NSW 5-Aspect Signals

 
  blacktails1985 Station Master

Just wondering if someone could fill me in on why we use 5-Aspect signals for the majority of our network in NSW?

From observing them, they don't seem to offer any new information that a 3-Aspect couldn't, and any new data that could be offered is negated by the fact that the top signal is 2-Aspect, so it can either be Red or Green.

It seems to add an extra layer of complexity to reading the signals.

Unless the top signal is some kind of special shunt signal.

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  seb2351 Chief Commissioner

Location: Sydney
Just wondering if someone could fill me in on why we use 5-Aspect signals for the majority of our network in NSW?

From observing them, they don't seem to offer any new information that a 3-Aspect couldn't, and any new data that could be offered is negated by the fact that the top signal is 2-Aspect, so it can either be Red or Green.

It seems to add an extra layer of complexity to reading the signals.

Unless the top signal is some kind of special shunt signal.
blacktails1985
The system of signalling in NSW differs from the speed signalling used in other states such as SA and VIC in that they do not provide information on what speed to travel. Instead, the signals are used to indicate:
- Authority to enter the block
- The next signal indication.

The top signal, only needs to display green or red because at it's simplest it is the main signal head. It is saying that:
- The block ahead is unoccupied
- The block ahead route is set
- You have permission to enter the block.

With this in mind, it is actually the bottom signal head which is rather redundant, as it is giving you "nice to know" information rather then essential safe-working information. Indeed, if the bottom head is blacked out, but you have a proceed indication on the top head you can still enter the block, but be prepared to find the next signal at stop.

Personally, I prefer the 5 aspect as a driver because it provides me with the necessary information that as I driver I need to ensure that I have my train under control for the situation ahead. A simple 3 aspect signal, while easier on the old grey matter, does not give me enough information about the next signal in advance and as such I need to drive more cautiously in anticpation of events such as:
- Turning out
- Restrictive signals etc

The net effect is that I will be forced to drive my train slower, and if every driver does the same the flow on effects to the network would be extremely disruptive.

Hope this has been of an use to you, at least from the driver's perspective.
  Raichase Captain Rant!

Location: Sydney, NSW
It's also worth pointing out that traditional single light colour light signals can only display stop, caution, medium or proceed (or turnout, or "low speed" or "calling on" etc with the addition of subsidiary lights). A double light colour light signal can also show preliminary medium, which is used when on steep grades, assisting heavier trains in managing their speed when approaching a slow turnout or restricted signals. This is used to good effect when descending from Sutherland to the bridge over Georges River, and when descending from Beecroft towards Epping.
  awsgc24 Minister for Railways

Location: Sydney
It's also worth pointing out that traditional single light colour light signals can only display stop, caution, medium or proceed (or turnout, or "low speed" or "calling on" etc with the addition of subsidiary lights). A double light colour light signal can also show preliminary medium, which is used when on steep grades, assisting heavier trains in managing their speed when approaching a slow turnout or restricted signals. This is used to good effect when descending from Sutherland to the bridge over Georges River, and when descending from Beecroft towards Epping.
Raichase

Another advantage of 5 aspect signalling is that it reduces the ambiguity of repeated mediums.

As discussed in another thread, at North Strathfield, when approaching the junction to the Up North Suburban Flyover, there are two G/Y mediums in a row. This is because the distance between the junction Home signal and the first medium (G/Y) is less that braking distance, and a second medium (G/Y) is required to maintain adequate braking distance.

North Strathfield Flyover junction dates from 1980s, before the Preliminary Mediums (Green over Pulsating Yellow) was defined. Sooner or later G/PY aspects will be provided here.

Ambiguous signals are undesirable because they are ambiguous and have more than one meaning.

Another ambiguity is the Medium aspect (G/Y) which has two meanings:
* Next signal at Caution (G/R) and signal within minimum braking distance is a Stop.
* Next signal at Turnout (Y/R or Y/Y).
** The braking curves and distances may be different for the above two situations.

This ambiguity is being resolved by introducing the "Junction Indicator (JI)", a white diagonal bar above the top Green:
* (G/Y) = next signal at Caution
* (W/ over G/Y) = next signal at Turnout.
* The White Bar is lamp proved before the Bottom Yellow is lit.
** Also, the driver gets more warning if the wrong route is set.
** The oldest JIs at Cabramatta and Merrylands use BR-style 5 white light "feathers".

A good place to see the Junction Indicator is at Birrong since alternate trains generally alternate between the straight and turnout aspects. The new G/Y signal at Concord West approaching the NSFC dive at North Strathfield has a JI.
  KRviator Moderator

Location: Up the front
Just wondering if someone could fill me in on why we use 5-Aspect signals for the majority of our network in NSW?

From observing them, they don't seem to offer any new information that a 3-Aspect couldn't, and any new data that could be offered is negated by the fact that the top signal is 2-Aspect, so it can either be Red or Green.

It seems to add an extra layer of complexity to reading the signals.

Unless the top signal is some kind of special shunt signal.
blacktails1985
As has been said above, for me, the most important is braking distance. IF you have a simple 3 aspect (Stop, Caution or Clear) or 4 aspect (Stop, Caution, Medium, Clear), you might only have 300-400m between signals giving 800-1200m to stop. If you're at track speed and encounter a restrictive indication this can be insufficient unless you go straight for a full service indication, which itself is undesirable for train handling.

More indications means I've got more time to stop the train in a smoother, more controlled manner, in some places using dynamic braking exclusively.
  blacktails1985 Station Master

Maybe it's one of those things that I should just take your word for.
  blacktails1985 Station Master

To seb2351 : I can't see how eliminating the bottom signal could make matters anything but worse. Say we take the stretch of rail from Canley Vale to Merrylands which has 5 aspect signals. If doing as you say and removing the lower signal, all that is left is the upper signal, which is 2 aspect only : It's either red or green. This would be a considerable problem for a driver were the next signal red. This signal can't give a caution, so it gives a green which could mislead the driver into thinking the way is clear, then when he sees the next signal is red.......Westinghouse!!!!!!

Perhaps this part of line isn't such a good example, as in many parts of this and the rest of the south line, the driver can see the next signal. Example, at Canley Vale the next signal is clearly visible.
  gordon_s1942 Chief Commissioner

Location: Central Tablelands of NSW
Many may not know but the '5 Aspect' or multi colour light signals were to be used on the Blue Mountains along with Train Trips to Lithgow and I believe some were actualy installed but never brought into use before being converted to the present Single Head as used today.
One story I heard was that it was changed to the Single Head type because of the cost and the traffic didnt warrant that type of signaling.
For some years a diagram was held in the box at Mt Victoria for the section Katoomba to Mt Victoria showing both Dual heads and trips.
The Bottom marker light started as displaying a permanant white light, the premise was to show the location of the signal if a light in the main head failed.
In later this has now been converted to show a RED when the RED in the head is lit.

How to show a Turnout and what colour to use has caused some headaches over the years and it has been changed several times.

One location was the UP HOME at Katoomba used white lights in the Turnout bar but drivers complained that during daylight, it was hard to see them when the mist rolled in and reduced visibilty as it often did.
  Throughwestmail Train Controller

To seb2351 : I can't see how eliminating the bottom signal could make matters anything but worse. Say we take the stretch of rail from Canley Vale to Merrylands which has 5 aspect signals. If doing as you say and removing the lower signal, all that is left is the upper signal, which is 2 aspect only : It's either red or green. This would be a considerable problem for a driver were the next signal red. This signal can't give a caution, so it gives a green which could mislead the driver into thinking the way is clear, then when he sees the next signal is red.......Westinghouse!!!!!!

Perhaps this part of line isn't such a good example, as in many parts of this and the rest of the south line, the driver can see the next signal. Example, at Canley Vale the next signal is clearly visible.
blacktails1985
I think that is exactly what seb2351 has said, so why argue the point when you agree with him?
  blacktails1985 Station Master

I'm not arguing the point thank you very much. i am seeking more information regarding these types of signals so as to better understand their use and operation and how their various aspects are translated to the driver as opposed to other types of signals.

I think it ignorant to assume I possess this knowledge already and find it offensive that I am just to take what is written at the writers word and not ask questions.

And if you think the question has been successfully answered, why hasn't the thread been closed?
  historian Deputy Commissioner

Part of your confusion might be because you have an incorrect understanding of aspect.

An aspect is what you see; it is the pattern and colour of all the lights showing on the signal. So a typical NSW double light signal with five lights (R/G over R/Y/G) actually only displays four aspects: R/R (Stop), G/R (Caution), G/Y (Medium), and G/G (Clear). Sometimes it may display five aspects with the addition of green over a flashing yellow - G/Y* (Preliminary Medium). But this is a new aspect.

It's a basic principle of signalling that all trains must be able to stop using service braking between the first signal showing a warning aspect and a signal showing stop. The problem is that different trains have vastly different braking capabilities. If lines are signalled according to the worst braking trains (i.e. heavy freight trains with signals a long way apart), this significantly reduces the capacity of the line for the best braking trains (i.e. EMU/DMUs). This is a problem in suburban areas where you want to maximise the capacity for suburban EMUs. Maximising capacity requires signals spaced according to the braking capability of the EMUs. This problem is managed in two ways. The first is to restrict the speed of the worst braking trains to reduce their stopping distance (this is why goods trains have speed restrictions in closely signalled areas). The second is to add more aspects to the basic three aspect system so that a freight train gets an early warning of a Stop signal - this is why you have four and five aspect signalling.

As to why NSW uses double light signals, this is partly historical, partly choice, and partly pragmatic. Historically, NSW first introduced automatic signals before yellow had been adopted for a warning light. NSW adopted the then standard method of indicating three aspects: a home arm over a distant arm (giving aspects R/R, G/R, and G/G). After yellow had been developed for a warning aspect, NSW initially chose not to adopt it, and developed an integrated signal system where all warning signals had two lights (this is why standard mechanical distant signals have a fixed upper green light in NSW). NSW eventually adopted yellow for turnout indications and the medium aspect - the last when capacity became an issue. Single light aspects (where yellow was used as a caution aspect) were eventually adopted for country areas. Initially this was to reduce the power supply requirements.
  gordon_s1942 Chief Commissioner

Location: Central Tablelands of NSW
Regarding 'Historians' comment about Amber or Yellow as a colour for signaling, never when I had an eye test done was that colour used or mentioned, the test was RED, WHITE and GREEN and woe betide you if you even jokingly said 'YELLOW' when one of the WHITE lens appeared 'yellowed' with age.
RED, GREEN, White and 'Purple' were the official 'colours' for all signaling lens dating back to the semaphore days.
Semaphore arms were RED with WHITE stripes on the Front or Face and WHITE with black stripes on the back.
  waxyzebu Locomotive Driver

Just wondering if someone could fill me in on why we use 5-Aspect signals for the majority of our network in NSW?

blacktails1985

As historian indicated, double light colour light signalling as used in the Sydney and Newcastle areas is actually only a four aspect system, which began as a three aspect system replicating the night indications of home and distant semaphore signals. These aspects are directly equivalent to those in other four aspect route signalling systems (e.g. UK, Queensland). The upper yellow turnout indications are a slightly later addition to the system, inspired by speed signalling practice, but are equivalent to the straight route CAUTION or MEDIUM (and therefore not counted as additional aspects for the purpose of your inquiry).

The "fifth" aspects to which you might be referring are not part of the normal aspect sequence or apply to special circumstances.

The PRELIMINARY MEDIUM (green over "pulsating" yellow) indication is inspired by the flashing yellow aspects used in British multiple aspect colourlight signalling and was originally only used on the approach to speed-restricted facing junctions to combat the potential ambiguity of the MEDIUM indication (it was standard practice to exhibit MEDIUM immediately in rear of a junction indication with no other warning of divergence, but MEDIUM may also simply mean that the next signal is at CAUTION. On approach to junctions, MEDIUM is an ambiguous indication with regard to the response required from drivers.). To add confusion, PRELIMINARY MEDIUM now also applies to straight routes at some junction locations, functioning as a "fifth aspect", which has reintroduced ambiguity to the situation (something which testimony from drivers seems to support - the modified junction indications are genuinely aimed at solving certain problems, but the complex array of turnout repeaters and flashing yellows can still be confusing).

LOW SPEED is a reduced overlap CAUTION, to which speed control by timing circuitry and train stops may apply (as in the Underground City Railway, Sydney and Strathfield areas). The speed restriction imposed is 17 mph or less. In some cases, the LOW SPEED indication will only be exhibited where less than the normal overlap is available (Caution being exhibited when the full overlap is available). In the Sydney and Strathfield areas LOW SPEED is sometimes exhibited even if the full overlap is available, effectively functioning as a kind of fifth aspect. A 30 mph speed control also applies to CAUTION in the Underground City Railway and Eastern Suburbs Railway. Where less than the full CAUTION overlap is available, the CAUTION TURNOUT indication may also work in conjunction with speed control (Sydney and Strathfield areas only).

CLOSE UP is the equivalent of a British warning (W) signal, for reduced overlap working at older locations, applying to the "section clear but station or junction blocked" or "warning arrangement" scenario, typically between signal boxes or on accepting/outer home signals. The appearance is similar to LOW SPEED but the subsidiary signal lamp case is labelled CLOSE UP, and speed control does not apply. CLOSE UP has been superseded by approach-controlled CAUTION ("delayed yellow") in resignalling projects. Delayed yellow arrangements also commonly take the place of LOW SPEED, as a reduced overlap CAUTION, outside the Sydney and Strathfield areas.

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