Flashing green aspects

Status
Not open for further replies.

najaB

Veteran Member
Joined
28 Aug 2011
Messages
23,991
Location
Scotland
When flashing greens were installed to allow 91/Mk.4s to operate at 140mph, did that make steady green a restrictive aspect for those trains?
 
Last edited:
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R

RailUK Forums

roversfan2001

Established Member
Joined
19 Feb 2016
Messages
1,414
Location
Lancashire
It meant to run at 125mph didn't it? If it slows them from 140mph to 125mph then yes it is somewhat restrictive.
 

najaB

Veteran Member
Joined
28 Aug 2011
Messages
23,991
Location
Scotland
It meant to run at 125mph didn't it? If it slows them from 140mph to 125mph then yes it is somewhat restrictive.
Sorry, what I meant was if drivers were to treat them as if they were triple yellows and to expect a double yellow ahead.

Sent from my Nexus 4 using Tapatalk
 

Philip Phlopp

Established Member
Joined
31 May 2015
Messages
3,004
Sorry, what I meant was if drivers were to treat them as if they were triple yellows and to expect a double yellow ahead.

Sent from my Nexus 4 using Tapatalk

No, with the five aspect signalling system, you should expect to see either a flashing green or a single green aspect ahead, if you see the single green aspect ahead, you drop the speed to 125mph.

The five aspect signalling system effectively tells you what the signal aspect is in the block ahead a section earlier than with the four aspect system - if you don't get a flashing green but a single green, that's because the next block is at double yellow. You don't know you've got a double yellow until you see it with the four aspect system.

It was all basically a way to extend out the braking curve for 140mph stock whilst retaining the issues of having a human at the helm. An IC225 set will stop from 140mph within two signalling sections but it won't be comfortable for passengers, it really needs three signalling sections.
 
Last edited:

Class 170101

Established Member
Joined
1 Mar 2014
Messages
6,647
Class 91s need the extra distance to brake comfortably from 140mph to a stand but what about Pendolinos?

Could they come to a stand upon seeing a double yellow at 140mph to the red two signals later and comfortably?
 

D1009

Established Member
Joined
22 Feb 2012
Messages
3,166
Location
Stoke Gifford
Isn't the discussion a bit irrelevant as the safety authorities have decided that you can't exceed 125 mph without cab signalling.
 

yorkie

Forum Staff
Staff Member
Administrator
Joined
6 Jun 2005
Messages
53,206
Location
Yorkshire
Sorry, what I meant was if drivers were to treat them as if they were triple yellows and to expect a double yellow ahead.
That's what green signals, in 4 aspect areas, always signify!;) So it's no different in that respect. If a driver sees a green in a 4 aspect area, then it means that the next 3 blocks are clear.
--- old post above --- --- new post below ---
Isn't the discussion a bit irrelevant as the safety authorities have decided that you can't exceed 125 mph without cab signalling.
Yes it is.
 

cjmillsnun

Established Member
Joined
13 Feb 2011
Messages
3,050
Class 91s need the extra distance to brake comfortably from 140mph to a stand but what about Pendolinos?

Could they come to a stand upon seeing a double yellow at 140mph to the red two signals later and comfortably?

From what I gathered from Philip Phlopp the 225 sets can stop from 140mph from a double yellow comfortably, the issue is passenger comfort as it would be severe braking. I doubt Pendolinos would be any different in that regard.
 

Philip Phlopp

Established Member
Joined
31 May 2015
Messages
3,004
Class 91s need the extra distance to brake comfortably from 140mph to a stand but what about Pendolinos?

Could they come to a stand upon seeing a double yellow at 140mph to the red two signals later and comfortably?

I think there's a couple of drivers on here who were involved in the testing and type approval who might be better placed to comment on the whole thing.
 

najaB

Veteran Member
Joined
28 Aug 2011
Messages
23,991
Location
Scotland
Sorry, what I meant was if drivers were to treat them as if they were triple yellows and to expect a double yellow ahead.
That's what green signals, in 4 aspect areas, always signify!;) So it's no different in that respect.
Interesting. In my head I always thought a green means "Expect a green but be prepared for double-yellow".
 

Railsigns

Established Member
Joined
15 Feb 2010
Messages
1,764
In my head I always thought a green means "Expect a green but be prepared for double-yellow".

Goodness me, no. Telling drivers to "expect a green" at a signal that might be displaying a caution aspect would be asking for trouble.
 

najaB

Veteran Member
Joined
28 Aug 2011
Messages
23,991
Location
Scotland
Goodness me, no. Telling drivers to "expect a green" at a signal that might be displaying a caution aspect would be asking for trouble.
Yeah, I can see the logic there, but if you're expecting a cautionary aspect would you open the taps after when the line speed increases after passing a green? I suppose I'm reading too much into the word 'expect'.
 

Railsigns

Established Member
Joined
15 Feb 2010
Messages
1,764
Yeah, I can see the logic there, but if you're expecting a cautionary aspect would you open the taps after when the line speed increases after passing a green?

Yes, why not? The next signal beyond the permissible speed increase would have to be spaced at full braking distance - from the higher speed - to the relevant stop signal (two signals ahead in 4-aspect territory).
 

455driver

Veteran Member
Joined
10 May 2010
Messages
11,332
Class 91s need the extra distance to brake comfortably from 140mph to a stand but what about Pendolinos?

Could they come to a stand upon seeing a double yellow at 140mph to the red two signals later and comfortably?

As 91s dont run at 140mph it doesnt really matter.
 
Last edited:

Tomnick

Established Member
Joined
10 Jun 2005
Messages
5,500
Yes, why not? The next signal beyond the permissible speed increase would have to be spaced at full braking distance - from the higher speed - to the relevant stop signal (two signals ahead in 4-aspect territory).
Just a thought that'd been niggling away for a while - how's that work at, say, Woolmer Green Jn where a green on the Up Slow (3-aspect signal protecting the junction) can read to a single yellow (in a 4-aspect sequence if approached from the Up Fast), which would then give inadequate braking distance to the red if a train off the slow was able to accelerate to (nearly) linespeed before sighting the yellow? Is there an assumption made about the best possible acceleration characteristics in this sort of case?
 

Railsigns

Established Member
Joined
15 Feb 2010
Messages
1,764
Just a thought that'd been niggling away for a while - how's that work at, say, Woolmer Green Jn where a green on the Up Slow (3-aspect signal protecting the junction) can read to a single yellow (in a 4-aspect sequence if approached from the Up Fast), which would then give inadequate braking distance to the red if a train off the slow was able to accelerate to (nearly) linespeed before sighting the yellow? Is there an assumption made about the best possible acceleration characteristics in this sort of case?

Yes; in that sort of situation, braking distance can be based on attainable speed.
 
Joined
9 Aug 2012
Messages
374
Location
Nottingham
On a vaguely related theme there are a couple of signals with flashing reds near Hucknall on the robin hood line. They seem to be associated with LCs shared with trams. Anyone here know what the flashing aspect means?
 

Bald Rick

Veteran Member
Joined
28 Sep 2010
Messages
17,864
On a vaguely related theme there are a couple of signals with flashing reds near Hucknall on the robin hood line. They seem to be associated with LCs shared with trams. Anyone here know what the flashing aspect means?

IIRC flashing reds on the approach to an ABCL or AOCL crossing mean the crossing equipment is active but not triggered. When the sequence is running it changes to flashing white.
 

D Foster

Member
Joined
5 Jan 2016
Messages
152
Location
N Staffs
Just a thought that'd been niggling away for a while - how's that work at, say, Woolmer Green Jn where a green on the Up Slow (3-aspect signal protecting the junction) can read to a single yellow (in a 4-aspect sequence if approached from the Up Fast), which would then give inadequate braking distance to the red if a train off the slow was able to accelerate to (nearly) linespeed before sighting the yellow? Is there an assumption made about the best possible acceleration characteristics in this sort of case?

I am not expert on this - but...

My impression is that you are suggesting that a train approaching the junction might get a green and then, instead of getting further greens through the junction, the route might be changed with the result that the next signal had become a single yellow on approach with a red beyond it protecting the junction.
Would that be a correct interpretation?

If so - it would seem to me to be the equivalent of an old style signalman allowing a train to approach with the Distant "Off" and then putting back in order to change the route through the junction. This was absolutely not allowed! If a change had to be made a train on clear signals had to be allowed to run clear or brought to a dead stand before the junction route was unlocked.
I would expect that something very similar would apply with all colour light/TCB signalling. The interlocking would, I think, prevent a green onto single yellow - or at least, it would hold the route in a similar way to the above.
Put another way - a train passing a signal at green shouldn't get a single yellow next - except with an emergency or fault put-back...

Am I basically correct about the interlocking please?

Thanks

:D
 

MichaelAMW

Member
Joined
18 Jun 2010
Messages
945
I am not expert on this - but...

My impression is that you are suggesting that a train approaching the junction might get a green and then, instead of getting further greens through the junction, the route might be changed with the result that the next signal had become a single yellow on approach with a red beyond it protecting the junction.
Would that be a correct interpretation?

If so - it would seem to me to be the equivalent of an old style signalman allowing a train to approach with the Distant "Off" and then putting back in order to change the route through the junction. This was absolutely not allowed! If a change had to be made a train on clear signals had to be allowed to run clear or brought to a dead stand before the junction route was unlocked.
I would expect that something very similar would apply with all colour light/TCB signalling. The interlocking would, I think, prevent a green onto single yellow - or at least, it would hold the route in a similar way to the above.
Put another way - a train passing a signal at green shouldn't get a single yellow next - except with an emergency or fault put-back...

Am I basically correct about the interlocking please?

Thanks

:D

He's not saying that. He's saying that there are situations where a slow line with 3-aspect signals converges with a fast line with 4-aspect signals. The aspect sequence is correst for both lines: a single yellow would be preceded by a green in 3 aspect but a double yellow in 4 aspect. The slower train would still have adequate braking distance from the single yellow.
 

bramling

Veteran Member
Joined
5 Mar 2012
Messages
12,197
Location
Hertfordshire / Teesdale
Just a thought that'd been niggling away for a while - how's that work at, say, Woolmer Green Jn where a green on the Up Slow (3-aspect signal protecting the junction) can read to a single yellow (in a 4-aspect sequence if approached from the Up Fast), which would then give inadequate braking distance to the red if a train off the slow was able to accelerate to (nearly) linespeed before sighting the yellow? Is there an assumption made about the best possible acceleration characteristics in this sort of case?

Before making any comments, please can I add the caveat that I don't sign this particular location - however I do travel over it regularly and have been party to some comments by drivers known to me that do sign it.

On the down, both the Down Fast and Down Slow have 4-aspect signals approaching Digswell Junction. I believe there is also a special control arrangement to as far as possible prevent a train being brought to a stand at the next signal due to the presence of the viaduct (can anyone confirm or add more about this?). In over 30 years travelling over this line I've never been on a train which has been brought to a stand at that signal.

On the up, the Up Slow signal approaching Woolmer Green Junction has a 3-aspect signal, with the Up Fast having a 4-aspect signal. I've heard it said that the braking distance is quite tight should a train come off the Down Slow on a green and then get a single yellow at the next signal (bear in mind modern EMUs will be probably be in the region of 80 mph when the next signal is sighted if they act upon the green aspect, but obviously route knowledge comes into play). Certainly experience as a passenger bears this out - I've experienced some pretty heavy braking when this scenario has occurred.

Hopefully others may be able to expand on some of this, as I've always found the inconsistent setup here mildly intriguing.
 

CyrusWuff

Established Member
Joined
20 May 2013
Messages
2,585
Returning to the topic of flashing greens, it's worth noting that they're still mentioned in Module LN2 of the London North Eastern Sectional Appendix, as follows:

Sectional Appendix said:
LN101 - KINGS CROSS TO SHAFTHOLME JN
New England North To Stoke Tunnel

Flashing green signal aspects for special test runs

In connection with special test runs the following arrangements will apply :-

1. Use of Flashing Green Main Signal Aspects

1.1 Flashing Green aspects (in addition to steady green aspects) have been provided on the:-
a) Down Fast line between Signal P487 (north of New England North) and P6l5 (approaching Stoke).
b) Up Fast line between Signal P610 (South of Stoke) and Signal P494 (south of Werrington Jn).

The meaning of a flashing green aspect is next signal exhibiting a steady or flashing green aspect.

The AWS will give a bell for both flashing and steady green aspects.

1.2 Drivers of all trains except test trains which are authorised to exceed 125 m.p.h., must treat flashing green aspects the same as steady green aspects.

1.3 Drivers of test trains authorised to exceed 125 m.p.h., must treat:-
a) a flashing green aspect as authority to exceed 125 m.p.h.
b) a steady green aspect as authority to proceed at or a requirement to reduce speed to 125 m.p.h.

2. Staff Safety

A special notice to staff will be issued when trains are authorised to exceed 125 m.p.h.

Dated: 02/12/06
 

Joseph_Locke

Established Member
Joined
14 Apr 2012
Messages
1,878
Location
Within earshot of trains passing the one and half
From what I gathered from Philip Phlopp the 225 sets can stop from 140mph from a double yellow comfortably, the issue is passenger comfort as it would be severe braking. I doubt Pendolinos would be any different in that regard.

A Pendolino can attain a brake rate of 12% of g, so 140mph to rest in 1800m.

GK/RT0075 Appendix C requires 2054m on a level gradient from 125mph so the Pendo stops safely* within the braking distance allowed.

* whether your cup of coffee survives is another question.
 

rebmcr

Established Member
Joined
15 Nov 2011
Messages
3,417
Location
Cambridge
1.3 Drivers of test trains authorised to exceed 125 m.p.h., must treat:-
a) a flashing green aspect as authority to exceed 125 m.p.h.
b) a steady green aspect as authority to proceed at or a requirement to reduce speed to 125 m.p.h.

So to answer the OP's question that has been skirted around many times, a steady green sighted by a 140mph train is treated as a restrictive aspect?
 
Status
Not open for further replies.

Top