Deleted
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Post by Deleted on Dec 10, 2007 23:35:10 GMT
....and then applying the correct procedure (LUL track in this instance), the driver must remain at speed at which he can stop short of obstruction until he passes 2 consec. stop sigs showing clear. Ok.
But what is the actual need for/reasoning behind having to pass TWO clear signals? Why not just 1?
Now, I know its something to do with overlaps, but what exactly?
There endeth my knowledge on this subject I'm afraid!
Ta.
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Deleted
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Post by Deleted on Dec 11, 2007 0:51:35 GMT
Because with ordinary overlaps (rather than absolute overlaps which we have in most places now) if the overlap is big it would be possible for there to be a green signal and a train ahead (if it was in the overlap). So therefore the blanket rule is 2 stop signals showing clear or caution before resuming normal line speed.
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Deleted
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Post by Deleted on Dec 11, 2007 2:06:29 GMT
Will the newer moving block systems and their (mostly) infinitely adjustable overlaps force a change in this rule at any point?
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Colin
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Post by Colin on Dec 11, 2007 3:35:37 GMT
Extremely likely I should think - but we won't know until it arrives and the training starts.........
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Post by Deleted on Dec 11, 2007 9:07:50 GMT
Oh, I see. Thanks tfc.
But I thought most signalling on LU used ordinary overlaps though??
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Post by Deleted on Dec 11, 2007 10:50:01 GMT
Well on the Central and Vic trains can resume coded manual working as soon as a code is picked up - so yes the rules are different with ATP.
Most signalling on LU now uses absolute overlaps I believe, someone might correct me as I'm not a signals expert though. I know on the north end of the Bakerloo (on the national rail section) there are some pretty big ordinary overlaps - I once had the interesting experience of my train becoming stalled just leaving North Wembley, having no radio contact and walking back to the signal which was just to the rear of my train to use the signal phone - it was green, despite the whole of my train being past the signal (and in the overlap, clearly).
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Post by Harsig on Dec 11, 2007 13:03:48 GMT
And of course short trains occasionally operate on LUL which may fit between the signal and the replacing track circuit block joint. I'm thinking here of things like Tamping Machines and I've seen single Battery Locos now and again (On one occasion going to rescue a failed tamping machine which was stalled entirely past a signal that was still clear.)
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Post by tubeprune on Dec 11, 2007 18:28:50 GMT
Well on the Central and Vic trains can resume coded manual working as soon as a code is picked up - so yes the rules are different with ATP. Most signalling on LU now uses absolute overlaps I believe, someone might correct me as I'm not a signals expert though. I know on the north end of the Bakerloo (on the national rail section) there are some pretty big ordinary overlaps - I once had the interesting experience of my train becoming stalled just leaving North Wembley, having no radio contact and walking back to the signal which was just to the rear of my train to use the signal phone - it was green, despite the whole of my train being past the signal (and in the overlap, clearly). The standard BR overlap was (and still is, I think) 183m. They didn't calculate them like LU does. |
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Tom
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Post by Tom on Dec 12, 2007 12:58:56 GMT
I believe they have now changed to 180m. However, now that TPWS is available there is more attention on where a train will stop after passing a TPWS fitted signal at danger - which is getting closer to calculating overlaps like LU do.
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mrfs42
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Post by mrfs42 on Dec 12, 2007 13:20:43 GMT
I believe they have now changed to 180m. That is true for new installations. There'll still be plenty of places where the old 440 yards still applies for a while yet. However, now that TPWS is available there is more attention on where a train will stop after passing a TPWS fitted signal at danger - which is getting closer to calculating overlaps like LU do. Yes, a lot more attention is now being paid to where the OSS and TSS beacons are placed and their position is calculated for arming purposes. |
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Deleted
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Post by Deleted on Jan 14, 2008 8:29:16 GMT
On the same subject, what is the wording of the sign on the M door on a C stock? (the one beginning "After passing a signal at Danger under rule...")
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Post by c5 on Jan 14, 2008 11:07:01 GMT
On the same subject, what is the wording of the sign on the M door on a C stock? (the one beginning "After passing a signal at Danger under rule...") Expect to find a train ahead. And then a reminder to to pass Semi-Automatic Signals at danger, without the correct authorisation. Here it is on COLIN's Photo site ;D www.districtlinephotos.co.uk/html/c_stock_gallery_8.html |
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Colin
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Post by Colin on Jan 14, 2008 18:45:33 GMT
And the D stock version: www.districtlinephotos.co.uk/html/d_stock_gallery_5.htmlThey're not the best images in the world, but they give the idea. All trains have something similar in the cab - unfortunately it is deemed necessary to remind us train ops of the rules. Note to self: I really must re-acquire the program for that website and get it updated   |
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