Flashing greens.

[cf111]

Quite a boring question, but here goes.

On part of the ECML, signals can display a flashing green aspect, which I'm told is relic from the testing of the InterCity 225, and signified that trains were permitted to run at up to 140 MPH.

If the signaller wanted to check a train down to stop (for example), would the signals work in this order today:

Flashing Green > Steady Green > Double Yellow > Single Yellow > Red.

Or does the "Flashing Green" aspect simply replace the "Steady Green" (i.e. the first signal would display flashing green and the one after would display double yellow) as no trains are permitted to run any faster than 125 MPH?

Apologies if the above isn't clear!

 

[Tomnick]

The sequence is indeed FG>G>YY>Y>R - the flashing green is provided purely to allow trains to run at speeds in excess of 125mph, safe in the knowledge that the next signal is showing at least a steady green (and they'll be able to get down to 125mph by the YY if they pass a steady green). It's all irrelevant, now that nothing's allowed to run over 125mph, but the signalling remains.

 

[yorkie]

More info here: http://www.railforums.co.uk/showthread.php?p=515143#post515143

... testing was done on the ECML in the Stoke Bank area (I think) where a flashing green aspect was added to some signals to authorise 140mph running. However the results of the trial were that it was felt that drivers couldn't be expected to reliably read the signal and react at those speeds hence for anything over 125 in this country you have to have in-cab signalling.....

 

[cf111]

Thank you both.

 

[Muzer]

So are signallers nowadays allowed to "adverse change of aspect" drivers from flashing green to green (ie bring a signal 4 in front of the driver to danger) safe in the knowledge that there are no longer any >125mph tests?

 

[MarkyT]

So are signallers nowadays allowed to "adverse change of aspect" drivers from flashing green to green (ie bring a signal 4 in front of the driver to danger) safe in the knowledge that there are no longer any >125mph tests?

Its always safe to replace a signal to red even with a train approaching due to a feature of interlocking called approach locking. This keeps routes through junctions locked in position beyond the replaced signal if any approaching train is close enough to see a change to a cautionary aspect as a result. If the train then overuns the replaced signal at red due to insufficient warning, a safe route is preserved with no conflicting routes being able to be set. Clearly such late signal replacement should only be carried out in an emergency. For flashing greens it might be that approach locking extends out to the sighting point of the steady green, instead of the double yellow as in normal 4-aspect signalling.

 

[GB]

Not everywhere is equipped with approach locking as the signaller at Morton-on-Lugg found out a few years ago.

 

[MarkyT]

Not everywhere is equipped with approach locking as the signaller at Morton-on-Lugg found out a few years ago.

Very true. I should have qualified my previous statement. Approach locking is standard for TCB equipped lines, but is only 'patchy' in AB areas where much more reliance is placed on the signaller following procedure correctly. Mind you I don't think there's any AB remaining on the ECML where the flashing greens are!

 

[Railsigns]

Approach locking isn't always comprehensive, so there may be no 'look back' to the sighting point of the first caution aspect; there will just be a timed release. And there is no need for approach locking in areas of plain line and automatic signals.

 

[Muzer]

Its always safe to replace a signal to red even with a train approaching due to a feature of interlocking called approach locking. This keeps routes through junctions locked in position beyond the replaced signal if any approaching train is close enough to see a change to a cautionary aspect as a result. If the train then overuns the replaced signal at red due to insufficient warning, a safe route is preserved with no conflicting routes being able to be set. Clearly such late signal replacement should only be carried out in an emergency. For flashing greens it might be that approach locking extends out to the sighting point of the steady green, instead of the double yellow as in normal 4-aspect signalling.

Indeed - but what I intended by my question is, is it acceptable in normal circumstances and not just an emergency to bring a signal in front of a driver from a flashing green to a green? (Actually, come to think of it, how much route cancelling is acceptable in normal circumstances even if it won't lead to an adverse change of aspect? Playing SimSig you're only penalised if it causes the driver to see a more restrictive aspect than they should/a change of aspect to more restrictive, but obviously SimSig isn't always perfectly accurate to real life )

 

[carriageline]

FG->G is still a valid sequence of aspects, pulling up on a FG to a G will cause him to see a improper sequence.
A lot of routes get cancelled every day, several sections in front of drivers and they never know, mostly when regulating trains. The route only "times" out when the train is close enough that he could see a signal change in front of him, some installations are a pain, if it's busy and waiting for a route to time out, you can sometimes have a blank and try recancelling it, causing the two minute time out counter to start again!!

A driver should never see a signal change in front of him (unless it is a few signals ahead and he is 'reading through'), unless the sig has his permission, or an emergency/failure etc. if it does happen, it involves paper work, checking the driver is ok etc etc, and the delays soon add up!!

I would be suprised if the function was still on the panels for the flashing greens, when I was in peterborough box, and kings cross box for a visit I never saw anything like that, nor was it mentioned!


Sent from my iPhone using Tapatalk

 

[Tomnick]

There's nothing, as far as I'm aware, on the panel - the signals will just step up to flashing green themselves once the next signal is at least steady green, just as they'll step up from YY to G with no intervention. They definitely still clear to a flashing green when they're able to do so!

 

[edwin_m]

The route only "times" out when the train is close enough that he could see a signal change in front of him, some installations are a pain, if it's busy and waiting for a route to time out, you can sometimes have a blank and try recancelling it, causing the two minute time out counter to start again!!

This is only true where "comprehensive approach locking release" is provided, which isn't everywhere as it is quite tricky and expensive to do. Otherwise the route times out whether there is a train approaching or not.

On all the installations I'm aware of, the panel/screen indication will show flashing red while the ALR timer is running. The actual signal does not do this, just showing a steady red.

 

[MarkyT]

This is only true where "comprehensive approach locking release" is provided, which isn't everywhere as it is quite tricky and expensive to do. Otherwise the route times out whether there is a train approaching or not.

On all the installations I'm aware of, the panel/screen indication will show flashing red while the ALR timer is running. The actual signal does not do this, just showing a steady red.

Quite right about comprehensive approach locking, actually rare in newer installations even on the busiest lines ISTR, as mis-routing is considered to be rarer today, especially with automated route setting (ARS). One place where comprehensive is usually provided by default however is at level crossings, so the road can be reopened quickly if there's no train about - important if there were emergency services' vehicles trapped for example.

Traditional panels only showed red (flashing when approach locked) or green for 'better than red' indications. IECC screens, by contrast, show detailled aspects: yellow, double yellow, flashing yellow(s) and green, so I would expect that they could and might show a flashing green, if there are any in such areas of control.