Flashing amber

[AJP]

Ive seen this numerous time whilst on a train. A double yellow flashing. What does this mean??

 

[Craig]

It means the next signal will be set for the highest speed diverging route.

 

[Tomnick]

It's 'advance warning' that the train is signalled onto a diverging route at a junction ahead, as an alternative to 'approach control' (bringing the train nearly to a stand at the protecting signal) where this would be too restrictive. The driver will see the following signals:

• Flashing double yellow (in four-aspect areas)
• Flashing single yellow
• Yellow with appropriate feather (which may further clear to double yellow or green as the train is closely approaching)

 

[tramboy]

That clears up what had been bothering me about the T+W Metro then, as one of the most common places to see this is from the front of a Tyne and Wear metrocar when you are approaching Pelaw Metro Junction (where Metro goes back to South Gosforth control and not Newcastle IECC).

Cheers

Dave

 

[Tomnick]

That clears up what had been bothering me about the T+W Metro then, as one of the most common places to see this is from the front of a Tyne and Wear metrocar when you are approaching Pelaw Metro Junction (where Metro goes back to South Gosforth control and not Newcastle IECC).

Indeed...presumably this is a relatively high speed divergance, and this, combined with the frequency of Metro services, means that 'standard' approach control would cause too many delays.

 

[Max]

That clears up what had been bothering me about the T+W Metro then, as one of the most common places to see this is from the front of a Tyne and Wear metrocar when you are approaching Pelaw Metro Junction (where Metro goes back to South Gosforth control and not Newcastle IECC)

I noticed that when up at newcastle last week. I wondered what on earth it meant until we came to the junction. There's a case of this in KX Simsig north of Welwyn North too I believe.

 

[yorkie]

The best article that describes controlling the speed of approaching trains at junction signals is on Clive Feather's site.

Flashing yellows can be seen in several SimSig simulations. In King's Cross for example: at both sides of Welwyn viaduct, and at Hitchin (the down line is correct, but I am fairly sure the up line will be flashing yellows too as the crossover is 70mph, SimSig incorrectly has this as a 40mph crossover).

It is much better for trains to use flashing yellow junctions as they only have to slow down for the junction and take it at full line speed. Where approach from red is used trains often have to slow down a considerable distance before the junction.

 

[O L Leigh]

It means the next signal will be set for the highest speed diverging route.

Sorry to drag this up from the depths, but the Rule Book has this different. It says:

A flashing yellow aspect means that the facing points at a junction ahead are set for a diverging route, over which the speed of the train must be reduced.

one TN[/quote]

 

[Tomnick]

Think you're both right on this one . The speed of the diverging route in question will be lower than the speed for the 'straight' route - but it will always apply to the highest speed diverging route, with the other (lower speed) diverging routes being signalled more 'conventionally' by approach control etc.

 

[960012]

You get them at woking when u get signalled down the pompey line

 

[Mojo]

Also at Cheddington, for Linslade Junction (not a real junction, but seen where trains on the fasts cross to the slows).

 

[Techniquest]

You get them near Westerleigh Junction (the one where VXC leaves the FGW route after BP) too, as it's a 20mph turnout.

 

[Tomnick]

Not disputing that there's flashing yellows at Westerleigh (Simsig shows them too ), but are you sure that the PSR over the diverging route is as low as 20mph? If that was the case, I'd have thought that approach control from red would have been preferred! I know there's quite a few exceptions, but flashing yellow junction signalling was originally intended for locations where approach control from red would be too restrictive, for example a 50-60mph turnout on a 90mph line.

 

[Mojo]

I know it is very low, and although I don't pay much attention, I did see a 30mph sign to the south of Yate station. Whilst that may be part of a gradual slowdown for the junction, or the actual speed the junction should be taken at, I don't know.

 

[Tomnick]

Ahh, ok. Another one of those exceptions then .

 

[Techniquest]

I'll go hunting and photting the evidence next time I'm on a Voyager down that way then...I'll certainly have to phot the turnout PSR board at Westerleigh Junction on my way to London next time I get a HST!

It WAS 20mph at one point, but that might have been a TSR after they relaid some major amount of track last summer at Westerleigh Junction.

 

[Tomnick]

Give me a flashing green any day .

 

[Techniquest]

Bah, give me half-hourly and better HSTs instead, with right royal Thrashmaster 43s and drivers to go with! HELLFIRE!

 

[Sprog]

I know it is very low, and although I don't pay much attention, I did see a 30mph sign to the south of Yate station. Whilst that may be part of a gradual slowdown for the junction, or the actual speed the junction should be taken at, I don't know.

Westerleigh Junction is 30mph UP and DOWN on the Birmingham line due to the sharp turn off of the Junction. However currently there is a 20mph TSR.

 

[Techniquest]

Still 20mph? Been that for a long time then...Unless it went back to 30 and back down to 20. And yes, it is sharp.

 

[Sprog]

Not disputing that there's flashing yellows at Westerleigh (Simsig shows them too ), but are you sure that the PSR over the diverging route is as low as 20mph? If that was the case, I'd have thought that approach control from red would have been preferred! I know there's quite a few exceptions, but flashing yellow junction signalling was originally intended for locations where approach control from red would be too restrictive, for example a 50-60mph turnout on a 90mph line.

It is not approach controlled id assume, because if it was it would cause too much delay as the Bristol PW - Westerleigh section is quite heavily used by the London Trains, North-bound trains, Locals and not forgetting Freight traffic from Avonmouth, Wales, Bristol and the south-west.

 

[GeoffM]

The current standards for flashing yellows is supposed to be 2/3 line speed, but Westerleigh and Swindon were before those standards IIRC. Swindon varies from the standard in that there are TWO routes from the same signal with flashing yellows - not allowed any more.

Geoff M.

 

[devon_metro]

Is this always the case, looking on Exeter Simsig, there is no flashing amber from DML > Down Torbay where the line speed drops from 60>40, which is 2/3 although it appears to use conventional approach control! Unless this is a fault with Simsig?

 

[ikar]

Is this always the case, looking on Exeter Simsig, there is no flashing amber from DML > Down Torbay where the line speed drops from 60>40, which is 2/3 although it appears to use conventional approach control! Unless this is a fault with Simsig?

The choice (Flashing-Approach control) depends on various things...

 

[devon_metro]

I beleive it is as i remeber witnessing it, unless there was a signal fault!

 

[O L Leigh]

It is much better for trains to use flashing yellow junctions as they only have to slow down for the junction and take it at full line speed. Where approach from red is used trains often have to slow down a considerable distance before the junction.

Sorry, but as others have dragged this one up I feel I must correct something.

The Rule Book now has it that "a flashing yellow aspect means that the facing points at a junction ahead are set for a diverging route, over which the speed of the train must be reduced." However, it does not mean that the junction can necessarily be taken at full line speed, as the normal sequence of signal aspects is flashing double yellow, flashing single yellow, steady single yellow at the junction signal and a red at the first signal on the diverging route.

Although you will often find that the junction signal will be cleared to a less restrictive aspect, you can never rely on this. As a driver, you can never know for sure how fast you can take the junction until you reach the junction signal itself, as you will have no prior warning of it's aspect. Therefore, you have to assume that the first signal on the diverging route is at red and adjust your speed accordingly so that you can stop at it if need be until such time that you can see that this is not the case.

The only advantage that flashing yellow signals convey compared to approach control signalling is that a train can get right across the junction and out of the way sooner than would be the case if they had to stop because the junction signal was at red.

one TN

 

[GeoffM]

and a red at the first signal on the diverging route.

Sorry, but that's incorrect. The first signal on the diverging route is not held at red - the junction signal might *imply* a red but it doesn't mean there *is* a red. Of course, local conditions might require it to be red at the time (another train in front, a controlled signal with no route set, etc), but this is not usually the case.

It should also be noted that the junction signal can clear to a less restrictive aspect (conditions permitting) once the train is within sighting distance of it, normally 200yds - an extra track circuit joint is placed just beyond the AWS ramp for this purpose usually.

As for Exeter SimSig, Mike Miles wrote that one so I can't comment. But he is normally pretty thorough with such things.

Geoff M.

 

[O L Leigh]

Hi Geoff,

I don't believe that I said that the first signal on the diverging route will be held at red. I simply outlined the normal signal sequence at a junction equipped with 4 aspect flashing yellow signals as it is set out in the Rule Book.

As I mentioned, that a junction signal may or may not clear to a less restrictive aspect than a single yellow (denoting that the first signal on the diverging route is at red) cannot be relied upon no matter how often it may do so under normal operating conditions. Assuming that a signal will clear on approach "because it always does" has been the cause of a number of SPAD's over the years. Therefore, as I said before, we always assume that the junction signal will be a single yellow and that the first signal on the diverging route will be a red and drive accordingly until we know for sure that it has cleared to a less restrictive aspect.

Incidentally, the junction signal does not clear within sighting distance, but will clear normally depending on what type of signal it is.

one TN

 

[ikar]

Why are flashing yellows used instead of feathers?

They aren't.

 

[nutter]

Why are flashing yellows used instead of feathers?

Feathers are normally used when it is approach control, ie, the train must treat the signal as a permanant danger (not going to clear in time) until it clears when the train occupies a track circuit closer to the signal, normally between the AWS magnet and the signal head, where as flashing cautions are used to keep the speed up until after the junction, meaning you can get more trains over the junction in the same space of time

As for one TN, what he's saying is = Train divers treat the non-flashing caution before the junction as a normal caution, using flashing cautions as a 'tip' that the signal after the junction is still at danger, even though when they approach the caution it MAY clear to a prilimary or clear, after which, you can carry on at the line speed, although you can not gurantee it clearing, even to a prilimary caution

As with most things on the railways, it's a case of work to the worst case scenario, which is that the caution will not clear, and so the following signal will still be set at danger, so you have to brake as if it is still at danger until the caution clears

Known me, i've just confused even more of you

PS. sorry for been picky about my terminolagy, i got yelled at at HMS sultan for calling them ambers, just a strict instructor i suppose, but a least this way everyone is happy :roll:

Key
Clear = Green = go at full line speed

Flashing Prilimary caution = prepare to stop in 3 signals time, whilst ensuring you meet turnout speed

PC = Prilimary Caution = double Yellow (or single flashing caution)= amber = slow down ready to stop in 2 signals time

Caution = Yellow = amber = prepare to stop at next signal

Danger = stop

I'm getting more like old timer

This post will either clear things up, or totally confuse you