Deleted
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Post by Deleted on Jun 16, 2014 21:50:11 GMT
Tonight while I was changing from NLL to ELL at Canonbury, I noticed the signals on platform 3 (westbound NLL) acting in a way that seemed odd to me... Once the previous Willesden service had departed, the signal behind it (NL1254) naturally showed a red aspect, followed by yellow and double yellow in turn as the sections cleared. However there appeared to also be a signal at the eastern end of the platform (NL1249), seemingly controlling a possible eastbound departure. However, shortly before the approach of the next westbound train, this signal cleared first to yellow and then double yellow. This seems to go against the basic rules of signalling as I know them.  Can anyone explain what's going on here? |
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Post by Deleted on Jun 16, 2014 22:14:42 GMT
I thought the triangle indicated that this is a distant signal for signal NL 1249. What was this signal showing before it "cleared first to yellow and then double yellow". I didn't think distant signals could show danger?
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Post by Deleted on Jun 16, 2014 22:34:07 GMT
Oops, bad wording on my part. I can't claim to have seen it at red. Single and double yellow I CAN vouch for. I wasn't there long enough to see it change again.
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Post by Deleted on Jun 16, 2014 22:51:48 GMT
I suspect, in that case, it was merely doing its job as a distant signal for NL 1249. I have no knowledge of the signalling around this location and would likewise be very interested to hear more. If, though, there is bi-directional running on this section, as there seems to be, this seems to be quite normal. I've seen something similar on the C2C, I started writing a speculative paragraph but - you know what - it's probably better if I wait for someone who knows what they're talking about  |
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rincew1nd
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Post by rincew1nd on Jun 17, 2014 6:48:00 GMT
Whilst the picture may seem intuitively wrong at first, the white triangle on the number plate (a delta) indicates that this signal cannot show a red aspect.
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Post by Deleted on Jun 17, 2014 7:53:18 GMT
It's a fairly common arrangement for the signalling in the "non-normal" direction of a bi-directional line and it is working correctly.
The stop signal ahead is a controlled signal and thus normally displays a red aspect. It is provided with two repeaters and the picture shows the "outer" of the two. With no train between the stop signal and the "outer" repeater and the stop signal at danger then the repeater will display two yellows.
What the op observed initially was the "outer" repeater displaying one yellow meaning a train was present between it and its stop signal. When that train cleared the track circuit block joint/axle counter head a short distance in advance of the "outer" repeater then as far as the interlocking is concerned there is no train between the repeater and its stop signal and so the repeater stepped up to two yellows.
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Post by Deleted on Jun 17, 2014 11:11:41 GMT
Fascinating! Thank you so much for explaining this.
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Post by roboverground on Jun 18, 2014 9:24:36 GMT
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Post by Deleted on Jun 18, 2014 13:23:58 GMT
"R" is used for a single repeater or the inner repeater of two. "RR" is the suffix for the outer repeater of two so if a suffix had been used on the signal shown then it would be "RR" |
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Post by Deleted on Jun 22, 2014 15:08:17 GMT
From my signalling diagram NL1249 protects a fixed red aspect at NL1258 (limit of bi-directional shunt), located between BR141 Mildmay Park and BR142 King Henry's Walk.
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