Unusual Signal Sequence

[Skoodle]

On the East London Line extension, there is an unusual signal sequence that no one I have asked has been able to explain properly.

At Queen's Road Peckham station heading back towards the East London Line, we are presented with a double yellow aspect. Beyond that is the signal protecting Old Kent Road junction (where we cross over on to the Up East London Line) with a No.4 junction indicator. This displays green. We can see both at the same time. YY>G. Is this something to do with going from four to three aspect signalling? I thought it may be but surely if that was the case, it would be the signal protecting the junction maybe showing a single yellow and not the one before it?

We've been told it's just a local signalling quirk but I am interested to know what that quirk is.

Unfortunately the TfL promotional video only shows the route in the opposite direction towards Clapham so I can't find any video or photo to show yet.

 

[MarkyT]

On the East London Line extension, there is an unusual signal sequence that no one I have asked has been able to explain properly. . . . We've been told it's just a local signalling quirk . . . .

It doesn't sound right!

There are 5 types of junction signalling used normally:

Method/Description

1 / An unrestricted aspect displayed at the junction signal with the
normal 3- or 4-aspect sequence displayed on the approach

2 / Flashing yellow cautionary aspect sequence with a free single
yellow at the junction signal

3 / Approach control from red at the junction signal with the normal 3- or 4-aspect sequence displayed on the approach

4 / A free single yellow at the junction signal with the normal 4-aspect sequence displayed on the approach

5 / A splitting distant cautionary aspect sequence with an unrestricted aspect displayed at the junction signal

These are from Section 5.2 (page 47) of the following document:

Railway Group Standard GK/RT0045
Issue Three Date December 2012
Lineside Signals, Indicators and Layout of Signals

http://www.rgsonline.co.uk/Railway_...ng/Railway Group Standards/GKRT0045 Iss 3.pdf

The YY>G+JI sequence you describe doesn't fit with any of these.

Section 4.1.5 of the same document (page 40) deals with 4 to 3 aspect transitions:

Once again there is no case for that sequence.

I can only suggest that the YY is a temporary restriction for some technical reason associated with commissioning the new signalling. It is safe in the sense that the aspect displayed is more restrictive than necessary, but I would think not good practise except for short term exigencies.

 

[pendolino]

I don't know what the answer is, but maybe you could contact the signaller to report it as an irregular sequence and see what answer you get? If you do, be sure to report back here!

(On a similar subject, assuming you've just signed that route, be aware that it's not uncommon to be wrong routed at Peckham Rye on the down South London - the position 4 route indicator takes you onto the up Atlantic, while main aspect only is for the down Portsmouth towards East Dulwich. I've been offered (but never taken!) a wrong route there more often than anywhere else, although not for a while now)

 

[KingBBoogaloo]

That reminds me of something similar at Aldwarke Junction between Rotherham and Swinton.

When approaching the junction from Rotherham Central, the signal protecting the junction never clears to a green even when the next signal, which you can see, is at green.

I'm told the reason why is to remind Drivers about the drop in line speed from 55mph to 25mph across the junction.

No idea if its true though.

 

[Rich McLean]

That reminds me of something similar at Aldwarke Junction between Rotherham and Swinton.

When approaching the junction from Rotherham Central, the signal protecting the junction never clears to a green even when the next signal, which you can see, is at green.

I'm told the reason why is to remind Drivers about the drop in line speed from 55mph to 25mph across the junction.

No idea if its true though.

It may be that reason you said, if there is a drop in line speed for a crossover, and no AWS Block warning of the speed restriction, sometimes having the aspect as a YY on the approach is intended to alert drivers of a speed restriction ahead on the crossover.

However, it could also act as a reminder to slow the train down, as is always the chance, the driver is given the wrong road, and by slowing the train down, the driver has enough time to stop before the protecting signal, so that the signalman can change the road.

I'm sure a signalman can explain it better than I can

 

[moggie]

Doesn't fit with any standard aspect sequence so if there's been no briefing i'd report it as an irregularity albeit right side and see if an explanation is forthcoming. Just to confirm, I take it you see the green on the next but one signal beyond while approaching the preceding YY (not knowing the area you describe)?

 

[southerner2174]

I got told it was something to do with the interlocking mechanism, at least thats what it says on the route brief

 

[Skoodle]

Thanks for your replies gents. I'm leaning more to interlocking than to any other operational reason. I did forget to mention in original post, which would have helped a lot is that each time I've gone over, the signal protecting Old Kent Road Junction is at danger, with the single yellow at the end of the platform at Queens Road Peckham. Then after a short while it clears to give the sequence described.

There is a reduction in speed from 60 to 40, but the single yellow at the end of the platform takes care of that.

Pendolino, thanks for the head's up. I'll be taking it very cautiously for the first few months that's for sure!

 

[The Planner]

It does sound like an element of speed control. I bet it is a substandard braking distance in the signal sections and the YY aspect brings it in line.

 

[TDK]

Is there a TSR or ESR at the signal as I have known a signal to be keyed at 2Y before so the AWS always gives a caution!

 

[moggie]

I think this may explain it.

It's a bit technical but will no doubt explain the rationale to those ITK.

http://www.rgsonline.co.uk/Deviations/Derogation/11-038-DGN.pdf

 

[pendolino]

I think this may explain it.

It's a bit technical but will no doubt explain the rationale to those ITK.

http://www.rgsonline.co.uk/Deviations/Derogation/11-038-DGN.pdf

That's very interesting! Although this bit is a touch confusing:

Since trains using the divergence normally stop in the station and trains on the straight route do not

Have they forgotten about West Croydon <-> London Bridge services, which take the 'straight route' up to South Bermondsey but stop at Queens Road Peckham?

 

[Skoodle]

Bingo! Good find Moggie. Pendolino, I think they forgot about Southern

 

[MarkyT]

I think this may explain it.

It's a bit technical but will no doubt explain the rationale to those ITK.

http://www.rgsonline.co.uk/Deviations/Derogation/11-038-DGN.pdf

Very informative thank you, but the behaviour observed by the OP doesn't agree entirely with the description of the hybrid method in this derogation certificate: For a diverging train stopping at Queens Road, the junction signal is supposed to switch from 'MAR' to 'MAY' after the train has occupied the platform track circuit for a set time. That means the junction signal should change from red to yellow+junction indicator and the distant (which is also the platform starter) from yellow to double yellow. Standard 'MAY' arrangements call for the junction signal to not clear up to green until the train approaches the junction (assuming the next signal on the branch not stuck at red for whatever reason), or at least has passed the distant. Thus the normal sequence of aspects is maintained, not the double yellow reading to a green that was observed.