User:Techie3/sandbox/NSW Signalling

Railway signals in New South Wales broadly follow British route signaling 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 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, Bundanoon 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, 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, with the commissioning of (Sydney) Station Box. This installation was electro-pneumatic and controlled from a miniature lever frame supplied by the 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. Upon its replacement by a 432 lever pistol grip power frame in the new Sydney Station West signal box in the late 1920s, the original miniature lever frame was divided into smaller sections for reuse at other locations. The disused 'Station Box' remained in position for decades after its retirement, but has now been demolished, along with its successor.

Track Circuit Block

On 22 June 1913, the first automatic signals in Australia were brought into use between Eveleigh Loco Junction (Illawarra 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 (TCB) worked from mechanical and power signalboxes, with the gradual spread of automatic signalling between stations, became the standard for new installations, initially with semaphore but later colour light signals.

In practice, the term Track Circuit Block was generally shortened to 'Track Block', of which there were a number of (mainly administrative) variations in the rules, such as Double Line Track Block and Single Line Track Block. 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 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.

Signalboxes in 2012

Signalboxes remain scattered throughout the Sydney Trains network, with thirty-six still in regular use in 2012, including nine controlled by local station staff, twenty-six by dedicated Signallers and one shared by both. The majority of these were commissioned before 1970, a few of which have been in continuous use since the late nineteenth century, albeit surviving 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 Signalbox, commissioned in 1936 by W.F. Barton, has the last Westinghouse miniature lever power frame in Australia, and one of few remaining in the world.

Sixteen signalboxes are fitted with route control relay/solid state interlocking systems and hardwired panels, and three are equipped solely with computerised, VDU-based route control. A few other signalling installations exist outside the RailCorp network, under the control of other rail operators. Junee and Broadmeadow are home to integrated electronic control centres, both of which are run by the Australian Rail Track Corporation, custodian of the busiest lines in the country network of the state.

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

The distant signal in NSW has a fixed upper green light

Lower Quadrant Semaphore signals use an arm that works in a horizontal position and may be lowered to 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

UQ semaphore signals, 3 position auto (right) and 2 position distant (left)

The power-operated three-position upper quadrant semaphore signal, American in origin, was introduced to New South Wales by the English signal engineer, C.B. Byles, in 1913. 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, 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

Example	Aspect	Indication	Meaning	Use	Speed Restriction
	Green / Green	Clear	Proceed, expect the next signal to be at a proceed aspect		-
	Green / Blinking Yellow	Preliminary Medium	Proceed, expect the next signal to be Medium	Not always provided	-
	Green / Yellow	Medium	Proceed, expecting next signal to be either Caution, or a turnout indication.	Not always provided, but extremely common	-
	Green / Red	Caution	Proceed, expecting next signal to be at Stop.		-
	Red / Red	Stop	Stop, do not proceed		0
	Red / Red / Yellow	Shunt	Continue to next signal on sight, at no faster than 15 km/h until past the next signal. Be prepared to stop at obstruction or end of Dead End Siding.		15 km/h
	Red / Red / Flashing Yellow	Shunt Ahead	Continue past signal for the purpose of shunting, but do not continue further into the block than necessary for shunting movement.	Extremely Rare	15 km/h
	Red / Red / Small Green	Low Speed	Continue past signal at no greater than 25 km/h, expecting the next signal to be at Stop.	Only used in reduced overlap conditions
	Red / Red / Green (Close Up)	Close Up	(Differentiated from Low speed by having the green aspect in a separate case with "Close Up" written adjacent.) Continue past the signal at no greater than 25 km/h and expect to stop short of train in front.	Used to permit a train to move into the same block as the one in front.	25 km/h (can change)
	Yellow / Yellow	Medium Turnout	Train should pass over junction after signal, once junction/s clear, train can return to line speed. Expect the next signal to be at a proceed aspect.	Used when train is either converging or diverging at junction.	Limited by turnout speed sign.
	Yellow / Red	Caution Turnout	Train should pass over junction after signal, once junction/s clear, train can return to line speed. Expect next signal to be at Stop.	Used when train is either converging or diverging at junction.	Limited by turnout speed sign.
	Red / Red / Offset Yellow	Proceed into Dark Territory	Train will continue through points into a Dead End siding. Light offset in direction of Siding.	Entrance into some Dead End Sidings	15 km/h

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 1924 by C.B. Byles. Most of the Sydney and Newcastle metropolitan areas are equipped with Double Light Colour Light signals, in accordance with principles established during the tenure of Byles, although some of the signals in the outer suburbs has been replaced with Single Light Colour Light. Both systems have almost the same capabilities, with Double Light Colour Light only having a small advantage in aspect variety.

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. 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". Automatic signals in tunnels were originally identified by a white marker light, since the lights could not be staggered, but 'A' plates are now used. More commonly used in the City Circle is a blue 'A' light, which can, when required, extinguish and work as a controlled signal.

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. The Medium indication was introduced in June 1926, three months after the first double yellow indication was used in the UK.

Facing junction signals may exhibit an upper yellow light where a diverging route is set. The yellow light was originally said to mean "attention - proceed at medium speed" in accordance with a 1924 study by the Institute of Railway Signal Engineers in which Byles participated. 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 (originally known as Medium Caution), 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

Original 1932 operation of Sydney's Speed Controlled Trips. Note: The Signal that allows the trains to proceed into the platform is a "Close Up" signal and conflicting sources say that the small lower light was either White, Yellow or Green.

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.

Up until the City Circle Resignalling of the 1990s, the western stations of the line were able to allow a following train into the platform on a Close Up / Low Speed Signal (Red on Red on a small light) and used the trips spread along the platform to ensure that the arriving train would not get too close to the train still departing. This allowed these stations to deal with 42 trains per hour in either direction provided sub 40 second dwell times. The 1990s resignalling changed the older eastern stations to follow a similar operation, only these days the system will not let a following train in until the previous train has departed completely.

In the Underground City and Eastern Suburbs railway lines, 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. Closely spaced 'multi home signals', similar to those used on the London Underground, are also a feature of the Underground City and Eastern Suburbs lines. Speed control by intermediate train stops, based on Byles' system, was introduced on the London Underground following the accident at Moorgate on 28 February 1975, in which 43 people were killed. These are spread out along the platform at major stations, mostly on the City Circle. When the signal at the end of platform is at stop, they will only drop when the train reaches a predetermined speed, which is lower as the train gets closer to the end of the platform. The last trip will only drop when the train is at around 5 km/h.

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 rare cases, the Medium indication will be exhibited at two consecutive signals. At some locations, the Low Speed indication will only be exhibited under reduced overlap conditions (e.g. owing to the presence of a train ahead). Under such a configuration, the sequence of aspects will be: Clear, Medium, Caution, Stop, provided the full overlap is available.

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 equivalent to the British warning ("W") signal for restricted acceptance. Signals fitted with a Close Up lamp case are increasingly rare.

Preliminary medium indications and turnout repeaters

A fifth main aspect, Preliminary Medium, is available, with a pulsating yellow light beneath an upper green. It is often 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. Many automatic signals that are not near junctions can also display the Preliminary Medium indication to give additional warning to freight trains about upcoming red 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(s) 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. The white indicator is proved to be alight before the yellow is displayed.

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

Example	Aspect	Indication	Meaning	Use	Speed Restriction
	Green / Green	Clear	Proceed, expect the next signal to be at Proceed		-
	Green / Blinking Yellow	Preliminary Medium (Advanced Preliminary Caution)	Proceed, expect the next signal to be at Medium (Preliminary Caution)	Not always provided	-
	Green / Yellow	Medium (Preliminary Caution)	Proceed, expect the next signal to be at Caution or a turnout indication.	Not always provided, but extremely common	-
	Green / Red	Caution	Proceed, expect the next signal to be at Stop.		-
	Yellow / Yellow	Medium Turnout	Train shall pass over junction after signal, once the junction/s is cleared, train can return to line speed. Expect the next signal to be at Proceed.	Used when train is either converging or diverging at junction.	Limited by turnout speed sign.
	Yellow / Red	Caution Turnout	Train shall pass over junction after signal, once the junction/s is cleared, train can return to line speed. Expect next signal to be at Stop.	Used when train is either converging or diverging at junction.	Limited by turnout speed sign.
	Red / Red	Stop	Stop, do not proceed		0
	Red / Red / Yellow	Shunt	Continue to next signal on sight, at no faster than 15 km/h until past the next signal. Be prepared to stop at obstruction or end of Dead End Siding.		15 km/h
	Red / Red / Blinking Yellow	Shunt Ahead	Continue past signal for the purpose of shunting, but do not continue further into the block than necessary for shunting movement.	Extremely Rare	15 km/h
	Red / Red / Small Green	Low Speed	Continue past signal at no greater than 25 km/h, expecting the next signal to be at Stop.	Only used in reduced overlap conditions
	Red / Red / Green (Close Up)	Close Up	(Differentiated from Low speed by having the green aspect in a separate case with "Close Up" written adjacent.) Continue past the signal at no greater than 25 km/h and expect to stop short of train in front.	Used to permit a train to move into the same block as the one in front.	25 km/h (can change)
	Red / Red / Offset Yellow	Proceed into Dark Territory	Train will continue through points into a Dead End siding. Light offset in direction of Siding.	Entrance into some Dead End Sidings	15 km/h

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 1924 by C.B. Byles. Most of the Sydney and Newcastle metropolitan areas are equipped with Double Light Colour Light signals, in accordance with principles established during the tenure of Byles, although some of the signals in the outer suburbs has been replaced with Single Light Colour Light. Both systems have almost the same capabilities, with Double Light Colour Light only having a small advantage in aspect variety.

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. 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". Automatic signals in tunnels were originally identified by a white marker light, since the lights could not be staggered, but 'A' plates are now used. More commonly used in the City Circle is a blue 'A' light, which can, when required, extinguish and work as a controlled signal.

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. The Medium indication was introduced in June 1926, three months after the first double yellow indication was used in the UK.

Facing junction signals may exhibit an upper yellow light where a diverging route is set. The yellow light was originally said to mean "attention - proceed at medium speed" in accordance with a 1924 study by the Institute of Railway Signal Engineers in which Byles participated. 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 (originally known as Medium Caution), 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

Original 1932 operation of Sydney's Speed Controlled Trips. Note: The Signal that allows the trains to proceed into the platform is a "Close Up" signal and conflicting sources say that the small lower light was either White, Yellow or Green.

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.

Up until the City Circle Resignalling of the 1990s, the western stations of the line were able to allow a following train into the platform on a Close Up / Low Speed Signal (Red on Red on a small light) and used the trips spread along the platform to ensure that the arriving train would not get too close to the train still departing. This allowed these stations to deal with 42 trains per hour in either direction provided sub 40 second dwell times. The 1990s resignalling changed the older eastern stations to follow a similar operation, only these days the system will not let a following train in until the previous train has departed completely.

In the Underground City and Eastern Suburbs railway lines, 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. Closely spaced 'multi home signals', similar to those used on the London Underground, are also a feature of the Underground City and Eastern Suburbs lines. Speed control by intermediate train stops, based on Byles' system, was introduced on the London Underground following the accident at Moorgate on 28 February 1975, in which 43 people were killed. These are spread out along the platform at major stations, mostly on the City Circle. When the signal at the end of platform is at stop, they will only drop when the train reaches a predetermined speed, which is lower as the train gets closer to the end of the platform. The last trip will only drop when the train is at around 5 km/h.

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 rare cases, the Medium indication will be exhibited at two consecutive signals. At some locations, the Low Speed indication will only be exhibited under reduced overlap conditions (e.g. owing to the presence of a train ahead). Under such a configuration, the sequence of aspects will be: Clear, Medium, Caution, Stop, provided the full overlap is available.

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 equivalent to the British warning ("W") signal for restricted acceptance. Signals fitted with a Close Up lamp case are increasingly rare.

Preliminary medium indications and turnout repeaters

A fifth main aspect, Preliminary Medium, is available, with a pulsating yellow light beneath an upper green. It is often 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. Many automatic signals that are not near junctions can also display the Preliminary Medium indication to give additional warning to freight trains about upcoming red 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(s) 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. The white indicator is proved to be alight before the yellow is displayed.

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

Example	Aspect	Indication	Meaning	Use	Speed Restriction
	Green	Clear	Proceed, expect the next signal to be at Proceed
	Blinking Yellow	Medium (Preliminary Caution)	Proceed, expect the next signal to be at Caution or a turnout indication.	Not always provided	-
	Yellow	Caution	Proceed, expect the next signal to be at Stop		-
	Red / Blinking Diagonal line of Yellow lights	Medium Turnout	Train shall pass over junction after signal, once junction/s clear, train can return to line speed. Expect the next signal to be at Proceed.Yellow lights will be angled in the direction of the turnout.	Used when train is either converging or diverging at junction.	Limited by turnout speed sign.
	Red / Diagonal line of Yellow lights	Caution Turnout	Train shall pass over junction after signal, once junction/s clear, train can return to line speed. Expect next signal to be at Stop. Yellow lights will be angled in the direction of the turnout.	Used when train is either converging or diverging at junction.	Limited by turnout speed sign.
	Red / Red	Stop	Stop, do not proceed		0
	Red / Red / Yellow	Shunt	Continue to next signal on sight, at no faster than 15 km/h until past the next signal. Be prepared to stop at obstruction.		15 km/h
	Red / Red / Blinking Yellow	Shunt Ahead	Continue past signal for the purpose of shunting, but do not continue further into the block than necessary for shunting movement.		15 km/h
	Red / Red / Green (1)	Low Speed	Continue past signal at no greater than 25 km/h, expecting the next signal to be at Stop.	Only used in reduced overlap conditions
	Red / Red / Green (Close Up)	Close Up	(Differentiated from Low speed by having "Close Up" written adjacent to the green aspect.) Continue past the signal at no greater than 25 km/h and expect to stop short of train in front.	Used to permit a train to move into the same block as the one in front.	25 km/h (can change)
	Blinking White	Proceed into Dark Territory	Train will proceed into area controlled by alternative signalling method.	Dark Territory
	Red / Diagonal line of White lights	Diverge into Dark Territory	Train will diverge into area controlled by alternative signalling method, White lights will be angled in direction of diverging route.	Dark Territory	Limited by turnout speed sign.
	Red / Red / Offset Yellow	Shunt into Dead End Siding	Train will continue through points into a Dead End siding. Light offset in direction of Siding.	Dead End sidings	15 km/h

NSW single light signal with band of lights and shunt aspects

With the replacement of older signals in areas with less traffic, Single Light Colour Light signals were introduced in the 1950s by 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.

NSW Dwarf Signals

These signals are in use within SLCL and DLCL Territory.

Example	Aspect	Name	Meaning	Use	Speed Restriction
	2 Red Lights	Stop	Stop, do not proceed	Non-mainline movements	0
	Yellow Light	Caution Proceed	Continue to next signal on sight, at no faster than 15 km/h until you pass the next signal. Be prepared to stop at obstruction.	Non-mainline movements	15 km/h
	Green Light	Proceed	Continue to next signal on sight, at no faster than 15 km/h until you pass the next signal. Be prepared to stop at obstruction. Next Signal is at Proceed, or Caution Proceed.	Non-mainline movements	15 km/h