Flashing Colour Signal Lights

[sheff'd victoria]

I know in the Sheffield area it is common for the green or double yellow lights on the 4 aspect colour signal to flash , does anyone know which year this started and why they started with this practice

 

[mumrar]

I know in the Sheffield area it is common for the green or double yellow lights on the 4 aspect colour signal to flash , does anyone know which year this started and why they started with this practice

I thought that flashing greens were only on the East Coast mainline, signifying that the next 3 signals are also green. Flashing double or single yellow lets the driver know that a high speed diverging route is set.

 

[O L Leigh]

Ah, this again. Click.

Incidentally, it will be flashing yellows and double yellows, not greens.

O L Leigh

 

[Metroland]

I know in the Sheffield area it is common for the green or double yellow lights on the 4 aspect colour signal to flash , does anyone know which year this started and why they started with this practice

Didcot East, late 1970s. It was because of the introduction of high speed trains and a way to avoid installing 'spitting distants'.

 

[hairyhandedfool]

Flashing yellows were introduced in 1977 on diverging junctions (usually above 50mph), it was later used on 'crossovers' on a single route, however the rule book was not updated to show this at the time.

An accident at Colwich in 1986 saw the rules clarified to say that where there were 'two phase' junctions like Colwich (where signals are present in the middle of the 'junction'), the flashing yellows would only show if the route across the 'entire junction' was clear.

 

[mr_moo]

For the full rule book explanation, go here:
http://www.rgsonline.co.uk/Rule_Boo...8&View={0007ACA4-12EA-4EC3-B2B7-0810CA434F46}
Click on S1, and have a look at section 2.

Note that it's a bit misleading as it shows the signal after the junction as red, which it may not be. If it's green, the junction signal will still show a single yellow until the driver is within sighting distance of it, and it will then change to green in front of the train so the driver knows that he's cleared at full linespeed after the junction. If it's yellow, the junction signal will clear up to a double yellow as the driver approaches.

HTH!

 

[SWT Driver]

Just a point.

There were for a time some flashing greens on the ECML, during trials for high speed running or what is now known as EPS (140mph), these gave the driver an "extra" section or "5th aspect", so a flashing green meant that the next two sections were clear and the train could be driven at EPS speeds, if the signal was a steady green then the driver would have to drop from EPS speed to the standard line speed (125mph).

This was on a section between Helpston & Stoke Bank.

 

[Signalfixer123]

They are still there!
New England North to Stoke Jcn.

 

[O L Leigh]

Does a flashing green have any meaning now? I'm guessing that it doesn't, except perhaps as a 5th aspect indicating only the minimum number of vacant signal sections before the next red.

O L Leigh

 

[Old Timer]

The flashing green aspect controls have been disabled in the Interlocking, although the wiring and control circuits, relays, etc are still there.

There is no reference to them in the Rule Book, and it is unlikely that they will be brought back into use because the current Regulations specify that lineside signals cannot be relied upon at speeds above 125 mph, and thus above that speed, ATC should be provided.

That is why a similar facility was not included in the WCRM upgrade works. The latest thinking is that because any future HS lines will be specially constructed, in-cab ATC will be the standard system, with no lineside signalling.

 

[jon0844]

I have been on a GNER service that hit 140mph (presumably without permission and suggesting the Mk4 had no limiter in operation) some years ago, and it's a real shame that we couldn't have had the line upgraded wherever possible to allow faster running on a pretty straight section of track.

I guess there is a limit on paths and other stock going slower - but if only for recovery purposes, 125-140mph running would certainly help.

(Mind you, it would somewhat destroy the whole fuss over HS1!)

 

[hairyhandedfool]

I'm pretty sure BR wanted faster speeds along the ECML, remember that the 225s were designed with tilt in mind, including space on the loco and stock for the equipment to be fitted at a later date, something that is no longer possible.

 

[Signalfixer123]

They are still there!
They are still flashing merrily away!
New England North to Stoke Junction.

 

[Old Timer]

I have been on a GNER service that hit 140mph (presumably without permission and suggesting the Mk4 had no limiter in operation) some years ago, and it's a real shame that we couldn't have had the line upgraded wherever possible to allow faster running on a pretty straight section of track.

I guess there is a limit on paths and other stock going slower - but if only for recovery purposes, 125-140mph running would certainly help.

(Mind you, it would somewhat destroy the whole fuss over HS1!)

When BR did the calculations some years back, the extra costs of 140 mph running were greater than would be recovered from the anticipated additional traffic generated.

In addition there was the issue of single manning, which could not happen above 125 mph.

In terms of the OHL Equipment, this was made suitable for 125 mph running following some retensioning work, however the equipment is not ideal which is why there are plans to upgrade this section at some point. This also explains the issue with the number of dewirements.

 

[Kneedown]

They are still there!
They are still flashing merrily away!
New England North to Stoke Junction.

I can vouch for that. If we get a new route learner in the cab on a Norich run you can guarantee what the first question will be!

 

[Surreytraveller]

Note that it's a bit misleading as it shows the signal after the junction as red, which it may not be. If it's green, the junction signal will still show a single yellow until the driver is within sighting distance of it,

It's not misleading at all. If a train is approaching a single yellow, the driver MUST expect to stop at the next signal. It is dangerous to assume that the signal beyond is displaying a proceed aspect, as the driver may not be slowing the train enough to stop at the next signal if the single yellow does not change to a less restrictive aspect.

Drivers should be taught there's no such thing as an approach controlled signal.

 

[furryfeet]

is it the case that
a) the junction signal is held at single-yellow until the approach control timing is satisfied that the train has slowed down to the correct speed for the junction ?

b) Only when the correct speed has been reached will the junction signal clear to the highest proceed aspect allowed, according to the NEXT signal on the divergent route after the junction.

 

[Old Timer]

The signalling arrangements at the introduction of Flashing Aspects, required that the Driver must always acknowledge an AWS warning before the jct signal could clear to a green aspect.

In the case of flashing signals, the steady Yellow was held until the train had received the AWS warning at the previous flashing Yellow, after which the signal ahead was then clear to display its highest aspect.

So in simple terms G to Flashing YY to Flashing Y with steady Y in the distance.

After passing the AWS magnet the steady Y could clear to YY or G.

This was done to prevent the driver reading through the flashing aspect and accelerating towards the G and in doing so exceeding the speed for the Jct.

Similar type arrangements can be seen at high speed jcts on multiple track where a train is routed to an adjoing line, the signal ahead of the jct of the line on which the train is travelling FROM is held at RED, whereas the signal next ahead on the line to which the train is travelling towards may show YY or G

 

[NXEA!]

i've seen flashin yellows myself at didcot. it was used to inform the driver that he was crossing over to the slow lines because of engineering work. so whether this happens at sheffield or not i dont know. hope this helps tho.

 

[furryfeet]

At Tamworth, when a train is routed from the up slow to the up fast via a flashing yellow, there are TWO signals at red on the up fast - one in Tamworth station and the other protecting the junction itself, at Amington.

Is this a new standard of having two red signals to prevent a driver on the fast lines overrunning, or has this always been the case in a "flashing yellow" installation ?

 

[Old Timer]

It is the latest method of controlling spads at high risk signals.

 

[royaloak]

Its probably because the red nearest the junction is too close and so has insufficient overlap, so the signalling will double block (2 reds)
Oh you beat me again!

 

[Old Timer]

Sorry Old Chap.

Next time ?

 

[The Planner]

Does a good job of knackering capacity aswell believe it or not.

 

[TDK]

The signalling arrangements at the introduction of Flashing Aspects, required that the Driver must always acknowledge an AWS warning before the jct signal could clear to a green aspect.

In the case of flashing signals, the steady Yellow was held until the train had received the AWS warning at the previous flashing Yellow, after which the signal ahead was then clear to display its highest aspect.

So in simple terms G to Flashing YY to Flashing Y with steady Y in the distance.

After passing the AWS magnet the steady Y could clear to YY or G.

This was done to prevent the driver reading through the flashing aspect and accelerating towards the G and in doing so exceeding the speed for the Jct.

Similar type arrangements can be seen at high speed jcts on multiple track where a train is routed to an adjoing line, the signal ahead of the jct of the line on which the train is travelling FROM is held at RED, whereas the signal next ahead on the line to which the train is travelling towards may show YY or G

There are many locations where the junction signal is not held at a restrictive aspect but will pull off to green way befre the train reaches the signals AWS magnet
--- old post above --- --- new post below ---

It's not misleading at all. If a train is approaching a single yellow, the driver MUST expect to stop at the next signal. It is dangerous to assume that the signal beyond is displaying a proceed aspect, as the driver may not be slowing the train enough to stop at the next signal if the single yellow does not change to a less restrictive aspect.

Drivers should be taught there's no such thing as an approach controlled signal.

They may get taught that but all drivers know what signals are approach control if they have good route knowledge
--- old post above --- --- new post below ---

is it the case that
a) the junction signal is held at single-yellow until the approach control timing is satisfied that the train has slowed down to the correct speed for the junction ?

b) Only when the correct speed has been reached will the junction signal clear to the highest proceed aspect allowed, according to the NEXT signal on the divergent route after the junction.

There are 2 methods of approach control on the routes I drive,one is operated by track circuits, no matter what speed a driver is doing the signal will clear once the approaching track circuit is occupied, the other is with treadles, the same method applies but this method is on a timer but the signal will once again pull off no matter what speed the train is doing

 

[Old Timer]

There are many locations where the junction signal is not held at a restrictive aspect but will pull off to green way befre the train reaches the signals AWS magnet

Principally routes signalled before about 1978/79.

West Hampstead was the first PSB to ge so interlocked.

Previous arrangements included the use of a thermal relay which was heated by the current passing through when energised. At a certain point the relay broke contact and released the junction signal.

The strip was designed to heat up in about two minutes after the occupation of the track circuit beyond the overlap of the signal in rear.

When you had a seriis of trains running through a junction one behind the other the strip got so warm, that aspect release sometimes came shortly after the train passed the signal in rear and not as it was approaching the junction signal. Learnt this through a suspected WSF in the early hours of one morning on one shift.

 

[Surreytraveller]

Note that it's a bit misleading as it shows the signal after the junction as red, which it may not be. If it's green, the junction signal will still show a single yellow until the driver is within sighting distance of it, and it will then change to green in front of the train so the driver knows that he's cleared at full linespeed after the junction. If it's yellow, the junction signal will clear up to a double yellow as the driver approaches.

HTH!

I think you are wrong. It is not that the junction signal is held at yellow - it is the signal beyond the junction which is held at red. The signal beyond the junction is the one that is approach-released, so if a signal at a junction is single yellow, it IS because the next one is red.

 

[The Planner]

Its not, if you come into Brum Int platform 1 or 2, for example the signal prior to the diverge is on a yellow (flashers preceed it), the one on the end of the platform will be green if a route is set.

 

[O L Leigh]

I think you are wrong. It is not that the junction signal is held at yellow - it is the signal beyond the junction which is held at red. The signal beyond the junction is the one that is approach-released, so if a signal at a junction is single yellow, it IS because the next one is red.

Yes and no.

If you get to the junction signal and find that it is still Y it is indeed because the first signal on the diverging route is R. However, it is not because this first signal on the diverging route is approach controlled but because there is some reason why the signal cannot be cleared, such as another train occupying the next signal section. That said, there is no reason why the junction signal at a flashing junction cannot display Y even if the next signal is G.

My own experience of flashing junctions is that the junction signal has always cleared to a less restrictive aspect than Y unless the next signal is being held at R (e.g. the service is being "looped" into a back platform to permit a faster train to pass). However, all junctions of this type on our routes are approached on a curve and the junction signal only comes into view at around the point you're passing over the AWS magnet, so I'm not entirely sure precisely what happens and when. What I have been able to deduce from our most commonly used flashing junction is that if the junction signal can clear to G (even when you know there is absolutely nothing in front of you for miles ahead), it doesn't do so until 300-400 yards away.

O L Leigh