Double flashing lights at Merstham station. Normal?

[Highlandspring]

Strictly flashing aspects occult, that is they darken, thus if the flasher unit fails it will cause the aspect to revert to a steady aspect and therefore a more restrictive state.

To be super pedantic the term occulting simply describes any rythmically phased light which is illuminated for a longer period than it is dark/obscured/dimmed; it doesn’t relate to whether or not the light is made completely dark or just dimmed. Flashing describes a rhythmically phased light which is dark/obscured/dimmed for longer than it is illuminated (for completeness the term isophase is used for a light where both dark and light phases are of equal length).

 

[Crossover]

Very common.

It’s an indication to the driver that, at a forthcoming complex junction, they will be taking the highest speed diverging route and will be followed with: single flashing yellow; single solid yellow with junction indicator; red (although the solid yellow willl likely step up to green on approach).

Interesting - I had thought the flashing indication was lowest. The signal just beyond Mirfield p1 (Leeds bound) is green where the route is set for Dewsbury and flashing yellow for Wakefield services. I don't know the linespeeds but would have guessed the Wakefield diversion to be the slower one due to the crossover and overall slightly "odd" junction layout.

 

[John R]

Fair enough, I'm not a driver so I have to go on what others have told me and the unfortunate consequence of that is you don' know when you're being told a load of old tosh!

Maybe best then if you confine statements in your posts to those where you know your facts, rather than rely on others, especially if that information has come from other posts on this or similar fora. Else you will quickly get a reputation for similarly spouting tosh and wibble.

 

[hexagon789]

Maybe best then if you confine statements in your posts to those where you know your facts, rather than rely on others, especially if that information has come from other posts on this or similar fora. Else you will quickly get a reputation for similarly spouting tosh and wibble.

Doesn't stop most people

That is to say other members, to clarify the point.

 

[John R]

Flashing yellows were introduced in the mid seventies with the introduction of HST's which had enhanced braking characteristics that enabled them to stop from 125mph within signal spacing that was appropriate for 100mph trains. This could lull drivers into a false sense of security if a double yellow was showing in advance of a single yellow approach controlled junction rather than with a red two sections ahead. The whole subject of approach control is very clearly described in the attached link, much better than I could do, and I commend it to those who want to know more.

https://www.davros.org/rail/signalling/articles/junctions.html

 

[driver_m]

By the way to the OP. Nice name!

 

[Bromley boy]

Flashing yellows were introduced in the mid seventies with the introduction of HST's which had enhanced braking characteristics that enabled them to stop from 125mph within signal spacing that was appropriate for 100mph trains. This could lull drivers into a false sense of security if a double yellow was showing in advance of a single yellow approach controlled junction rather than with a red two sections ahead. The whole subject of approach control is very clearly described in the attached link, much better than I could do, and I commend it to those who want to know more.

https://www.davros.org/rail/signalling/articles/junctions.html

Very detailed and informative, many thanks for posting.

Splitting distances are interesting, I wonder if there are any still in use...

 

[GW43125]

Splitting distances are interesting, I wonder if there are any still in use...

There's a couple between Reading and Paddington where flashers are unsuitable for whatever reason. Airport Jn springs to mind.

 

[Tomnick]

Interesting - I had thought the flashing indication was lowest. The signal just beyond Mirfield p1 (Leeds bound) is green where the route is set for Dewsbury and flashing yellow for Wakefield services. I don't know the linespeeds but would have guessed the Wakefield diversion to be the slower one due to the crossover and overall slightly "odd" junction layout.

Towards Dewsbury is the ‘straight’, unrestricted route. Towards Wakefield is the highest speed (and indeed only) diverging route. Any subsequent, lower speed, diverging routes would almost certainly require approach release from red.

 

[Chris Hamilton]

With double flashing yellows does one need to slow down? I ask because i have seen them at the end of platform 1 at Berrylands when the gap between trains seems to me to be a reasonable distance. One would probably have to slow down into Surbtion anyway of course.

Short answer, yes. Long answer, yes, for two reasons.

Firstly, the diverging line ahead will have a lower line speed than the main route.

Secondly, I have investigated at least one SPAD, where a driver treated all the aspects (double flash, single flash, single steady) as if he was approaching a green. Normally, the last aspect in the sequence would step up from red to green (the signal following the Junction), before it had even come into his view (it was around a slight bend and partly obscured by a bridge) and he would apply power through it. On this occasion, because of a freight that had stopped ahead of him, it didn’t, and he applied power before seeing the final red aspect, straight into an occupied section and passed the signal at red by a carriage length.

On a technical note, by design, if either of the flashing signals cannot flash for whatever reason (failed flasher, faulty signalling module etc), the route can still be given, but the signalling system will revert to “approach control” where the normally flashing aspects will stay steady, and the normally single steady yellow will instead stay at red until the train is occupying the berth track circuit for it, before increasing to a proceed aspect. This is to bring the train to an almost complete stand before the diverging route, and was standard practice before the flashing yellow was developed for high speed turnouts.

 

[infobleep]

Short answer, yes. Long answer, yes, for two reasons.

Firstly, the diverging line ahead will have a lower line speed than the main route.

Secondly, I have investigated at least one SPAD, where a driver treated all the aspects (double flash, single flash, single steady) as if he was approaching a green. Normally, the last aspect in the sequence would step up from red to green (the signal following the Junction), before it had even come into his view (it was around a slight bend and partly obscured by a bridge) and he would apply power through it. On this occasion, because of a freight that had stopped ahead of him, it didn’t, and he applied power before seeing the final red aspect, straight into an occupied section and passed the signal at red by a carriage length.

On a technical note, by design, if either of the flashing signals cannot flash for whatever reason (failed flasher, faulty signalling module etc), the route can still be given, but the signalling system will revert to “approach control” where the normally flashing aspects will stay steady, and the normally single steady yellow will instead stay at red until the train is occupying the berth track circuit for it, before increasing to a proceed aspect. This is to bring the train to an almost complete stand before the diverging route, and was standard practice before the flashing yellow was developed for high speed turnouts.

Very interesting. Incidentally It never feels as if the section between Berrylands and Surbtion is high speed whenever I might have been on it. Trains that stop at Berrylands also stop at Surbtion, unless there is some technical reasons why they cannot.

 

[Chris Hamilton]

Very interesting. Incidentally It never feels as if the section between Berrylands and Surbtion is high speed whenever I might have been on it. Trains that stop at Berrylands also stop at Surbtion, unless there is some technical reasons why they cannot.

It doesn’t need to be high speed, per-say, the decision whether or not to use flashing yellow aspects is based on the differential speed between the main route and the diverging route. High speed turnout, in this case, in this usage means one which doesn’t require a dramatic reduction in speed in order to take it. Say 75mph line with a 50mph turnout. The exact ratio between them to justify it would be for a signalling designer to answer (I’d need to trek through a standard to find it).

Signalling design needs to take into account changes to the stopping pattern and services not normally seen, so they cannot assume that every train for the life of the system will set off towards that Junction from a standing start. Using approach control instead of flashing aspects severely restricts the flow of traffic. At one junction near me, during a failure of the flashing system, every single train taking the diverging route incurred nearly 3 minutes of delays because of the need to come to nearly a complete stand.

They also need to account for non-passenger services that wouldnt stop at either station, however unlikely it seems.

 

[The Planner]

There's a couple between Reading and Paddington where flashers are unsuitable for whatever reason. Airport Jn springs to mind.

There were some at Tilehurst too I think, but these may have gone as part of Reading. Also there is one on the down at Bicester South for the chord down to Gavray Jn

 

[Trackman]

Short answer, yes. Long answer, yes, for two reasons.

Firstly, the diverging line ahead will have a lower line speed than the main route.

Secondly, I have investigated at least one SPAD, where a driver treated all the aspects (double flash, single flash, single steady) as if he was approaching a green. Normally, the last aspect in the sequence would step up from red to green (the signal following the Junction), before it had even come into his view (it was around a slight bend and partly obscured by a bridge) and he would apply power through it. On this occasion, because of a freight that had stopped ahead of him, it didn’t, and he applied power before seeing the final red aspect, straight into an occupied section and passed the signal at red by a carriage length.

On a technical note, by design, if either of the flashing signals cannot flash for whatever reason (failed flasher, faulty signalling module etc), the route can still be given, but the signalling system will revert to “approach control” where the normally flashing aspects will stay steady, and the normally single steady yellow will instead stay at red until the train is occupying the berth track circuit for it, before increasing to a proceed aspect. This is to bring the train to an almost complete stand before the diverging route, and was standard practice before the flashing yellow was developed for high speed turnouts.

Sounds similar to the Colwich rail crash, the driver was expecting a green aspect.

 

[Jimini]

Does the country end of Guildford still have one for the North Downs route? Been about 20 years since I spotted that one (first one I saw incidentally).

 

[GW43125]

Does the country end of Guildford still have one for the North Downs route? Been about 20 years since I spotted that one (first one I saw incidentally).

Was certainly still there last year. Most likely still is as it’s a 40mph turnout from a 70mph line

 

[Crossover]

Towards Dewsbury is the ‘straight’, unrestricted route. Towards Wakefield is the highest speed (and indeed only) diverging route. Any subsequent, lower speed, diverging routes would almost certainly require approach release from red.

Ah - I think I have misunderstood. So a flashing aspect would signify a drop in speed for the turnout but that it was the highest speed diverging route (or only in this case)? Would that mean that any other diverging route would just be under 'normal' approach control?

 

[Tomnick]

Ah - I think I have misunderstood. So a flashing aspect would signify a drop in speed for the turnout but that it was the highest speed diverging route (or only in this case)? Would that mean that any other diverging route would just be under 'normal' approach control?

Yes, spot on. There’s no need for any control on the fastest route, the ‘straight’ route, because the driver doesn’t need to brake specially for the junction. The flashing yellows for the highest speed diverging route tell the driver that’s the route’s set through the junction so he’ll be braking for that and for the possibility of the first signal behind the junction being at danger. If the flashing yellow sequence could also apply to a lower speed diverging route, there’s a clear risk that the driver of a train, perhaps expecting the higher speed divergence, might not be able to slow down enough upon sighting the junction signal and the route indication shown there.

 

[Nippy]

There were some at Tilehurst too I think, but these may have gone as part of Reading. Also there is one on the down at Bicester South for the chord down to Gavray Jn

The one approaching Gavray has a splitting outer distant as well!

We have them at Acton West UM-UR, Airport Jn DM-DA, Stockley Jn UR-UM on the desks I sign.

 

[NaZzAtAzEr]

By the way to the OP. Nice name!

Thanks, but a mod just messaged me asking me to change it

 

[daikilo]

A red with a subsidiary (two white lights) would also be a proceed aspect.

Technically I think not. The aspect is red so is not a proceed. The subsidiary white lights when the upper light is lit is an authorisation to pass for a specific purpose like a shunt or running into an occupied platform, the only thing the driver can be sure of is that there won't be a train coming towards him, but there may be a train already in the section.

 

[Crossover]

Yes, spot on. There’s no need for any control on the fastest route, the ‘straight’ route, because the driver doesn’t need to brake specially for the junction. The flashing yellows for the highest speed diverging route tell the driver that’s the route’s set through the junction so he’ll be braking for that and for the possibility of the first signal behind the junction being at danger. If the flashing yellow sequence could also apply to a lower speed diverging route, there’s a clear risk that the driver of a train, perhaps expecting the higher speed divergence, might not be able to slow down enough upon sighting the junction signal and the route indication shown there.

Thanks @Tomnick

 

[ComUtoR]

Technically I think not. The aspect is red so is not a proceed.

It is not to be taken in isolation. Red on its own would be stop. Red+Position light is proceed at caution.

the only thing the driver can be sure of is that there won't be a train coming towards him,

There can be movements in the section ahead. If a unit was coming towards me I wouldn't be surprised and neither would it be the first time.

but there may be a train already in the section.

You are often given a position light to enter unoccupied sections due to the way signalling works. Proceed at caution and be prepared to stop short of ANY obstruction. Train or otherwise.

 

[edwin_m]

Technically I think not. The aspect is red so is not a proceed. The subsidiary white lights when the upper light is lit is an authorisation to pass for a specific purpose like a shunt or running into an occupied platform, the only thing the driver can be sure of is that there won't be a train coming towards him, but there may be a train already in the section.

https://www.rssb.co.uk/rgs/standards/GKGN0802 Iss 1.pdf

Proceed Aspect Any Signal Aspect which permits the driver to pass the Signal.

This is from the Glossary of Signalling Terms. Curiously, although the Rule Book glossary mentions it in other definitions, it doesn't define "proceed aspect". This definition would certainly include a subsidiary, and it is equally arguable that other aspects have a "specific purpose", such as a single yellow authorising movement as far as the next main stop signal or buffer stop.

Incidentally a subsidiary also confirms to the driver that "worked" points up to the limit of authority are correctly set and will not change as the train approaches them.

 

[Bromley boy]

Technically I think not. The aspect is red so is not a proceed. The subsidiary white lights when the upper light is lit is an authorisation to pass for a specific purpose like a shunt or running into an occupied platform, the only thing the driver can be sure of is that there won't be a train coming towards him, but there may be a train already in the section.

I’ve proceeded past many a red, with the corresponding dummy illuminated . Even a few reds without a dummy (but with authority!)

A good definition of a proceed aspect is probably any aspect you can pass without direct authority from the signaller/TBW ticket (if you have to be talked past it, it’s obviously not a proceed aspect).

EDIT: edwin_m beat me to it!