circuit and treadle.Track Circuit Block
On 22 June 1913 the first automatic signals in Australia were brought into use between Eveleigh Loco Junction and Sydenham replacing Tyer's One-Wire Block. These signals were of the two-arm home and distant type. From that time on, a form of Track Circuit Block worked from mechanical and power signal boxes became the standard for new installations, initially with semaphore but later colour light signals. Track Circuit Block, now known officially as the Rail Vehicle Detection system, remains the standard system of train signalling on all main lines in the RailCorp network.Absolute-Permissive Block
The American Absolute-Permissive Block system, known locally as Single Line Automatic, was installed on the Molong to Dubbo line by Mr C.B. Byles in 1925. Train movements on the line were regulated by a Train Controller at Yeoval, who directed the issue of crossing orders for trains on the line. While a technical success, the traffic density did not warrant the cost of maintaining the signalling system. It was replaced by the first installation of the Divisible Miniature Electric Staff system in 1933.Signal boxes in 2009
Signal boxes remain scattered throughout the RailCorp network, with approximately thirty-five still in use in 2009. The majority of these were commissioned before 1970, with a few survivors from the nineteenth century, albeit in a modified state. Eleven are still fitted with Byles-type mechanical lever frames and five have early relay interlocking with Individual Function Switch (IFS) or similar electric switch panels. Newcastle Signal Box, commissioned in 1936 by Mr W.F. Barton, has the last Westinghouse miniature lever power frame in Australia, and one of few remaining in the world.'Signal complexes' have been established in various places in the network, where multiple signal boxes are amalgamated into one building. Strathfield Signal Box at Homebush controls from Ashfield to Lidcombe and Epping; Homebush complex from North Sydney to Hornsby and Epping via Chatswood; Sydenham controls the Illawarra and East Hills lines from St Peters to Oatley and Glenfield.
Three-position lower quadrant semaphore
Standard British three position lower quadrant semaphore signals, with an arm for each direction and spectacles mounted below them, were used from the introduction of time-interval working in 1855. The last signal of this type was removed from Girilambone in 1952. The Danger signal was given by a horizontal arm and red light during darkness. The arm was lowered 45 degrees, with a green light for Caution, to "slacken speed", and to an almost vertical position in a slotted post with a white light for All Right.Two-position lower quadrant semaphore
Lower Quadrant Semaphore signals use an arm that works in a horizontal position and may be lowered to (about) a 45-degree angle, they can only give two indications. In the horizontal position a red light is displayed, in the lowered position a green light is displayed. There are two types of arms. A Distant signal uses a fishtail arm, Home and Starting signals use a square-tail arm.Semaphore distant signals in New South Wales are fitted with a fixed green light, positioned above the arm and spectacle, so that they may be easily distinguished from stop signals at night. Although yellow lights were trialled, neither they, nor yellow and black arms were adopted, meaning that distant signal arms are still painted red and white.
If the Home or Starting signal is at Danger, the Distant signal will be at Caution, its arm in the horizontal position with a green light over a red light exhibited at night. If the Home and Starting signals are Clear, the Distant will be Clear, its arm lowered, with two green lights exhibited at night.
The term "Stop" gradually replaced "Danger" for the purpose of identifying the normal position of stop signals in official publications from circa 1927, with both terms mentioned in the rule book issued in that year.
Combined home and distant signals
Where interlockings are closely placed, a Starting signal arm may be fitted above a Distant signal arm. In this case the Starting arm can be placed at Stop and display a red light. As the lower Distant signal arm cannot be cleared while the upper arm is at Stop the signal will show two red lights. The basis for Double Light signalling was thus established by a sequence of Distant and two-arm signals, so that it was then possible to encounter a signal showing two green lights (Clear), followed by a green light over a red light (Caution) then one or two red lights (Stop).Upper quadrant semaphore signals
The power-operated three-position upper quadrant semaphore signal, American in origin, was introduced to New South Wales by the English signal engineer, Mr C.B. Byles, in 1913. Mr Byles (1871–1948) led New South Wales Railways through its introduction of power signalling, from 1911 until 1929. At night, two lights, one above the other, are exhibited. The spectacle attached to the signal arm has three lenses, that is a green for the vertical clear position and red for the other two lenses. In some cases where an emergency crossover can be cut in for single line working on double track, the semaphore arm moves to the horizontal danger position when the line between the distant signal and the stop signal to which it applies is occupied. The Distant signals capable of exhibiting Danger are fitted with an upper red/green spectacle; the two-position versions have a fixed upper green. The Home/Starting signals give three indications. The arm moves from horizontal displaying a red light, upwards to 45 degrees displaying a green or yellow light, and fully vertical also displaying a green light. In double light areas, the lower light of these signals stays red until a full Clear indication is shown. Therefore these signals will show the same lights indicated by the Lower Quadrant Semaphore Distant and two-arm signals, that is, two greens for Clear, a green over a red for Caution and two reds for Stop.Double light colour light
Double Light Colour Light signalling is essentially a two-light multiple-aspect route signalling system, with aspects derived from the night indications of two-arm Home and Distant semaphore signals. This system was introduced in the 1920s by Mr C.B. Byles. Most of the Sydney and Newcastle metropolitan areas are still equipped with Double Light Colour Light signals, in accordance with principles established during the tenure of Mr Byles.A basic double light colour light signal consists of two multiple lamp colour light signal heads, one above the other. In case of automatic signals, the upper and lower lights are vertically offset from each other or "staggered". Alternatively, the lower light may be directly below the upper light, like a controlled or semi-automatic signal. An "A" plate is then fixed to the signal post or the tunnel wall adjacent to the signal to identify it as automatic. Interestingly, the term "semi-automatic" is no longer mentioned in official publications, although the signals still exist. They are classified according to their instantaneous mode of operation rather than capability, i.e. "controlled" or "automatic".
The simplest and original form of double light colour light signal provides three indications, that is Clear (green over green), Caution (green over red) and Stop (red over red). A fourth indication, known as Medium, is indicated by green over yellow. This equates to the "double yellow" in British multiple aspect signalling.
Facing junction signals may exhibit an upper yellow light where a diverging route is set. The yellow light was originally said to mean "proceed at medium speed". However, "medium speed" was never properly defined and the term has now been removed from the official rule book. The exhibition of an upper yellow light does not impose a specific speed restriction for approaching trains; it is still the responsibility of the driver to be familiar with the route and observe lineside speed boards relating to points and crossings. The turnout indications are as follows: Caution Turnout (yellow over red), meaning proceed on diverging route, prepared to stop at the next signal, and Medium Turnout (yellow over yellow), meaning proceed on diverging route, the next signal is exhibiting a proceed indication. Oddly, these indications can also be seen at some trailing junctions, at which only one converging route option is available. Whilst the upper yellow light implies that a reduction in speed may be necessary, this is not consistent with conventional route signalling practice. Turnout and junction signals are the most inconsistent and diverse in the NSW signalling system.
Reduced-overlap working and speed control
Projected traffic density warranted the introduction of additional signal indications. One of these was a small green light under the two main red lights of a Stop signal, indicating Low Speed. The Low Speed indication was provided in the Underground City Railway from its opening on 28 February 1932. The standard speed restriction imposed by train stops with the Low Speed indication was originally 17 mph. However, at some locations, the maximum permissible speed is as low as 5 mph, subject to local conditions. In the City and Eastern Suburbs Railways, a speed restriction of 30 mph also applies to the Caution indication. The train stops can be seen dropping as the signals step-up to Medium. Speed control by intermediate train stops, based on Mr Byles' system, was introduced on the London Underground following the accident at Moorgate on 28 February 1975, in which 43 people were killed.The sequence of aspects on the approach to a preceding train in areas where the Low Speed indication is in use is as follows: Clear, Medium, Caution, Low Speed, Stop. In some cases, the Medium indication will be exhibited at two consecutive signals. In addition, the Low Speed indication will not be exhibited unless a preceding train is present at some locations. Under such circumstances, the sequence of aspects will be: Clear, Medium, Caution, Stop.
An additional subsidiary indication below a stop signal is the Close Up. This appears similar to the Low Speed indication, except that the subsidiary green light is provided in a separate lamp case below a plate labelled "CLOSE UP". Speed control does not apply to the Close Up indication, which is manually selected by the Signaller in most cases, and indicates that the section is clear but the station or junction ahead is blocked. Close Up signals are now being superseded by approach-controlled Caution indications for reduced-overlap working.
Preliminary medium indications and turnout repeaters
A fifth main aspect, Preliminary Medium, is now available, with a pulsating yellow light beneath an upper green. It is used before a Medium indication to provide additional notice of the need to reduce speed for a facing junction. The typical sequence of aspects on the approach to a junction where Preliminary Medium is in use is as follows: Clear, Preliminary Medium (with or without directional indicator), Medium, Medium Turnout or Caution Turnout at the junction signal. At some locations, Preliminary Medium may be exhibited at two consecutive signals.Directional indicators have been introduced to resolve the ambiguity that may arise when a medium aspect (green over yellow) can precede either a caution aspect (green over red) or one of the turnout aspects (yellow over red/yellow). The indicator is provided at the signal in rear of a junction signal. When illuminated it displays a white bar, inclined at 45 degrees to the left or right, placed above the main signal heads. The bar is not lit when the next signal applies to the straight route, but is illuminated when the next signal applies to the turnout.
At high speed junctions, turnout indications are no longer provided. Instead, the signal in rear of the junction signal is provided with a directional indicator. The junction signal is provided with a route indicator, and exhibits the least-restrictive straight route indication permitted by track circuit occupancy.
Double light colour light repeaters
Repeaters in the form of Double Light Colour Light signals are provided at some locations in the metropolitan area. These "repeaters" are unusual in that they do not replicate the indication of the stop signals to which they apply. Instead, they are wired like separate block signals or Distant signals. For instance, the repeater will be at green over red when the signal to which it applies is at Stop. The red over red indication will only be exhibited when the line between the repeater and the stop signal is occupied, and is treated as a Permissive Stop.
Single light colour light
With the replacement of older signals in areas with less traffic, Single Light Colour Light signals were introduced in the 1950s by Mr D.J. Vernon, Signal Engineer. This system is derived directly from British multiple-aspect signalling, with American influence in the form of a marker light. Using a single green light for Clear and a single yellow light for Caution, these signals exhibit a single red light with a smaller lower red "marker" light for Stop. Turnout indications can be provided with three yellow lights at an angle of 45 degrees under a red light in the main signal head. The fourth indication, Medium, which equates to the British Preliminary Caution, is a flashing or pulsating yellow light.Originally, a permanently illuminated white marker light was positioned beneath the main colour light head in lieu of the red marker light. The caution turnout indication was a single yellow in the main head over three white lights at an angle of 45 degrees. The red marker light was introduced from 1965. The majority of early single light colour light signals had either been replaced or retrofitted with red marker lights, by 2000.
Some Upper Quadrant Semaphore signals were adapted as Single Light Colour Light signals giving the same colour indications while retaining the arm. The sequence of indications of Single Light Colour Light signals is one green light for Clear, one yellow light for Caution, one red light with a lower smaller red light for Stop. The last Upper Quadrant Semaphore Single Light signal was on the Up South Main Line at Moss Vale, which was replaced in 2007 when Moss Vale and Moss Vale Junction were resignalled, resulting in the closure of local signal boxes at those locations.
Contradictory meanings
Signalling systems vary between the states of Australia as each railway was established under the different colonial governments with separate legislation. As with the notorious situation of having different gauges, there are differing signal systems. The Victorian railways use Speed Signalling. This has led to similar signal indications giving very different meanings in these two states. For example, in New South Wales green over red means Caution indicating the next signal is at Stop. In Victoria that same aspect, green over red, means Clear Normal Speed indicating the next signal is anything but at Stop. There is obvious potential for confusion.On the main south line from Sydney, Single Light Colour Light signals are now exclusively used from Spring Creek bridge (south of Galong) to Albury on the Victorian border. This forms a buffer zone between the areas giving conflicting signal indications. Gradually the remaining Upper Quadrant signals (and Double Light Colour Light signals at Binalong) are being replaced by Single Light Colour Light signals.
Victoria
The railways of Victoria
Rail transport in Victoria
Rail transport in Victoria, Australia, is provided by a number of railway operators who operate over the government-owned railway lines. Victorian lines use broad gauge, with the exception of a number of standard gauge freight and interstate lines, a few experimental narrow gauge lines, and...
use a mix of railway signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...
practices: British route signalling with home and distant signals (2 position signalling) and American speed signalling (3 position signalling).
Semaphore signals
Railway semaphore signal
One of the earliest forms of fixed railway signal is the semaphore. These signals display their different indications to train drivers by changing the angle of inclination of a pivoted 'arm'. Semaphore signals were patented in the early 1840s by Joseph James Stevens, and soon became the most...
were used on the very first railway lines, but only a bare minimum were provided as the time interval system being relied upon instead. The first interlocking
Interlocking
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant...
of signals to protect trains was provided in 1874, as before this time conflicting moves could be made. The design of the signals also progressed, with the disc type siding signals first introduced in 1885, and the lower quadrant somersault type main line signals adopted in 1887, both of which are still in use today. Green was not adopted as the All Right colour until 1898, with white being used before this time. Red was the usually colour of all signal arms, until yellow was chosen as the colour for distant signals in 1926, with full adoption made in 1930. Colour light signals first appeared in 1918, and by 1924 they were the standard for new installations.
The safeworking of trains between stations on the early lines was time interval working, where a train would be allowed to leave a given time after the train before it. With heavier traffic this method became unsafe, with Staff and Ticket working on single lines adopted from 1873, and telegraph block working from 1878 on double lines. Both of these systems ensured that only one train would be in a section of track at one time. Telegraphic block working was then replaced with Winters Block working between 1883 and 1888, a system that is a predecessor of the Double Line Block system which is still used today. Later years saw variations made to the Staff and Ticket system, with busier lines provided with Electric Staff working which provided greater safely when more trains ran.
Heavier suburban traffic on the Melbourne network
Railways in Melbourne
The Melbourne rail network is operated by Metro Trains Melbourne under franchise from the Government of Victoria. The network is based on a commuter rail model centred on the Melbourne Central Business District and Flinders Street Station, rather than a rapid transit model, with a focus on...
saw a greater strain on the block working then used, which required a large number of manned signal boxes to enable trains to run close together. As a result it was decided to adopt power signalling under the Automatic Block System
Automatic Block Signal
Automatic Block Signaling, or ABS, is a block system that consists of a series of signals that divide a railway line into a series of blocks and then functions to control the movement of trains between them through automatic signals...
(ABS) of safeworking, where the presence of trains automatically control the signals after them, providing a safe distance between trains. Introduced from 1915, the system was based on American speed signalling practice with GRS2A upper quadrant mechanical signals with two arms able to indicate up to 5 different speed aspects to train drivers. These signals were later replaced by colour light signals which are the standard today, but the old mechanical style remained until 2001.
A variant of the Automatic Block System, Automatic and Track Control (ATC) has since been introduced, which provides the same benefits as ABS on single lines of track, while still ensuring only one train in a section at a time. Centralised Traffic Control
Centralized traffic control
Centralized traffic control is a form of railway signalling that originated in North America and centralizes train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that...
was also introduced in the 1960s on the new standard gauge line to Albury, and then on the main interstate line to Adelaide, allowing trains to be directed from a distance.
Today little mechanical signalling remains, with local signal box
Signal box
On a rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable...
es controlling signals abolished from many areas as part of the Regional Fast Rail project
Regional Fast Rail project
The Regional Fast Rail project was a rail transport project of the State Government of Victoria, Australia undertaken between 2000 and 2006 aimed at improving the passenger services on the Victorian regional railway network , specifically to reduce travel times, enhance service frequency and...
. Today the suburban network and busier regional lines use variants of Automatic Block Signalling, while quieter lines use the Train Staff and Ticket
Token (railway signalling)
In railway signalling, a token is a physical object which a locomotive driver is required to have or see before entering onto a particular section of single track. The token is clearly endorsed with the name of the section it belongs to...
or Train Order systems of safeworking. Train protection has also progressed, with the Train Protection & Warning System also introduced on major passenger lines.
South Australia
South AustraliaRail transport in South Australia
The first railway in colonial South Australia was a horse-drawn tramway from the port of Goolwa on the Murray River to an ocean harbour at Port Elliot in 1854...
uses two primary forms of signalling. Nearly all signal box
Signal box
On a rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable...
es in South Australia have now been closed, with most rail traffic is coordinated through centralised traffic control
Centralized traffic control
Centralized traffic control is a form of railway signalling that originated in North America and centralizes train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that...
systems, either under Australian Rail Track Corporation
Australian Rail Track Corporation
Australian Rail Track Corporation is a federal government owned corporation established in 1997 that owns, leases, maintains and controls the majority of main line standard gauge railway lines on the mainland of Australia, known as the Defined Interstate Rail Network .-History:The Interstate...
control from Mile End or TransAdelaide
TransAdelaide
TransAdelaide was a publicly owned corporation which provided suburban train and tram services in Adelaide, South Australia, under contract to the Government of South Australia....
control from Adelaide. Where these two networks interface, such as at the Goodwood level crossing or at Torrens Junction, control is usually from ARTC after release from TransAdelaide. Despite the almost uniform CTC control some signal boxes still exist, such as Dry Creek South although they are not normally switched in.
Speed signalling
Before 1988, signalling in the metropolitan area was three position speed signalling, similar to the Victorian system. All mainline signals have two signal 'heads' (originally upper quadrant semaphore arms but now colour light, LED or searchlight), both are always lit. The aspects shown depend on the speed of the route set. If the route was for normal speed, the indication is given by the top head, if the move is for medium speed (40 km/h, such as when entering a loop or siding), the indication is given by the lower head. The colours displayed by either depended on how many blocks ahead were clear, green if two or more blocks were clear and yellow if only one was clear (i.e. the next signal showed stop).Hence the aspects are:
- Red over red: Stop.
- Green over red: Normal Clear.
- Yellow over red: Normal Caution.
- Red over green: Medium Clear.
- Red over yellow: Medium Caution.
In addition to these aspects there was a Yellow over Green aspect for 'reduce to medium speed', used when the next signal showed a medium speed aspect. If either of the two main lights never shows any colour other than red, it is replaced with a permanently lit red marker lamp.
Dwarf signals
There is also a low speed aspect for calling-on, shunting or entering a low speed area such as a goods siding. This is indicated by a small yellow light beneath the two main lights, i.e. red over red over yellow.Dwarf signals are also used to show low speed aspects. These were originally upper quadrant disc signals but are now all of the colour light or searchlight variety. The aspects are:
- Single red or purple light: Stop.
- Single yellow light: Low Speed Caution (block may be occupied).
- Single green light: Low Clear (next signal is clear or caution).
Permissive vs absolute
Signals are divided into Permissive and Absolute signals. Absolute signals cannot be passed at stop without permission from the signaller, whereas Permissive signals at stop can be passed after waiting one minute. Absolute signals can be identified by the fact that the two lights are aligned vertically, whereas in Permissive signals they are staggered (on different sides of the post). Dwarf signals are always Absolute.Suburban network
In 1988 the TransAdelaideTransAdelaide
TransAdelaide was a publicly owned corporation which provided suburban train and tram services in Adelaide, South Australia, under contract to the Government of South Australia....
lines were resignalled with the opening of the Adelaide control centre. The system is quite similar to modern UK colour light signalling, being a route signalling system, though it lacks the double yellow aspect and makes use of 'permissive' signals. There are three basic aspects: red for stop, yellow for caution and green for clear. A reduce to medium speed aspect is also used to give early warning of a divergence, and is given by a flashing yellow light. All aspects are indicated with colour light signals. Despite this re-signalling, some parts of the TransAdelaide network still use the original 3-position speed signalling (such as the Dry Creek to Port Adelaide line).
There is also a low speed aspect indicated by a lunar-white position-light signal mounted below the main head. It shows two lunar-white lights at 45 degrees (to mimic an upper-quadrant semaphore) to indicate proceed at low speed. These position light signals are also used for dwarf signals and in this case they can also display 'stop' as a red light and lunar-white light in a horizontal row.
Junctions on running signals are indicated by a row of five lunar-white lights angled in the direction of divergence. If multiple routes are to be signalled, several rows may be used.
Permissive signals are indicated by a circular 'P' plate offset below the signal head and Absolute by a square 'A' plate directly below the signal head. As with three-position signalling, dwarf (low speed) signals are always absolute. An 'A' plate in New South Wales or Victoria means the signal is automatic and therefore a Permissive signal, which is again a source of conflicting meaning between the differing signalling systems.
In the Adelaide station yard Theatre-style route indicators are used on both running signals and shunt signals; platform numbers for 'up' trains and route through the yard for 'down' trains. The down indicators can show these indications:
- SS-south suburban line,
- SM-south main line,
- PM-port main line,
- NM-north main line,
- RD-rail car depot,
- SY-stabling siding,
- NY-north yard.
Queensland
Follows UK practice, except that flashing yellow allows simultaneous entry into a crossing loop with no overlaps.Western Australia
Follows a practice similar to UK modern colour light signalling with junctions being signalled with rows of five lunar-white lights (also known as 'feathers'), though there are still many older colour light junction signals where a signal head of variable height was provided for each route.External links
- http://extranet.artc.com.au Australian Rail Track CorporationAustralian Rail Track CorporationAustralian Rail Track Corporation is a federal government owned corporation established in 1997 that owns, leases, maintains and controls the majority of main line standard gauge railway lines on the mainland of Australia, known as the Defined Interstate Rail Network .-History:The Interstate...
website where NSW signalling standards, principles, safeworking rules are available. - Safeworking systems in Victoria (Australia)