The new LED signals, telling 2 & 3 aspects apart

[brad465]

Something I've always wondered, as more colour light signals on the rail network and semaphores, are replaced with the modern LED signals combining multiple aspect lights into one LED point, the following:

How do drivers tell 2 and 3 aspect signals apart? I would assume they are told this in route training, but sometimes it could be hard to remember everything to such detail.

 

[louis97]

One simple answer, route knowledge - comes with the job.

 

[brad465]

So sort of what I thought originally, only it must annoy enthusiasts in travelling new routes for them

 

[Railsigns]

The SDO signals in the Manchester South area are even more of a challenge: 2, 3 and 4 aspect signals all look the same (they all have two-lens heads).

 

[Rich McLean]

There are also some 2 headed LED 4 aspect signals about

4 Aspect Example
Danger - Bottom Red steady red, upper head blank
Single Yellow - Bottom Steady Yellow, upper head blank
Double Yellow - Both Heads Yellow
Proceed - Bottom head Green, upper head Blank

There are many different variations. In short, one head can provide 3 aspects (red, single yellow, green), sometimes 2 head LED can be used for 3 aspect. It's all down to the route, and highlights how important route knowledge is. Sometimes it can throw a driver off guard if newly installed, and you will get briefed about them as they go live

 

[Harbon 1]

There are also some 2 headed LED 4 aspect signals about

4 Aspect Example
Danger - Bottom Red steady red, upper head blank
Single Yellow - Bottom Steady Yellow, upper head blank
Double Yellow - Both Heads Yellow
Proceed - Bottom head blank, upper head Green

There are many different variations. In short, one head can provide 3 aspects, sometimes 2 head LED will do that same. It's all down to the route, and highlights how important route knowledge is

The 4 aspect heads have to have 2 heads as they need the seperation of the two yellow aspects to be visible. The bottom head shows Red/Yellow/Green and the upper shows only Yellow.

The Dorman 3 aspect heads have a curved area in the top to allow the addition of a second head for upgrading to 4 aspect signalling,

Thought though, when upgrading say semaphore signalled lines to colour light, wouldnt it be done to 3 aspect signals set braking distances apart like conventional multi-aspect signalled lines, eg doing away with the semaphore operation of YG, RG sequences?

 

[carriageline]

And plus, 2 aspect will have an associated repeater not that that helps massively


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[Llanigraham]

So sort of what I thought originally, only it must annoy enthusiasts in travelling new routes for them

But we don't run the railway for the enjoyment of enthusiasts! (Thankfully!!)

 

[TDK]

All route risk assessments will have the transition from 2 to 3 to 4 aspect signalling and there should be a question in the assessment asking the driver to identify where this occurs as evidence that the driver knows the signalling sequencing of the route.

 

[BantamMenace]

Can I ask why it is important for drivers to know how many aspects a signal is as one yellow always means the next is red regardless of whether double yellows are used on that route or not

 

[455driver]

Can I ask why it is important for drivers to know how many aspects a signal is as one yellow always means the next is red regardless of whether double yellows are used on that route or not

Braking distance, the distance from a single yellow to a red will be much further on (high speed) 2 aspect signalling than it will be on 4 aspect signalling.

 

[Beano123]

Braking Distance is the simple answer. All signals are a different distance apart, the driver relies on route knowledge to tell him how far he's got to brake.

Stockport's signals, for example, are a lot closer together than those controlled by Manchester South. Generally on the Crewe line you can pass a single yellow at a far higher speed than signals in the Stockport area.

The braking distance from a 4 aspect signal (previous signal being 3 aspect) at a single yellow to the red can be far shorter than you expect. The Up Bolton after Clifton is a good example - plenty of time if its a double yellow on the approach to Clifton to brake for Salford Crescent. If its a single yellow (first 4 aspect signal) then you need to brake sharpish to get the speed down.

Also important is that if a driver is expecting double yellows at the single he may incorrectly respond to a single yellow. Awareness of the change in aspect number means the driver can up there concentration and guard against such risks.

 

[deltic08]

I just assumed drivers drove to LED aspect showing and not what the head looks like. From a distance the head looks black anyway with only colours showing.

Again I assume there is a minimum space between the two spectacles for distinguishing double yellows from single from the previous signal but if passing a green and the next signal in the distance is yellow or double yellow even if unable to tell, the driver starts braking.

I was at Leyland a few weeks back where signalling has been converted to LED. The signals on both up lines immediately to the south of the station have a flashing single yellow facility because the next set of up signals with feathers to the south control Euxton Junction where there is a 60mph turnout speed onto the Bolton line from the mainline where speed is 125mph.

Even from the platform end I was unable to tell if the flashing single yellow was from the lower red/yellow/green LED or from the higher single yellow spectacle. Assuming once again the previous up signal on the other side of Leyland station was displaying flashing double yellows.

 

[BantamMenace]

So after passing a green at 125mph on the straight you can see a double yellow, followed by a yellow and then a red would you start braking straight away or would you wait until a braking point you know will stop you at the red hence treating the red as if it were a station?
Southbound through Crewe I think you can see the next three signals in line but I'm unsure whether it's 125mph through there.

 

[SpacePhoenix]

A related question, where there's now LED signals, with just the one aspect (the one that can show red, yellow or green), can they easily be converted to "4 aspect" (with the second yellow aspect for preliminary caution) or do the cabinets need a rewire for that to happen?

 

[The Planner]

Thought though, when upgrading say semaphore signalled lines to colour light, wouldnt it be done to 3 aspect signals set braking distances apart like conventional multi-aspect signalled lines, eg doing away with the semaphore operation of YG, RG sequences?

Not always, quite often they are resignalled to 2 aspect colour light with similar distances.

 

[Railsigns]

A related question, where there's now LED signals, with just the one aspect (the one that can show red, yellow or green), can they easily be converted to "4 aspect" (with the second yellow aspect for preliminary caution) or do the cabinets need a rewire for that to happen?

Upgrading a signal (LED or otherwise) from 3-aspect to 4-aspect will always entail work in the location cabinet. It may also require additional circuits between signals to pass the aspect information or (where SSI etc.) an interlocking data change.

 

[HarleyDavidson]

The replacement signal heads around Clapham and Waterloo are just 2 aspect one's, but they're the same size as a 3 aspect one, except that there's no middle aspect.

They're fine albeit a little too bright close up. The signal at Dorking is an all in one (possibly Dorman) one, which has two aspects (4) and "calling on" position light signal & route indicator what appears to be a whole sealed unit.

 

[MarkyT]

There's no difference in the sequences of aspects seen by the driver whether individual signals have 2 or 3 aspects. The only major difference is under failure conditions, as drivers must treat a dark, unillluminated signal as being at it's most restrictive aspect meaning an emergency stop if the signal has a red aspect. Two aspect signalling has distant signals that have no red aspect however, so the required action on encountering a dark one is to brake normally expecting the following signal to be at red. Distant signals without reds are identified by a white triangle symbol above the number on the ID plate.

 

[Tomnick]

Just to add, also, that this isn't a new situation! There are plenty of 'conventional' signal heads in existence with more apertures than necessary to display the required aspects - either provided as 'future-proofing' with the intention of later commissioning extra signals and bringing another aspect into use, blanking off apertures as other signals are taken out of use or, in some cases, simply to allow a signal head from elsewhere to be reused. It's not a new problem, not that it's actually a problem at all.
--- old post above --- --- new post below ---

Thought though, when upgrading say semaphore signalled lines to colour light, wouldnt it be done to 3 aspect signals set braking distances apart like conventional multi-aspect signalled lines, eg doing away with the semaphore operation of YG, RG sequences?

That depends entirely on the capacity that they're hoping to achieve from the scheme. If it's 'like for like', then, as The Planner says, you might find them replaced with 2-aspect signals approximately in the position of the former block posts. Sometimes, mechanical signalling is replaced by colour light signalling whilst retaining Absolute Block working - Appleby and Elsham, in North Lincs, are good examples. There, the 'textbook' layout of distant (Y/G), home (R/Y/G) and starter (R/G) has been retained on the Down at Elsham, but with the latter moved right out to braking distance from the home - thus slightly easing the long section from there to Appleby. There aren't any additional signals though.

 

[HarleyDavidson]

Another oddity is at Portsmouth Harbour, where you have a 4 aspect head, but only 3 aspects available.

You get 2 yellows & platform number you're into the platform. However you can get one yellow & platform number & you're NOT in, you're only cleared to the signal on the end of the platform!

Yes! Some bright spark (read idiot signalling engineer/designer) put signals directly behind the platform starter, so you have about 50m before you come to the next signal, which all being well will release the "calling on" signal to enter an occupied platform.

You'd think though that when they did PARS that they'd use LED signals, but they used standard filament signals instead.

 

[LNW-GW Joint]

So after passing a green at 125mph on the straight you can see a double yellow, followed by a yellow and then a red would you start braking straight away or would you wait until a braking point you know will stop you at the red hence treating the red as if it were a station?
Southbound through Crewe I think you can see the next three signals in line but I'm unsure whether it's 125mph through there.

80mph on the through lines, severe approach control on any other routeing.
It soon relaxes to 110mph but it's a couple of miles in either direction before you get 125EPS.

 

[Tomnick]

Another oddity is at Portsmouth Harbour, where you have a 4 aspect head, but only 3 aspects available.

You get 2 yellows & platform number you're into the platform. However you can get one yellow & platform number & you're NOT in, you're only cleared to the signal on the end of the platform!

Yes! Some bright spark (read idiot signalling engineer/designer) put signals directly behind the platform starter, so you have about 50m before you come to the next signal, which all being well will release the "calling on" signal to enter an occupied platform.

You'd think though that when they did PARS that they'd use LED signals, but they used standard filament signals instead.

Is that to minimise the distance between a calling-on aspect and the occupied platform? There is a maximum distance somewhere in the design standards, presumably to minimise the risk of a driver forgetting that he's coming into an occupied platform. It's quite often done on the approach to busy through platforms too (London Bridge Controls?) to allow a second train to start moving towards the platform (still protected by the signal immediately in rear) whilst the first train is still leaving - obviously that doesn't apply there though.

 

[Deepgreen]

Essentially, the delivery method for the coloured light output is irrelevant here - route knowledge (i.e. line speed, signal spacing, etc.) will dictate driving technique, and LED lights would be treated exactly the same as filament lights. Drivers need not be concerned whether, for example, a green aspect is delivered by LED from the lower of two lenses or by filament from a higher one, as the exact position of each aspect on the signal head is only apparent when very close up. A blank (unlit) signal will be treated the same whether of the LED or filament type.

 

[MarkyT]

Another oddity is at Portsmouth Harbour, where you have a 4 aspect head, but only 3 aspects available.

That's quite common in itself on approach to a terminal in 4 aspect where an outer home wouldn't have a green.

You get 2 yellows & platform number you're into the platform. However you can get one yellow & platform number & you're NOT in, you're only cleared to the signal on the end of the platform!

There are arguments for this arrangement (I'm not saying I agree with them!):

1. A call on move from the extra incoming platform signal can before it gets there travel faster through the throat than if the position light had been given back at the proper home, where the entire route would be limited to 15MPH.

2. The call on move is limited in length so that any obstruction is visible from the authorising signal.

I think the benefits of 1 are negligible and not worth the extra equipment and complexity as long as you can place the home signal as close as possible to the terminal throat. 2 is more difficult because at the time layout plans were being developed there were many concerns circulating about collisions in permissive platforms of which there had been a spate.

Platform run-in end signals like this can be very useful on busy THROUGH platforms, as they can perform a "closing up" function, allowing a following train to approach closer in behind the previous departing train, but I don't think they make much sense at a terminal.

You'd think though that when they did PARS that they'd use LED signals, but they used standard filament signals instead.

The Siemens signalling control equipment at the time was not compatible with LED signals. Even the standard filament units had to be modified to suit.

 

[OuterDistant]

There, the 'textbook' layout of distant (Y/G), home (R/Y/G) and starter (R/G) has been retained on the Down at Elsham, but with the latter moved right out to braking distance from the home [...]

Sorry if this is slightly off topic, but I take it that if this change hadn't taken place and the section ahead was blocked, in the "textbook layout" a driver would see the distant at Y, home at R (which then cleared to Y), and would then draw up to the starter at R?

The reason I ask is that I used to play BVE and on one of the activities, you would see the distant at G and the home at Y, but would barely have applied the brake before you were charging through the station and overrunning the starter at R. Grrr!

I always assumed that the route was incorrectly set up and the home should actually be a 2-aspect signal, but now I'm not so sure!

 

[Tomnick]

If the home signal is a colour light reading straight to the section signal, then it should be a 3-aspect (or 4-aspect, potentially) signal, as otherwise you'd be going from a G to a R, which isn't permitted* according to the principles of signalling. Where BVE has gone wrong, in the case where full braking distance isn't available between the home signal and the section signal, is allowing the former to clear straight to a yellow - it should be approach controlled in that case.

* - except for semaphore signals (but, with very few exceptions, they shouldn't be cleared until the approaching train is quite or nearly at a stand if the next signal is at danger) and part of the Mersey Loop (which relies on drivers sighting the stop signal directly).

 

[HarleyDavidson]

That's quite common in itself on approach to a terminal in 4 aspect where an outer home wouldn't have a green.



There are arguments for this arrangement (I'm not saying I agree with them!):

1. A call on move from the extra incoming platform signal can before it gets there travel faster through the throat than if the position light had been given back at the proper home, where the entire route would be limited to 15MPH.

2. The call on move is limited in length so that any obstruction is visible from the authorising signal.

I think the benefits of 1 are negligible and not worth the extra equipment and complexity as long as you can place the home signal as close as possible to the terminal throat. 2 is more difficult because at the time layout plans were being developed there were many concerns circulating about collisions in permissive platforms of which there had been a spate.

Platform run-in end signals like this can be very useful on busy THROUGH platforms, as they can perform a "closing up" function, allowing a following train to approach closer in behind the previous departing train, but I don't think they make much sense at a terminal.



The Siemens signalling control equipment at the time was not compatible with LED signals. Even the standard filament units had to be modified to suit.

Well I can tell you that the signalling down there is a joke, most drivers who've been on the plate think it's "rubbish"

The sections are too short particularly between Southsea & Harbour, where a 12 car bridge two signal sections so instantly negates any sort of benefit from the resignalling, the number of SPAD traps quadrupled from 4 to 16, the computer thinks it's operating a German points machine and regularly throws a wobbler! Perhaps it's just as well it uses normal filament signals rather than LEDs, because it would probably have a complete computer "nervous breakdown".

TBQH modern day signalling engineers & designers couldn't (CENSORED!).

 

[Railsigns]

TBQH modern day signalling engineers & designers couldn't (CENSORED!).

... care less what people on public forums may think about them.

 

[moggie]

TBQH modern day signalling engineers & designers couldn't (CENSORED!).

Clueless. You need to go and sit down in a quiet room.