'Wrong' line signals south of Kennington Junction

[Nicholas43]

Please could forum member(s) explain why the signals before Kennington Junction on the 'wrong' line show puzzling (to me) yellows? Signal 2343, immediately before the junction, is reassuringly always red. But signal 2337 always shows yellow, and signal 2331 double yellow - even when there's a train approaching under green signals in the 'right' direction. To the uninitiated it looks as though I could turn up at the Sandford Lane access point with a trolley or something, see 2331 double yellow, and head off towards Oxford on the 'wrong' line.
Indeed, except in the (very rare?) circumstances when there is 'wrong' line working Didcot to Oxford, why do these signals need to show anything at all? Isn't it a waste of electricity and LED lifetime?

 

[Scottychoo]

You can't turn signals off! And as for just turning up with a trolley?!

 

[vinnym70]

It's something that's always puzzled me too - why not just red all the time? GEML exhibits the same on bi-directional sections so I assume it's standard.

 

[Tomnick]

The only thing that matters really is that nothing can be signalled onto that portion of line from one end whilst it’s occupied (or about to be) by something in the other direction. Once you’ve established that, then it doesn’t really matter what those signals are doing until something’s signalled towards them, and it’s quite a common arrangement. There’s little justification for the additional controls that’d be required to get them to behave differently.

You can't turn signals off! And as for just turning up with a trolley?!

To be fair, you can - there aren’t many approach lit signals about, but there are a few!

 

[Ianno87]

You can't turn signals off! And as for just turning up with a trolley?!

Yes you can. Scotland has loads of examples of signals unlit when not required (usually where they are on a loop without a corresponding signal on the main line)

 

[najaB]

To be fair, you can - there aren’t many approach lit signals about, but there are a few!

Scotland has loads of examples of signals unlit when not required (usually where they are on a loop without a corresponding signal on the main line)

I think most of the exit signals on the HML loops are only lit when there's a train in the loop, for example.

 

[pdeaves]

I haven't looked up the appropriate plan so may not be correct, but the double yellow and single yellow in the original post are probably the most restrictive aspects available. Those signals may not even have a red aspect to show if they are distant signals.

 

[Nicholas43]

Those signals may not even have a red aspect to show if they are distant signals.

That would surprise me. They look exactly the same as all the other new signals between Oxford and Didcot: two 'lights' (don't know the technical term) made up of lots of LEDs, top one can show red or yellow, bottom one can show green or yellow. [Oops, sorry, see correction in post #12]

 

[najaB]

I haven't looked up the appropriate plan so may not be correct, but the double yellow and single yellow in the original post are probably the most restrictive aspects available. Those signals may not even have a red aspect to show if they are distant signals.

Surely they would just be showing the appropriate sequence: red at the start of the bi-directional section, followed by yellow and double-yellow, no?

 

[Tomnick]

That would surprise me. They look exactly the same as all the other new signals between Oxford and Didcot: two 'lights' (don't know the technical term) made up of lots of LEDs, top one can show red or yellow, bottom one can show green or yellow.

A three aspect distant signal (Y/YY/G) would look exactly the same, though. It might even be the case that the signal head itself might be capable of displaying a red aspect, but if the interlocking never requires it, it’s still said to be incapable of showing a red aspect.

 

[Nicholas43]

Didcot - Oxford is supposed to be signalled for (exceptional?) bidirectional working, and there are stop signs on the 'wrong' platforms at Radley etc. If you were running a flight of trains wrong line Didcot to Oxford, mightn't you want them to form an orderly queue south of Kennington Junction?

 

[midland1]

The Red is always at the bottom unless it is a ground mounted signal. It is closer to the driver eye level and there is no hood below it for snow or the an upper hood to fall on it and block the Red signal.

 

[Tomnick]

Didcot - Oxford is supposed to be signalled for (exceptional?) bidirectional working, and there are stop signs on the 'wrong' platforms at Radley etc. If you were running a flight of trains wrong line Didcot to Oxford, mightn't you want them to form an orderly queue south of Kennington Junction?

Depends how much you're prepared to spend on it, I suppose. There aren't any intermediate stop signals, as far as I'm aware, so no 'flighting'. If these two signals were capable of showing a red aspect, to allow a second train to come from Didcot whilst the first is still standing at Kennington Junction, then you'd need distant signals in rear of those instead. In the grand scheme of things, it's presumably not justified by the benefit of being able to run a slightly less disrupted service on the odd occasion that something expires there!

 

[Nicholas43]

There's a surprisingly long berth between signal 2283 (south of Appleford) and 2331. But to my amateur eyes, it looks as though you could run, if not a flight, at least a worthwhile clump of trains wrong line Didcot to Oxford.