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| 4 aspects to 2 aspects - exist? 25/08/2013 at 23:34 #48844 | |
arabianights
138 posts |
Is there anywhere with a 4 aspect signal followed afterwards by two 2 aspect signals. And if there is, what does the 4 aspect signal show if the 2nd of the 2 2 aspect signals is danger - two yellows because the 2nd signal is red, or green because two yellows means expect a yellow signal (which is never going to appear). And even if it doesn't exist, which of the above interpretations is correct for how it would be signalled? Log in to reply |
| 4 aspects to 2 aspects - exist? 25/08/2013 at 23:43 #48845 | |
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Late Turn
699 posts |
You couldn't have two successive 2-aspect stop signals (leaving aside the Merseyrail and LUL examples) as that'd potentially give you a green reading onto a red - which isn't a good thing (how are you expected to know about the red in time to stop at it?). The closest you'll find is a colour-light signal stop signal reading to, and acting as the distant for, two or more semaphore stop signals (which would all need to be cleared to permit the CL signal to clear to green) - and even then it'd only be a 4-aspect signal if the YY was required for other routes from it.
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| 4 aspects to 2 aspects - exist? 25/08/2013 at 23:49 #48846 | |
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vontrapp
210 posts |
Yes, there is. It is a green signal leading to a 'cleared' ground position signal. I do not know about the rest of your question and I would visit the SB, that has this situation, to clear-up the question, unless someone else wants to contribute. Last edited: 25/08/2013 at 23:54 by vontrapp Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 02:52 #48849 | |
GeoffM
6376 posts |
Well, a 4-aspect followed by R/G 2-aspect and then another R/G 2-aspect is theoretically possible - but the line speed between the two latter would have to be extremely low - 10mph or less IIRC. The 4-aspect would display Y in that case of the middle signal showing R (regardless of the 3rd signal), and G if G. As to whether there are any examples left on the main line... I don't know. 4-aspect followed by Y/G followed by R/G is also possible, but probably only if the 4-aspect was a junction signal and thus applying more to the main line than the 2-aspect branch. The 4-aspect would display G reading to the Y/G regardless of the aspect shown by the Y/G. Note that there are probably cases of showing YY if the Y/G is showing Y. SimSig Boss Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 07:22 #48850 | |
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Late Turn
699 posts |
Geoff, the arrangement on the Down at Holmes Jn (Sheffield sim) almost sounds like what you describe - 4-aspect signal on the main line reads to a 2-aspect repeater (Y/G) on Holmes chord, followed by a 3-aspect stop signal (which could just as well be a 2-aspect signal as far as this discussion is concerned). In that case, the first signal clears to YY if the repeater's at Y - although I agree that G is likely in other cases with much greater signal spacing. " said: Yes, there is. A main aspect can't read to a position light signal - although you might find a 'running' shunt within a route, it won't affect the aspect sequence on the main aspects in rear. I can't see any relevance to the original question? Last edited: 26/08/2013 at 07:23 by Late Turn Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 07:45 #48852 | |
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Forest Pines
525 posts |
There are more examples in the Edinburgh area - off the top of my head, the Bathgate branch used 2-aspect signalling off a 4-aspect main line. I don't know if the signalling's been upgraded as part of the Airdrie reopening. In general I suspect the aspect shown by the 4-aspect signal would depend on the distance to the next signal. I think the Holmes example above shows 2 yellows if the next stop signal is red, but the Newbridge Jn example shows green. Last edited: 26/08/2013 at 07:46 by Forest Pines Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 11:38 #48855 | |
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Zoe
252 posts |
" said:You couldn't have two successive 2-aspect stop signals (leaving aside the Merseyrail and LUL examples) as that'd potentially give you a green reading onto a red - which isn't a good thing (how are you expected to know about the red in time to stop at it?). I know this is very unlikely but couldn't there be a situation where two aspect colour lights have been used as replacements of semaphores rather than MAS? This system was used by the GWR in the 1930s colour light schemes using two aspect searchlight signals. Due to the distances betwee the boxes though, I believe most of these signals would have had two aspect searchlight distant below them though. Last edited: 26/08/2013 at 22:35 by Zoe Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 12:11 #48856 | |
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AndyG
1842 posts |
Two aspect signals are quite common on lower speed lines where semaphores have been updated, eg the West of England line from Salisbury to Exmouth Jn (also Worting Jn to Salisbury). Typically a Y/G repeater at the old distant location, with a R/G home signal, with a long distance to the Y/G (say 5 miles) followed by 3/4 mile to the R/G ie the repeater is the braking distance in rear of the home rather than evenly spaced. Long sections are acceptable due to a less intensive service and much longer headways with 1 or 2 tph rather than suburban services. An example of a 4 aspect signal leading into 2 aspect signalling could be at a diverging junction, with 4 aspects available on the main route, but the YY is inhibited with a route set into 3 or 2 aspect MAS. I can only help one person a day. Today's not your day. Tomorrow doesn't look too good either. Last edited: 26/08/2013 at 12:12 by AndyG Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 13:03 #48857 | |
Steamer
3984 posts |
" said:You couldn't have two successive 2-aspect stop signals (leaving aside the Merseyrail and LUL examples)Are you sure about Merseyrail? I thought that since it's part of Network Rail it would require yellow before red. "Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q) Log in to reply |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 13:54 #48859 | |
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Late Turn
699 posts |
I'm sure I've read somewhere that some of the signals on the Wirral Loop don't have repeaters - could be wrong though. Edit: This photo suggests that there are some signals on the Loop that don't have repeaters (note G to R on 516 to 514), whilst others have repeaters co-located with the stop signal in rear (as on LU lines). " said: " said:You couldn't have two successive 2-aspect stop signals (leaving aside the Merseyrail and LUL examples) as that'd potentially give you a green reading onto a red - which isn't a good thing (how are you expected to know about the red in time to stop at it?). That sort of situation might have arisen many years ago, but I can't think of a single example in recent years. Where a semaphore home signal has been replaced by a colour light (considering the 'typical' AB layout of distant, home, starter), its replacement has usually been a 3-aspect signal - either moved back to provide braking distance to the starter or with a delayed yellow (or at least distant maintained at Caution) otherwise - or the starter has been abolished altogether. Last edited: 26/08/2013 at 14:00 by Late Turn Log in to reply The following user said thank you: Steamer |
| 4 aspects to 2 aspects - exist? 26/08/2013 at 15:21 #48862 | |
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Stephen Fulcher
2078 posts |
" said:BS108, BS104R, BS104 between Kings Sutton and Aynho Junction is one such example, although four aspect BS108 cannot display a single yellow aspect. Log in to reply |
| 4 aspects to 2 aspects - exist? 27/08/2013 at 00:44 #48887 | |
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vontrapp
210 posts |
4 aspect to a 2 aspect.........., was the question.
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| 4 aspects to 2 aspects - exist? 27/08/2013 at 00:47 #48888 | |
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vontrapp
210 posts |
" said:Geoff, the arrangement on the Down at Holmes Jn (Sheffield sim) almost sounds like what you describe - 4-aspect signal on the main line reads to a 2-aspect repeater (Y/G) on Holmes chord, followed by a 3-aspect stop signal (which could just as well be a 2-aspect signal as far as this discussion is concerned). In that case, the first signal clears to YY if the repeater's at Y - although I agree that G is likely in other cases with much greater signal spacing.4 aspect to a 2 aspect.........., was the question. Log in to reply |
| 4 aspects to 2 aspects - exist? 27/08/2013 at 06:30 #48889 | |
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Forest Pines
525 posts |
" said:I think the wording of the question implied "running signals" was clearly meant - or "fixed running signals" if you want to go to extremes. Log in to reply |
| 4 aspects to 2 aspects - exist? 27/08/2013 at 09:57 #48892 | |
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kbarber
1742 posts |
" said:" said:" said:You couldn't have two successive 2-aspect stop signals (leaving aside the Merseyrail and LUL examples) as that'd potentially give you a green reading onto a red - which isn't a good thing (how are you expected to know about the red in time to stop at it?). My understanding is that if a semaphore home signal is replaced by a colour light, a 3-aspect signal is absolutely required. The delayed yellow if starter at danger is also a requirement - a yellow seen afar is considered potentially misleading, as a (momentarily disoriented?) driver could assume full braking distance from it to the signal at danger. The exception, as Tom says, is if full braking distance exists from home to starter. Which is not to say that other configurations didn't exist historically (although I can't think of any off-hand). Returning to the original question, there are a number of 4-aspect signals on the LUL fast lines north of Harrow on the Hill. I don't recall whether any of them act as junction signals to the slow lines (Watford Junction (south) and Harrow North Junction are the only possibilities if I recall the layout correctly) but in that case a 4-aspect signal would read to LUL-style 2-aspect signalling. Maybe not quite what the OP had in mind but I suppose technically it fits. Log in to reply |
| 4 aspects to 2 aspects - exist? 27/08/2013 at 11:00 #48893 | |
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Zoe
252 posts |
" said:Which is not to say that other configurations didn't exist historically (although I can't think of any off-hand). The 1930s GWR colour light schemes? Last edited: 27/08/2013 at 11:00 by Zoe Log in to reply |
| 4 aspects to 2 aspects - exist? 27/08/2013 at 18:05 #48908 | |
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kbarber
1742 posts |
" said:" said:Which is not to say that other configurations didn't exist historically (although I can't think of any off-hand). Sorry, should've said '...apart from...'. Certainly I'm not aware of any such installations on the LNER, LMS or SR - in every case I can think of a red was preceded by a yellow. GW practice, of course, was already a pretty gross anachronism. Log in to reply |
| 4 aspects to 2 aspects - exist? 01/09/2013 at 12:35 #49072 | |
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clive
2789 posts |
" said:Yes, those are the only two cases. At Watford South Junction there's a 3 (not 4) aspect signal JJ71 reading to a 2 aspect A793. I'd expect it to show yellow if A793 was red. At Harrow North Junction there's a 4 aspect JB45/46 reading to a Y/G repeater RJB68 and then a G/R/#4/G/Y stack JB68+RJB65/66 (the bottom three are a repeater for the junction signal in advance). That could read green with JB68 at red because of the repeater. Oops, there's a third case: at Chalfont and Latimer 3-aspect JT80 on the northbound line reads to 2-aspect JT83 on the branch. And a fourth: JW71 and JW72 (the two Amersham northbound starters) are 3-aspect and read to the 2-aspect JW70 just before Mantles Wood Junction (this then reads to Y/G ME375R). My reading of the LU rules is that 3- and 4-aspect signals are to be interpreted as such even if the next signal in line is 2-aspect. So they'd show yellow with a 2-aspect red next. Log in to reply |
| 4 aspects to 2 aspects - exist? 01/09/2013 at 12:39 #49073 | |
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clive
2789 posts |
" said:I'm sure I've read somewhere that some of the signals on the Wirral Loop don't have repeaters - could be wrong though.Isn't that because it's showing in panel signal mode, so 516 is actually yellow even though the screen shows green? The only yellow on there is a repeater. Hmm, on looking closer, it seems that there are co-located repeaters. Perhaps you're right, though it's unusual if so. Log in to reply |
| 4 aspects to 2 aspects - exist? 01/09/2013 at 13:46 #49075 | |
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TomOF
452 posts |
You are correct in saying that some of those signals don't have any yellow aspects to the next possible red. This is mitigated by the slow-ish speeds round the loop, the proximity of one station stop to another, the fact that practically all trains stop at every station and the rather robust train stop equipment. Where repeaters do exist they are mounted in the same place as the preceding signal. And if that wasn't unusual enough, the signal aspects where originally mounted side by side (not sure if they've been replaced by searchlights since)..
Last edited: 01/09/2013 at 13:48 by TomOF Log in to reply |
| 4 aspects to 2 aspects - exist? 27/09/2013 at 12:54 #49631 | |
beast66606
6 posts |
" said:" said:The underground sections have different rules, green onto red is permissable, the outside section conforms to the normal signalling standards.You couldn't have two successive 2-aspect stop signals (leaving aside the Merseyrail and LUL examples)Are you sure about Merseyrail? I thought that since it's part of Network Rail it would require yellow before red. Log in to reply |