Approaching cautionary signals...

[Bigfoot]

From the passenger's perspective it's often intriguing how quickly (or not) a train slows on sighting a double yellow. On my local Snow Hill line for example, with a line speed of 75mph, trains used to approach Kidderminster at a fair pace from the north even on double yellow but often nowadays reduce speed dramatically and trundle into the station. Maybe the timetable is so slack there's no need to wear the brake discs out? Or maybe it's better to just ensure a slow enough speed in case the signal at the end of the platform turns red?

Given the majority of modern stock don't really use much friction braking a lot of the time pad/disc wear theories go out the window. Reho/regen does most of the work with friction taking a back seat until slow speeds/emergency the majority of the time.

 

[Skie]

Thanks. What does it stand for?

Send Green

 

[CW2]

So do you consider a flashing double yellow as a cautionary signal, or do you treat is as a Green-with-extra-information?
How does your TOC / FOC teach you to approach flashing double yellows.
(For the uninitiated, flashing double yellow aspects can be installed on the approach to a (relatively) high-speed turnout, provided the route is clear through the junction, so instead of successive signals being Green, Double Yellow, Single Yellow, Red, which - if the route is clear - then clears to a proceed aspect once a track circuit timer has ensured the train has slowed down, instead you get Flashing Double Yellow, Flashing Single Yellow, (steady) Single Yellow releasing to Green once the track circuit timer is passed. The flashing sequence informs the driver the route is set through the junction to the diverging line).

 

[PudseyBearHST]

So do you consider a flashing double yellow as a cautionary signal, or do you treat is as a Green-with-extra-information?
How does your TOC / FOC teach you to approach flashing double yellows.
(For the uninitiated, flashing double yellow aspects can be installed on the approach to a (relatively) high-speed turnout, provided the route is clear through the junction, so instead of successive signals being Green, Double Yellow, Single Yellow, Red, which - if the route is clear - then clears to a proceed aspect once a track circuit timer has ensured the train has slowed down, instead you get Flashing Double Yellow, Flashing Single Yellow, (steady) Single Yellow releasing to Green once the track circuit timer is passed. The flashing sequence informs the driver the route is set through the junction to the diverging line).

One of the biggest things that companies will stress on drivers in regard to flashing yellows is to approach the junction signal expecting a steady yellow so control the speed of your train accordingly. Don’t expect it to be green even if it is 99% of the time. If there is a signal beyond the junction but before the station, these tend to be high risk/MultiSPAD signals because when drivers see flashing yellows, there is a tendency to assume that you are clear into the station when in fact, there is a red signal just before the station.

 

[MichaelAMW]

So do you consider a flashing double yellow as a cautionary signal, or do you treat is as a Green-with-extra-information?
How does your TOC / FOC teach you to approach flashing double yellows.
(For the uninitiated, flashing double yellow aspects can be installed on the approach to a (relatively) high-speed turnout, provided the route is clear through the junction, so instead of successive signals being Green, Double Yellow, Single Yellow, Red, which - if the route is clear - then clears to a proceed aspect once a track circuit timer has ensured the train has slowed down, instead you get Flashing Double Yellow, Flashing Single Yellow, (steady) Single Yellow releasing to Green once the track circuit timer is passed. The flashing sequence informs the driver the route is set through the junction to the diverging line).

Your comment about "(relatively) high-speed turnouts" was true in the early days, with the likes of Didcot East, Weaver, Wooten Bassett but not any more. I'm aware of turnouts as low as 15 and one example (from a while back - might have changed) of flashing yellows into a bay platform - a particular case where PudseyBearHST's comment about not forgetting what lies beyond the signal is very important.

 

[L.M_DannyC]

From the passenger's perspective it's often intriguing how quickly (or not) a train slows on sighting a double yellow. On my local Snow Hill line for example, with a line speed of 75mph, trains used to approach Kidderminster at a fair pace from the north even on double yellow but often nowadays reduce speed dramatically and trundle into the station. Maybe the timetable is so slack there's no need to wear the brake discs out? Or maybe it's better to just ensure a slow enough speed in case the signal at the end of the platform turns red?

If you're talking about as recently as the last week or so there's currently a 20mph speed restriction just before the station coming in from the North due to the landslip which would explain the reduced speed coming into the station, better just to slow for the restriction and trundle into the station rather than powering up again.

 

[CW2]

Your comment about "(relatively) high-speed turnouts" was true in the early days, with the likes of Didcot East, Weaver, Wooten Bassett but not any more. I'm aware of turnouts as low as 15 and one example (from a while back - might have changed) of flashing yellows into a bay platform - a particular case where PudseyBearHST's comment about not forgetting what lies beyond the signal is very important.

I believe that post Colwich the rules were changed so that you can only receive flashing aspects if the route beyond the junction is clear for (at least) one section. So under those rules flashers into a bay platform would not be possible - unless there was a lot of track including an intermediate signal between the turnout and the bay.

 

[MichaelAMW]

I believe that post Colwich the rules were changed so that you can only receive flashing aspects if the route beyond the junction is clear for (at least) one section. So under those rules flashers into a bay platform would not be possible - unless there was a lot of track including an intermediate signal between the turnout and the bay.

Is the post-Colwich arrangement to risk assess each case? In other words, I don't think it is true that nowhere with flashing yellows is allowed to have a yellow at the junction signal that stays yellow and the signal beyond stays red. Happy to be corrected! Given what happened at Colwich, any such risk assesment would need to be interested in the consequences of a SPAD at that next signal. The other issue is that these things are not always applied restrospectively so I can well believe that you are correct but that I am also, in that there are older locations that don't conform.

 

[CW2]

Is the post-Colwich arrangement to risk assess each case? In other words, I don't think it is true that nowhere with flashing yellows is allowed to have a yellow at the junction signal that stays yellow and the signal beyond stays red. Happy to be corrected! Given what happened at Colwich, any such risk assesment would need to be interested in the consequences of a SPAD at that next signal. The other issue is that these things are not always applied restrospectively so I can well believe that you are correct but that I am also, in that there are older locations that don't conform.

Every resignalling scheme is fully risk assessed.
Post Colwich a number of flashing aspects were switched out at various points of the network, pending risk assessment and modification to the signal release arrangements.
Those locations where flashing aspects are now in use have been risk assessed, and I believe are fully compliant with the new arrangements.
I am not aware of any flashing aspects being used that are not "Colwich compliant," in other words, yes the new standards were enforced retrospectively, with the signalling either being amended or the flashing sequence disabled.
To be clear, the route has to be clear through the junction as far as a proceed aspect at the next section signal for flashing aspects to be activated (but see below).
If the junction cannot be cleared in time to set the route for the flashing aspect sequence, then the driver will receive a normal approach release from Red at the junction.

Take the example of Down Fast at Bletchley, where there is a flashing sequence for trains on the Down Fast to enter platform 5 (Down Fast Loop) at Milton Keynes. In order for the flashing sequence to be permitted there had to be another section signal between the junction and the stop signal at the platform - hence the great length of the loop.

 

[4F89]

Every resignalling scheme is fully risk assessed.
Post Colwich a number of flashing aspects were switched out at various points of the network, pending risk assessment and modification to the signal release arrangements.
Those locations where flashing aspects are now in use have been risk assessed, and I believe are fully compliant with the new arrangements.
I am not aware of any flashing aspects being used that are not "Colwich compliant," in other words, yes the new standards were enforced retrospectively, with the signalling either being amended or the flashing sequence disabled.
To be clear, the route has to be clear through the junction as far as a proceed aspect at the next section signal for flashing aspects to be activated (but see below).
If the junction cannot be cleared in time to set the route for the flashing aspect sequence, then the driver will receive a normal approach release from Red at the junction.

Take the example of Down Fast at Bletchley, where there is a flashing sequence for trains on the Down Fast to enter platform 5 (Down Fast Loop) at Milton Keynes. In order for the flashing sequence to be permitted there had to be another section signal between the junction and the stop signal at the platform - hence the great length of the loop.

So after the single flashing yellow and section, there must be at least 2 sections clear after the junction section? I'm trying to pinpoint what you are saying.

 

[MichaelAMW]

So after the single flashing yellow and section, there must be at least 2 sections clear after the junction section? I'm trying to pinpoint what you are saying.

Yes, me too - are you saying that you can never have a case where the junction signal stays at single yellow and the signal beyond be red, even, for example, where there is a full braking distance from the junction signal?

 

[CW2]

Yes, me too - are you saying that you can never have a case where the junction signal stays at single yellow and the signal beyond be red, even, for example, where there is a full braking distance from the junction signal?

To be honest I'm not 100% sure. I'm not a signal engineer myself, merely been involved in designing layouts with the help of signalling engineers (of which my example at MK was one).

I'll see if I can dig out the relevant advice on the NR website.

EDIT:

I can't get into the NR standards without signing up and paying hard cash. However I did find this elsewhere on the net:

GK/RT0045 issue 3 para 5.2.3.6:

"A flashing aspect sequence shall only be displayed when the approaching train is detected to be in a position that is compatible with the required reading time of the junction distant signal that displays the flashing single yellow aspect and one of the following applies:
a) The first signal beyond the diverging junction is a controlled stop signal that is either one of the following:
i) Displaying an OFF aspect.
ii) Displaying an ON aspect and a forward route is set.
iii) Displaying an ON aspect at the end of a loop line or platform line where all trains are expected to stop.
b) The first signal beyond the diverging junction is an automatic signal.
c) The first signal beyond the diverging junction is an isolated distant signal."

So plenty of variety there. No wonder I was confused!

NOTE: this posting dated from 2014, so standards may have moved on since then.

 

[4F89]

I was asking as I know of a few places where you can be flashed into a loop which doesn't step up from the yellow, although it does have a long distance to the red.

 

[CW2]

I was asking as I know of a few places where you can be flashed into a loop which doesn't step up from the yellow, although it does have a long distance to the red.

I guess that would come under "iii) Displaying an ON aspect at the end of a loop line or platform line where all trains are expected to stop."

 

[Efini92]

What's the SG button?

If you press it under Piccadilly’s panel, it tells the signaller you’re happy to sit there for 20 minutes whilst they run everything around you.

 

[satisnek]

From the passenger's perspective it's often intriguing how quickly (or not) a train slows on sighting a double yellow. On my local Snow Hill line for example, with a line speed of 75mph, trains used to approach Kidderminster at a fair pace from the north even on double yellow but often nowadays reduce speed dramatically and trundle into the station. Maybe the timetable is so slack there's no need to wear the brake discs out? Or maybe it's better to just ensure a slow enough speed in case the signal at the end of the platform turns red?

The reason for this is that the double yellow you mention was a 3-aspect distant (as discussed in another thread), the purpose of which was to provide an unrestricted approach for terminating trains. The next signal (Kidderminster Junction's outer home) was a 3-aspect colour light, which would show a single yellow, and after that was the semaphore inner home (at danger) which was some distance beyond the platform. Therefore, a terminating train could come bowling into the station in the same manner as a Worcester-bound service running under clear signals and even if the driver overshot the platform (yes, it did happen!), there was no possibility of a SPAD.

Today the line is equipped with 3-aspect LED signals (no double yellows). One is situated a short distance beyond the site of the old distant and the next is at the platform end, which will be showing red for terminating trains. Hence the much more cautious approach!

 

[moggie]

To be honest I'm not 100% sure. I'm not a signal engineer myself, merely been involved in designing layouts with the help of signalling engineers (of which my example at MK was one).

I'll see if I can dig out the relevant advice on the NR website.

EDIT:

I can't get into the NR standards without signing up and paying hard cash. However I did find this elsewhere on the net:

GK/RT0045 issue 3 para 5.2.3.6:

"A flashing aspect sequence shall only be displayed when the approaching train is detected to be in a position that is compatible with the required reading time of the junction distant signal that displays the flashing single yellow aspect and one of the following applies:
a) The first signal beyond the diverging junction is a controlled stop signal that is either one of the following:
i) Displaying an OFF aspect.
ii) Displaying an ON aspect and a forward route is set.
iii) Displaying an ON aspect at the end of a loop line or platform line where all trains are expected to stop.
b) The first signal beyond the diverging junction is an automatic signal.
c) The first signal beyond the diverging junction is an isolated distant signal."

So plenty of variety there. No wonder I was confused!

NOTE: this posting dated from 2014, so standards may have moved on since then.

Flashing aspects at the time of the Colwich collision were in their infancy (and were at this particular installation) and as I recall without looking into the precise circumstances were implemented at Colwich such that the flashing sequence was given for the first of two successive diverging junctions. In the case of Colwich the first in direction of travel was from the Dn Fast to the Dn Slow but NOT the subsequent divergence for the Dn Stoke Line situated in the next signal section. The driver mistakenly believed the flashing sequence implied they were clear to proceed throughout the junction.

The specific requirements in the signalling principle above I recall were brought in after a SPAD incident at Swinton curve involving a cross country train. No doubt this particular incident was not an isolated one across the network. It's the ol' cherry of providing a contradictory 'hurry up' aspect sequence immediately followed with an 'unexpected' Stop command and then relying on the driver to (always) accurately assimilate the information. I think the amended principle introduced post Swinton was an infinitely sensible one.

 

[peteb]

If you're talking about as recently as the last week or so there's currently a 20mph speed restriction just before the station coming in from the North due to the landslip which would explain the reduced speed coming into the station, better just to slow for the restriction and trundle into the station rather than powering up again.

Aha forgot that landslip by the Railway Train pub Offmore Road! They were lucky the car didnt roll down the cutting, it was left teetering on the edge!

The reason for this is that the double yellow you mention was a 3-aspect distant (as discussed in another thread), the purpose of which was to provide an unrestricted approach for terminating trains. The next signal (Kidderminster Junction's outer home) was a 3-aspect colour light, which would show a single yellow, and after that was the semaphore inner home (at danger) which was some distance beyond the platform. Therefore, a terminating train could come bowling into the station in the same manner as a Worcester-bound service running under clear signals and even if the driver overshot the platform (yes, it did happen!), there was no possibility of a SPAD.

Today the line is equipped with 3-aspect LED signals (no double yellows). One is situated a short distance beyond the site of the old distant and the next is at the platform end, which will be showing red for terminating trains. Hence the much more cautious approach!

Thanks for the clarification.

 

[MichaelAMW]

To be honest I'm not 100% sure. I'm not a signal engineer myself, merely been involved in designing layouts with the help of signalling engineers (of which my example at MK was one).

I'll see if I can dig out the relevant advice on the NR website.

EDIT:

I can't get into the NR standards without signing up and paying hard cash. However I did find this elsewhere on the net:

GK/RT0045 issue 3 para 5.2.3.6:

"A flashing aspect sequence shall only be displayed when the approaching train is detected to be in a position that is compatible with the required reading time of the junction distant signal that displays the flashing single yellow aspect and one of the following applies:
a) The first signal beyond the diverging junction is a controlled stop signal that is either one of the following:
i) Displaying an OFF aspect.
ii) Displaying an ON aspect and a forward route is set.
iii) Displaying an ON aspect at the end of a loop line or platform line where all trains are expected to stop.
b) The first signal beyond the diverging junction is an automatic signal.
c) The first signal beyond the diverging junction is an isolated distant signal."

So plenty of variety there. No wonder I was confused!

NOTE: this posting dated from 2014, so standards may have moved on since then.

Thanks for this. With some mild wracking of brains I suspect that the examples I can think of which might allow a following signal to be at red are probably of form (ii) or (iii). Presumably (ii) would allow for that signal beyond the junction to be approach controlled so, although it will (initially) remain at red, the section beyond is safely clear.

 

[CW2]

Thanks for this. With some mild wracking of brains I suspect that the examples I can think of which might allow a following signal to be at red are probably of form (ii) or (iii). Presumably (ii) would allow for that signal beyond the junction to be approach controlled so, although it will (initially) remain at red, the section beyond is safely clear.

Yes,that sounds correct to me. However the circumstances in which we wish to encourage a driver to clear the junction as quickly as possible (by providing flashing aspects) whilst simultaneously instructing him / her to slow down (by means of approach control on the subsequent signal) might make for an interesting risk assessment.

 

[MichaelAMW]

Flashing aspects at the time of the Colwich collision were in their infancy (and were at this particular installation) and as I recall without looking into the precise circumstances were implemented at Colwich such that the flashing sequence was given for the first of two successive diverging junctions. In the case of Colwich the first in direction of travel was from the Dn Fast to the Dn Slow but NOT the subsequent divergence for the Dn Stoke Line situated in the next signal section. The driver mistakenly believed the flashing sequence implied they were clear to proceed throughout the junction.

In fact, there was no divergence, in the signalling sense, at the next signal. i.e. the main route was to the Stoke line from the down slow; there was a crossover back to the down main towards Stafford. Otherwise, what you say is right.

There's a map at the end of this: https://www.railwaysarchive.co.uk/documents/DoT_Colwich1988.pdf

As commented there, and very much related to your point, the flashing yellows were for a crossover but not for the geographical junction. From page 15:

"While the extension of the use of flashing yellow aspects was in itself perfectly safe, I have no doubt
that their extended meaning should have been more clearly explained, particularly where flashing Yellow
aspects lead to a crossover which in turn leads to a signal controlling a true diverging junction, as was the case
at Colwich at the time of the accident."

Yes,that sounds correct to me. However the circumstances in which we wish to encourage a driver to clear the junction as quickly as possible (by providing flashing aspects) whilst simultaneously instructing him / her to slow down (by means of approach control on the subsequent signal) might make for an interesting risk assessment.

Indeed, but, to pick up one of your earlier points, that does provide a very speedy way of getting trains into platform loops. Ideally, I guess, you want the turnout speed to be fast enough when combined with flashing yellows that the driver can simply make a normal approach to the platform and, in a sense, not actually have to worry about the turnout speed at all. In the past that arrangement - signal at the end of the platform staying at red - was certainly in place at Lancaster and Reading, just off the top of my head.

 

[43066]

So do you consider a flashing double yellow as a cautionary signal, or do you treat is as a Green-with-extra-information?
How does your TOC / FOC teach you to approach flashing double yellows.
(For the uninitiated, flashing double yellow aspects can be installed on the approach to a (relatively) high-speed turnout, provided the route is clear through the junction, so instead of successive signals being Green, Double Yellow, Single Yellow, Red, which - if the route is clear - then clears to a proceed aspect once a track circuit timer has ensured the train has slowed down, instead you get Flashing Double Yellow, Flashing Single Yellow, (steady) Single Yellow releasing to Green once the track circuit timer is passed. The flashing sequence informs the driver the route is set through the junction to the diverging line).

Strictly speaking a flashing double yellow is “green with extra information” - that information being that you’re going to be turning onto the highest speed diverging route at the forthcoming junction. Knowing what that speed is comes down to route knowledge.

Service braking distance to the red beyond the junction (which should never be assumed to step up) starts from the flashing single yellow.

Every resignalling scheme is fully risk assessed.
Post Colwich a number of flashing aspects were switched out at various points of the network, pending risk assessment and modification to the signal release arrangements.
Those locations where flashing aspects are now in use have been risk assessed, and I believe are fully compliant with the new arrangements.
I am not aware of any flashing aspects being used that are not "Colwich compliant," in other words, yes the new standards were enforced retrospectively, with the signalling either being amended or the flashing sequence disabled.
To be clear, the route has to be clear through the junction as far as a proceed aspect at the next section signal for flashing aspects to be activated (but see below).
If the junction cannot be cleared in time to set the route for the flashing aspect sequence, then the driver will receive a normal approach release from Red at the junction.

Take the example of Down Fast at Bletchley, where there is a flashing sequence for trains on the Down Fast to enter platform 5 (Down Fast Loop) at Milton Keynes. In order for the flashing sequence to be permitted there had to be another section signal between the junction and the stop signal at the platform - hence the great length of the loop.

I’m afraid you’re confusing absolute block with TCB. Section signals are an AB concept and are stop signals.

I used to sign a location where the sequence would regularly be flashing double yellow, flashing single yellow, steady single yellow, red (protecting exits from bay platforms). Absolutely no requirement for the red to step up, or for the section beyond it to be clear.

 

[contrex]

Send Green

I thought you meant Seer Green for a minute.

 

[Strat-tastic]

If you press it under Piccadilly’s panel, it tells the signaller you’re happy to sit there for 20 minutes whilst they run everything around you.

What's Piccadilly's panel?

 

[Efini92]

What's Piccadilly's panel?

When your in the area covered by Manchester Piccadilly power box

 

[Hincappie]

This has made for some interesting reading. Thank you to everyone who added serious and knowledgeable responses and opinions here. Much appreciated.