Signals Flashing?

[danfitz123]

Hi, just a simple question really but i would really like to know what it means when a yellow or double yellow signal is flashing. I see this all the time at acton bridge but have never known what it means.

 

[YorkshireBear]

Hi, just a simple question really but i would really like to know what it means when a yellow or double yellow signal is flashing. I see this all the time at acton bridge but have never known what it means.

as far as i know it is to do with an upcoming junction, i dont know if it has a proper term, but if your turning out so not sticking to main line it flashes.... i think there in use for rotheram central loop if i am right?

 

[starrymarkb]

Advance warning of a diverging route to be taken at speed.

 

[Ibex]

Double Flashing Yellow

The next signal is showing single flashing yellow.

Single Flashing Yellow

The next signal is showing single yellow with Junction indicator activated.

Diagram taken from here.

 

[Nym]

http://www.railsigns.co.uk/sect2page7/sect2page7.html

With the introduction of the Class 253 & 254 'High Speed Trains' (or 'InterCity 125s') to British Rail, it was found necessary to introduce two additional signal aspects. The new flashing aspects were designed to give the driver advance warning that the junction signal ahead (see Section 6) is showing a 'proceed' aspect applicable to the diverging route. Where there is more than one diverging route, the flashing aspects only refer to the highest speed divergence(s). A flashing single yellow aspect [2.115] means "Preliminary Caution - Be prepared to find the next signal displaying one yellow light, with a route indication for the highest speed diverging route". Where provided, the flashing double yellow aspect [2.116] means "Proceed - Next signal displaying flashing single yellow" and is an indication of a diverging route ahead of the next but one signal. The new flashing aspects were introduced from 1978 on all regions except the Southern, initially.

 

[Mojo]

For further background discussion see

http://www.railforums.co.uk/showthread.php?t=2776

and

http://www.railforums.co.uk/showthread.php?t=26578

 

[Hydro]

It's a system known as approach control, and indicates to the driver the route ahead has been set for a diverging route that has a lower speed than the through route so the driver can adjust speed accordingly.

 

[danfitz123]

Thanks for the replies everyone and thanks for the diagram james. You've solved one of many many questions in life .

 

[O L Leigh]

Diagram taken from here.

...and it's incorrect.

The junction signal would only be held at single yellow if the first signal on the diverging route was a red. In practice it could be showing any proceed aspect depending on what the next signal is, though until a driver gets sight of the junction signal they must always assume that it is at the most restrictive aspect (single yellow).

O L Leigh

 

[moggie]

err no it's not. The junction protecting signal will only clear up from yellow to better aspect depending on the aspect displayed beyond the junction AFTER the train has passed the flashing single yellow signal.

Furthermore, the flashing sequence is inhibited if the train is within minimum reading distance of the signal that would display a flashing yellow OR if the signal intended to display a flashing single yellow suffers an equipment failure preventing flashing of the aspect. In either situation the junction signal will be held at red with standard approach release from red applied. Signals on the approach then adopt a standard 3 or 4 aspect sequence.

The above is enforced by interlocking.

GK/RT0045 refers.
--- old post above --- --- new post below ---
And England are 1- 0 up in the test v the Aussies!!!!

Bring it on!

 

[Aictos]

On the ECML, this is in operation at Woolmer Green at the Stevenage end of Welwyn viaduct as you head north which lets you know if you're being signalled onto the Down Slow or continue on the Down Fast.

It is also in operation south of Hitchin on the Down Fast as it lets you know that you're being signalled onto the Down Slow to serve Hitchin useful when you're a EC working and you need to stop in the Down Platform for whatever reason.

I can't think where else it's in operation in my area though?

 

[Tomnick]

Also coming off Digswell Viaduct in the Up direction, towards the Up Slow?

 

[Zoe]

One curiosity is Westerleigh Junction. The diverging speed is 30 mph with the main line speed at 100 mph. I thought flashing yellows were only used where the divergence was higher in speed. There is a 70 mph difference here.

 

[Hydro]

It's for when the turnout speed is significantly less than the through speed I believe. The 70mph difference at Westerleigh would
necessitate flashing yellows.

 

[Zoe]

It's for when the turnout speed is significantly less than the through speed I believe. The 70mph difference at Westerleigh would
necessitate flashing yellows.

I would have thought such a large difference would warrent approach control but maybe not.

 

[Aictos]

Also coming off Digswell Viaduct in the Up direction, towards the Up Slow?

Not sure, sorry

 

[Tomnick]

I would have thought such a large difference would warrent approach control but maybe not.

If I'm not mistaken, flashing yellows were initially intended for junctions with a relatively small difference in speed between the straight route and highest speed diverging route (but not so small that no approach control was required!). Clearly it'd be not very clever to provide a high-speed-ish divergence and then provide signalling that brings everything right down on the approach anyway.

However, the benefits would extend to lower-speed divergences too, as the Driver still only has to brake for the speed at the junction (with consideration for the next signal of course, which probably wouldn't come into the equation at a low-speed junction anyway) rather than preparing to come to a stand at the junction signal, some 200yds or more in rear. It's never going to be installed everywhere of course (compliance with standards would make that impossible anyway), but it still seems an effective way of increasing capacity at key junctions.

 

[hello]

40 over westerleigh

 

[BR 1979]

It's for when the turnout speed is significantly less than the through speed I believe. The 70mph difference at Westerleigh would
necessitate flashing yellows.

less than 50% of line Speed if my memory serves me correctly .
They were brought in to relay the information to the driver that he was approaching a Junction and that the points were set for the diverging route. Before flashing yellows it was just a case of bringing the train speed down with restrictive aspects and a timer on the approach track to the Controlling Signal before the junction. The problem this caused was that the driver never knew if he was being brought to a stand at the signal or if his speed was being controlled for the diverging junction and that the points were set and the controlling signal was about to clear. Drivers became too familiar with certain junctions and many passed signals (SPADs) expecting the signal to clear. Conversely with freight trains having to slow right down for an expected stop at the controlling signal it was very time consuming (and fuel consuming) for them to accelerate once they had slowed expecting to stop, and then the signal had cleared for the diverging route..
With the 'flashers' I installed in early 80's ,the Junction Approach Locking would have a timer on the approach track (long 4 section track circuits) to ensure the train speed has decreased appropriately when approaching the Junction Signal. If it had the Junction Signal would then normally clear from single yellow to Green providing relevant signals on the diverging route where showing a proceed aspect (minimum double yellow on a four aspect block) This was so he did not need to continue braking as he passed the Junction Controlling Signal as the diverging route was 'clear ahead' . Otherwise if the Junction Controlling Signal was maintained at Single Yellow the Driver would still expect the next signal on the diverging Route to be at Danger (Red) and continue to slow.

 

[Zoe]

40 over westerleigh

Since when? My sectional appendix shows the diverging speed from the Up Badminton (SWB) to Up Charfield (YAT) as 30 mph.

 

[The Planner]

Been like it for about a year, the junction has a 30 Freight 40 Passenger diff. on it.

 

[Zoe]

Been like it for about a year, the junction has a 30 Freight 40 Passenger diff. on it.

Oh right, it seems the down Charfield to Down Badminton was 30/40 some time before this though.

 

[ralphchadkirk]

I take it you were using the Baseline declaration then, rather than the actual sectional appendix?

 

[Zoe]

I take it you were using the Baseline declaration then, rather than the actual sectional appendix?

No, a real sectional appendix although not the most recent. In 2006 it was shown as 30 Up Badminton to Up Charfield and 30/40 Down Charfield to Down Badminton. I'd be interested to know what enabled the speed to be rasied.

 

[hello]

40 over the p and c then 55

 

[furryfeet]

Not so !

The junction signal could be at red, if the diverging route was blocked via a conflicting movement.
The driver must never assume that the route beyound the junction is clear and be prepared to slow down or even stop at the junction signal.
This was the fundamental mistake made by the driver of the Manchester train in the 1986 Colwich crash - the flashing yellow diverging route had been set by the signalman, but the junction signal was still at red since there was a train coming from Liverpool at the same time. Consequently the Manchester train overran the junction signal and collided with the oncoming Liverpool train.

 

[ralphchadkirk]

As an old-hand driver once told me; there is no such thing as an approach controlled signal.

 

[Zoe]

Not quite, the situation at Colwich was that the first junction signal (down fast to down slow) was a single steady yellow. The driver wrongly assumed that having seen the flashing yellows this would mean the line was clear all the way through the junction and did not expect to see the next signal (down slow to down stoke) at red. The sequence was NOT 2 flashing yellows, 1 flashing yellow, red.

 

[YorkshireBear]

Not so !

The junction signal could be at red, if the diverging route was blocked via a conflicting movement.
The driver must never assume that the route beyound the junction is clear and be prepared to slow down or even stop at the junction signal.
This was the fundamental mistake made by the driver of the Manchester train in the 1986 Colwich crash - the flashing yellow diverging route had been set by the signalman, but the junction signal was still at red since there was a train coming from Liverpool at the same time. Consequently the Manchester train overran the junction signal and collided with the oncoming Liverpool train.

just read up on the colwich crash.... off topic but i cannot believe only 1 person died in that, seeing pictures of wreckage i cant believe that...

 

[pendolino]

The driver wrongly assumed that having seen the flashing yellows this would mean the line was clear all the way through the junction and did not expect to see the next signal (down slow to down stoke) at red.

Apparently he didn't understand the signal sequence. So says the wikipedia page on Colwich anyway:

The Inspector's report recommended changing the signalling sequence so that flashing yellows would only be used when the line was clear throughout the whole junction, as the driver was expecting.

I wonder whether there are drivers who still don't quite fully understand that there can be a red after the single yellow after the flashing yellows. On my rules course, it was one topic that took a few people a while to fully comprehend. (I have also had a conductor call me to ask whether flashing yellows on a starter signal is a proceed aspect so he could give 2 bells. It made me chuckle at the time, but then I don't know if conductors are taught signalling in such depth to be fair).

just read up on the colwich crash.... off topic but i cannot believe only 1 person died in that, seeing pictures of wreckage i cant believe that...

Absolutely. Quite astonishing that there was only one fatality.