Flashing Green Aspect on Colour Lights

[Ianno87]

I'm sure I noticed a flashing double yellow on the Up Fast north of Stafford a couple of years ago - can anyone remind me of its purpose? (If indeed I did see what I thought I saw)

Turnout into Platform 1 off the Up Fast. Possibly also applies to Platform 4 too.

 

[GC class B1]

Well I believe TASS stands for Tilt And Speed Supervision (above 110mph).
Reportedly, non-tilt stock will soon be running at up to 125mph on the WCML, without TASS.

TASS stands for Tilt Authorisation and Speed Supervision.

 

[hexagon789]

It was a major factor in the Southall collision in 1997.

Indeed and so was the lack of use of the by then fitted ATP system which would have prevented the accident even with the AWS isolation.

America uses speed signalling as opposed to route signalling. The details will differ depending on the railroad but multiple greens would usually

Not exclusively, some route signalling does exist in the States.

I thought that TASS only controls tilt, rather than speed?

It supervises EPS speeds and will implement an intervention brake application if they are exceeded by more than a small margin.

 

[Taunton]

I've never quite understood multiple greens as used in North America (with speeds much lower than 125mph).
What does 4 greens (one above the other) mean? Four clear sections ahead maybe?

I think you can also get a couple of vertical greens in German/Austrian signalling on the rectangular boards they use, seemingly to mimic the old semaphore aspects.
In fact, if I am remembering right, when I first used Paddington (early 60s), the colour lights for the first few miles could give you 2 vertical greens, again maybe mimicking the old semaphore setup of home/distant signals on one post.

I am familiar with US signalling, principles and practice, and although you may get four reds one above the other, I cannot envisage four greens. It's completely different to UK signalling. And if your only USA signal experience is as a tourist on the New York Subway, their signalling is completely different again.

The LMS installed a fully US-standard signalling system as an experiment over about five miles through Mirfield, Yorkshire, in the 1930s, with imported equipment. It lasted to about 1970 when it was replaced with conventional 4-aspect signals. There's one of the original signal masts in the York museum.

Incidentally, as we are speaking about high speed and the lack of cab signals in the UK, in the USA the maximum speed allowed without cab signals is 79mph. This has been a federal requirement since the late 1920s, so surprising the UK has not caught up 100 years later. The cab signals were thus quite widely installed on the later express passenger steam locomotives. At the opposite end of the scale there's still quite a proportion of the US mileage, including many smaller whole railroads, with no signals at all, still done on train orders. Maximum speed allowed there is 59mph.

 

[Ken H]

...
The LMS installed a fully US-standard signalling system as an experiment over about five miles through Mirfield, Yorkshire, in the 1930s, with imported equipment. It lasted to about 1970 when it was replaced with conventional 4-aspect signals. There's one of the original signal masts in the York museum.

..

Wasn't the Watford DC line signalled with something similar?

 

[Taunton]

Wasn't the Watford DC line signalled with something similar?

That was a different principle again (done at the same time), and seemed to be unique, although it shared some characteristics with US subway systems, including the ability to drive just on sight in various situations.

 

[hexagon789]

Incidentally, as we are speaking about high speed and the lack of cab signals in the UK, in the USA the maximum speed allowed without cab signals is 79mph. This has been a federal requirement since the late 1920s, so surprising the UK has not caught up 100 years later. The cab signals were thus quite widely installed on the later express passenger steam locomotives. At the opposite end of the scale there's still quite a proportion of the US mileage, including many smaller whole railroads, with no signals at all, still done on train orders. Maximum speed allowed there is 59mph.

Not 1920s, the ICC order was 1947 after the Naperville crash of 1946 and railroads were given time to comply. The Santa Fe had only until Oct 1952, but others such as the CB&Q were given until the late-1950s.

Also the maximum is not 79mph, the order gives speeds as:

- Cab signals, automatic train stop, or automatic train control wherever passenger trains are operated at speeds of 80 miles per hour or higher

- A block signal system wherever passenger trains operated at speeds of 60 miles per hour or higher

- A block signal system wherever freight trains operated at speeds of 50 miles per hour or higher.

Railroads could set their own limits within these criteria. Simply that 79 happened to be the highest full mph within the block signal requirement but without cab signalling is why 79 became the typical limit.

However, just to emphasise the fact it was by no means set in stone - the Wabash set a 78mph limit for its passenger trains, the Central of Georgia on its dark territory set a 59.9mph limit for its Diesel Streamliner.

79 is simply an arbitrary figure that fits within the less than 80 requirement.

I am familiar with US signalling, principles and practice, and although you may get four reds one above the other

Do you ever get 4? Three reds certainly, which would mean all routes blocked but 4 red signal heads?

 

[najaB]

It supervises EPS speeds and will implement an intervention brake application if they are exceeded by more than a small margin.

Ah right. Minor brain freeze there. What I meant to say was that it doesn't link in to the signalling system so while it can supervise line speed it doesn't work to limit speed based on the signals ahead.

 

[hexagon789]

Ah right. Minor brain freeze there. What I meant to say was that it doesn't link in to the signalling system so while it can supervise line speed it doesn't work to limit speed based on the signals ahead.

Yes, only speed supervision. Unlike ATP which does speed and signals.

TASS is more like an updated C-APT you could say.

 

[The Planner]

Turnout into Platform 1 off the Up Fast. Possibly also applies to Platform 4 too.

Only P1, P4 is approach controlled from red.

 

[sw1ller]

Flashing greens for normal running must be a nightmare. Especially if they’re the new LEDs. There’s a number of locations on my routes I pass flashing yellows and there’s no point in trying to look out the window at the double flash at night. Takes away all your night time vision. I tend to just look away as I get closer. Can’t imagine flashing greens to be any different. That being said though, I find the light intensity of a yellow hurts my eyes more than a green, so maybe it’s not so bad. (I’m still talking about the newer LEDs, I’d be surprised to hear the flashing greens were upgraded to these)

I think I’d consider packing in driving if flashing greens became the norm.

 

[Taunton]

Do you ever get 4? Three reds certainly, which would mean all routes blocked but 4 red signal heads?

Yes, you can have vertically three reds on the upper level for high, medium and slow speed routes, and a lower marker light.

 

[Ken H]

Flashing greens for normal running must be a nightmare. Especially if they’re the new LEDs. There’s a number of locations on my routes I pass flashing yellows and there’s no point in trying to look out the window at the double flash at night. Takes away all your night time vision. I tend to just look away as I get closer. Can’t imagine flashing greens to be any different. That being said though, I find the light intensity of a yellow hurts my eyes more than a green, so maybe it’s not so bad. (I’m still talking about the newer LEDs, I’d be surprised to hear the flashing greens were upgraded to these)

I think I’d consider packing in driving if flashing greens became the norm.

Dont LED signals reduce their light intensity at night in rural locations? Removing night vision is a real issue in many locations. Shining bright lights into the face of a driver at night doesnt sound clever.

 

[centro-323]

Flashing greens are especially fun in heavy fog. You might get an AWS bell and then pass the signal during the unlit phase of the cycle, leading you to wonder what on earth the bell was for!

 

[hexagon789]

Yes, you can have vertically three reds on the upper level for high, medium and slow speed routes, and a lower marker light.

I was thinking more 4 main heads?

 

[alxndr]

(I’m still talking about the newer LEDs, I’d be surprised to hear the flashing greens were upgraded to these)

I'd be more surprised if they hadn't been. The circuitry which controls the flashing is within the location case and not the signal head. Removing the flashing ability would require changing the design, which isn't anywhere near as easy as swapping a filament lamp signal to an LED one.

 

[Ken H]

Flashing greens are especially fun in heavy fog. You might get an AWS bell and then pass the signal during the unlit phase of the cycle, leading you to wonder what on earth the bell was for!

Maritime lights have 3 main light types
Flashing, where the light is off more than on
Isophase. where on and off are equal
Occulting. Where the light is on more than off.

Do these flashing aspects for rail signals have standards and do they roughly align to one of the maritime types. I would think occulting would be safer TBH.

 

[hexagon789]

Maritime lights have 3 main light types
Flashing, where the light is off more than on
Isophase. where on and off are equal
Occulting. Where the light is on more than off.

Do these flashing aspects for rail signals have standards and do they roughly align to one of the maritime types. I would think occulting would be safer TBH.

I believe they are occulting, at least the filament bulb colour lights are.

 

[Tomnick]

Maritime lights have 3 main light types
Flashing, where the light is off more than on
Isophase. where on and off are equal
Occulting. Where the light is on more than off.

Do these flashing aspects for rail signals have standards and do they roughly align to one of the maritime types. I would think occulting would be safer TBH.

They're occulting - approx 70/30 lit/dark if I'm not mistaken.

 

[O L Leigh]

Dont LED signals reduce their light intensity at night in rural locations?

Nope.

 

[martin2345uk]

Nope.

The newer “ultra lightweight” types, that don’t have hoods and look like a swirly flower pattern, are dreadfully bright at night.

 

[O L Leigh]

I'm afraid that I'm going to use this post as a means of lodging a complaint. Sorry if this annoys anyone.

The newer “ultra lightweight” types, that don’t have hoods and look like a swirly flower pattern, are dreadfully bright at night.

They are all unspeakably bright after dark.

It really should not have been beyond the wit of man to have put an auto-dimming feature on them so that they could adjust themselves to whatever the prevailing light conditions are. Many platform lights have this sort of function whereby they brighten when they detect movement nearby. They are so bright that they create dazzle, meaning that anything beyond the signal is, unless it is itself lit, invisible. Many times you have to get ridiculously close to them just to get out of the direct beam and have any chance at all of reading the signal ID plate (which, as a matter of a separate complaint, is now often placed right next to the signal head and therefore almost totally unreadable). My own feeling is that this excessive brightness presents an increased risk of read-through, as it's not always obvious which signals are further into the distance, particularly when they are mounted at different heights.

NS243 (as it may still be known) was recently replaced with LED heads. Now we have one head mounted on the wall directly at eye level with it's matching LED co-actor on the ground in the 6 foot, together with an LED route indicator. Given that you almost always get a double yellow at this signal you have no choice but to shut your eyes or look away otherwise you're blinded. Surely they don't need to be that stupidly bright. The sighting distance is only about 300 yards at the most, and it's in the bottom of a deep cutting between two tunnels so it's not likely to suffer from sunlight interference.

 

[Ken H]

I'm afraid that I'm going to use this post as a means of lodging a complaint. Sorry if this annoys anyone.



They are all unspeakably bright after dark.

It really should not have been beyond the wit of man to have put an auto-dimming feature on them so that they could adjust themselves to whatever the prevailing light conditions are. Many platform lights have this sort of function whereby they brighten when they detect movement nearby. They are so bright that they create dazzle, meaning that anything beyond the signal is, unless it is itself lit, invisible. Many times you have to get ridiculously close to them just to get out of the direct beam and have any chance at all of reading the signal ID plate (which, as a matter of a separate complaint, is now often placed right next to the signal head and therefore almost totally unreadable). My own feeling is that this excessive brightness presents an increased risk of read-through, as it's not always obvious which signals are further into the distance, particularly when they are mounted at different heights.

NS243 (as it may still be known) was recently replaced with LED heads. Now we have one head mounted on the wall directly at eye level with it's matching LED co-actor on the ground in the 6 foot, together with an LED route indicator. Given that you almost always get a double yellow at this signal you have no choice but to shut your eyes or look away otherwise you're blinded. Surely they don't need to be that stupidly bright. The sighting distance is only about 300 yards at the most, and it's in the bottom of a deep cutting between two tunnels so it's not likely to suffer from sunlight interference.

I imagine it's worse in the wet. All the droplets on the unwiped part of the windscreen making tiny lenses. It's the same driving a car. Some traffic lights and reflective road signs are incredibly bright

 

[O L Leigh]

I imagine it's worse in the wet. All the droplets on the unwiped part of the windscreen making tiny lenses. It's the same driving a car. Some traffic lights and reflective road signs are incredibly bright

Never mind the rain, the dead insects or the smear marks left from trying to clear the outside of the windscreen, it's the failure to adequately clean the inside of the screens that makes it worse. It's like they start out with a clean bucket of soapy water that they use to mop down the floors, wipe the tables and clean the loos and then, just before they tip it away, clean the inside of the driver's windscreen. The smearing is so bad that, no matter how clean the outside of the screen is, the whole thing still lights up like Blackpool prom.

Nurse...? Please may I have another one of those nice calming tablets? Thank you.

 

[alxndr]

It really should not have been beyond the wit of man to have put an auto-dimming feature on them so that they could adjust themselves to whatever the prevailing light conditions are.

Not to diminish the problem, because I'll defer to your knowledge that it is a problem when in their beam (I only see them from on foot, which is not within their beam), but I'd be hesitant to just plonk a light sensor on them due to the impact that weather conditions can have.

If it's foggy surely you want them brighter to cut through the fog? A simple sensor can't tell if it's foggy. I don't know if any sensor exists that can tell if it's foggy, other than perhaps some fancy lazer arrangement that would be cost prohibitive to fit at every signal, and fog can be too localised not to. True, we ran a railway before with lights that were not capable of penetrating through fog well, but do we want to go back there?

 

[O L Leigh]

Not to diminish the problem, because I'll defer to your knowledge that it is a problem when in their beam (I only see them from on foot, which is not within their beam), but I'd be hesitant to just plonk a light sensor on them due to the impact that weather conditions can have.

If it's foggy surely you want them brighter to cut through the fog? A simple sensor can't tell if it's foggy. I don't know if any sensor exists that can tell if it's foggy, other than perhaps some fancy lazer arrangement that would be cost prohibitive to fit at every signal, and fog can be too localised not to. True, we ran a railway before with lights that were not capable of penetrating through fog well, but do we want to go back there?

I think we'd cope. You employ a different, more cautious driving technique in fog anyway.

Besides, these LEDs don't tend to cut through the fog. Being brighter just means that they illuminate it and generate even more glare than normal. I think I'd swap the handful of times each year that it's foggy for every time I'm out in the dark getting my retinas cauterised.

 

[edwin_m]

Not to diminish the problem, because I'll defer to your knowledge that it is a problem when in their beam (I only see them from on foot, which is not within their beam), but I'd be hesitant to just plonk a light sensor on them due to the impact that weather conditions can have.

If it's foggy surely you want them brighter to cut through the fog? A simple sensor can't tell if it's foggy. I don't know if any sensor exists that can tell if it's foggy, other than perhaps some fancy lazer arrangement that would be cost prohibitive to fit at every signal, and fog can be too localised not to. True, we ran a railway before with lights that were not capable of penetrating through fog well, but do we want to go back there?

I believe some weather stations can detect fog, I think by shining a laser over a certain distance and measuring the beam at the other end. Obviously not something that could be built into a signal head, but it would perhaps be possible to have these at intervals along the line and somehow communicate to the signal heads to go bright or dim. However the safety case issues would be "interesting", and as the long term plan is to get rid of signals anyway, I doubt anybody is interested in paying for this to be looked at.

 

[seagull]

Yes, approaching some of the LED signals at night is painful for the eyes, quite literally. Two yellows being the worst.
Another issue arising from the over-bright LED heads is that the route indicator, despite being white LEDs, gets "drowned out" and is quite impossible to see at a distance.

 

[alxndr]

I think we'd cope. You employ a different, more cautious driving technique in fog anyway.

Besides, these LEDs don't tend to cut through the fog. Being brighter just means that they illuminate it and generate even more glare than normal. I think I'd swap the handful of times each year that it's foggy for every time I'm out in the dark getting my retinas cauterised.

Fair enough, as I said, I only ever see them from the ground, and to be honest, I tend to avoid going trackside in the fog as much as possible. It can't be a pleasant experience for either of us seeing the other suddenly pop out of the fog, even if I know I'm in a line block.

I believe some weather stations can detect fog, I think by shining a laser over a certain distance and measuring the beam at the other end. Obviously not something that could be built into a signal head, but it would perhaps be possible to have these at intervals along the line and somehow communicate to the signal heads to go bright or dim.

Fog can be very localised. It's not unusual here for it to be a perfectly clear day one side of a dual carriage way and thick fog the other. Thick enough that you would quite legitimately need fog lights on.

 

[sw1ller]

I completely agree with @O L Leigh and @seagull with regards the brightness. There’s a few places I can think of where these signals are placed just in front of a foot crossing and the crossing is completely invisible until you’re about 5-10 yards from the signal and you’re out of the glare.
Yellows seem brighter than red or green too, however, I class yellows as the most important aspect so I’ve no complaints there. And I also agree that route indicators are hard/impossible to read at a distance now with the LEDs.
They 100% need turning down at night and im happy for them to be turned down in fog too.