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| Signaling Puzzle 14/09/2016 at 15:45 #84829 | |
Jersey_Mike
250 posts |
Below is a link to a photo that caused a lot of puzzlement amoung American railfans and I wanted to see if anyone here would be able to figure out what was going on. I'll ask any North American signal fans who know the answer to please let the Europeans and British first crack at answering. Regarding the picture, it is not a result of trick photography or any sort of signaling malfunction. The layout is one end of a passing siding on a single track line where the two tracks merge through a single switch. There are no other possible routes that simply aren't visible in the photo. http://www.railpictures.net/images/d2/4/7/1/5471.1473067586.jpg The answer should include a brief explanation about this situation is not actually dangerous. Let me know if you need a hint. Last edited: 14/09/2016 at 15:46 by Jersey_Mike Log in to reply |
| Signaling Puzzle 14/09/2016 at 15:59 #84831 | |
kaiwhara
587 posts |
Signal Testing under line closure conditions?
Sorry guys, I am in the business of making people wait! Log in to reply |
| Signaling Puzzle 14/09/2016 at 16:02 #84832 | |
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Jersey_Mike
250 posts |
" said:Signal Testing under line closure conditions?Nope, the line is in service and the signal is in fact being lit by an approaching train. Log in to reply |
| Signaling Puzzle 14/09/2016 at 16:06 #84834 | |
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Ron_J
331 posts |
Long exposure.
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| Signaling Puzzle 14/09/2016 at 16:12 #84835 | |
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Jersey_Mike
250 posts |
" said:Long exposure.Like I said no photographic tricks or editing was used. A long exposure would count as a trick and also in this case you'd see extra red lamps lit up it someone tried a straight timed shot. You might be able to fake the effect with a double exposure, but I've seen other pictures of this signal in the daytime so I know its legit. Log in to reply |
| Signaling Puzzle 14/09/2016 at 16:21 #84836 | |
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Finger
220 posts |
Are there spring loaded points, or is it some similar situation where the interlocking doesn't really control or indicate which train (from which track) actually has the permission to run?
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| Signaling Puzzle 14/09/2016 at 16:42 #84838 | |
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JamesN
1607 posts |
2 signals are shown, each with two heads. The searchlight-style head (displaying red in both cases) has the meaning stop, and controls entry into the block section ahead. The green indications will be some form of speed indication, it isn't "unsafe" (by US standards) as it is accompanied by a Red stop indication. Exactly what the meaning of the speed indication is I'm afraid I don't know, possibly "medium"... ??? Log in to reply |
| Signaling Puzzle 14/09/2016 at 17:42 #84843 | |
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Jersey_Mike
250 posts |
" said:2 signals are shown, each with two heads. The searchlight-style head (displaying red in both cases) has the meaning stop, and controls entry into the block section ahead.I guess I should have explained that the left signal is displaying G/R "Clear" for the main track and the right signal is displaying R/G "Diverging Clear" for the siding. Both routes proceed over the same trailing point switch but... " said: Are there spring loaded points, or is it some similar situation where the interlocking doesn't really control or indicate which train (from which track) actually has the permission to run?Yes...there is indeed a trailing point spring switch, which is good for half credit. Both routes are valid in terms of not being in conflict with an improperly lined switch. Can anyone else identify the larger context where both the siding and the main track can present proceed indications at the same time? I'll give you all a big hint. What is pictured is not actually an interlocking. 
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| Signaling Puzzle 14/09/2016 at 21:14 #84847 | |
Dick
387 posts |
Its in the USA, they do what they like with the railways over there.  I've just come back from the States where I stayed in a hotel in Rapid City overlooking a level crossing on a very busy main road. Interesting to say the least!!
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| Signaling Puzzle 14/09/2016 at 22:34 #84848 | |
BarryM
2158 posts |
Which Railroad controls this location? Barry Barry, Sydney, New South Wales, Australia Log in to reply |
| Signaling Puzzle 14/09/2016 at 22:48 #84849 | |
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BarryM
2158 posts |
" said:Below is a link to a photo that caused a lot of puzzlement amoung American railfans and I wanted to see if anyone here would be able to figure out what was going on. I'll ask any North American signal fans who know the answer to please let the Europeans and British first crack at answering. Regarding the picture, it is not a result of trick photography or any sort of signaling malfunction. The layout is one end of a passing siding on a single track line where the two tracks merge through a single switch. There are no other possible routes that simply aren't visible in the photo.There are 3 tracks in this photo. The left hand signal controls the furthest most track. The right hand signal controls the Right hand line ahead of the switch. Barry Barry, Sydney, New South Wales, Australia Log in to reply |
| Signaling Puzzle 15/09/2016 at 01:21 #84851 | |
GeoffM
6376 posts |
" said:There are 3 tracks in this photo. The left hand signal controls the furthest most track. The right hand signal controls the Right hand line ahead of the switch.The three tracks merge into two, there are two signals for the two remaining tracks, and then the two tracks merge into one. Both signals are showing proceed aspects onto the single line which ought not to be possible. Mike is saying that in this instance it's safe... but why? Not quite the same but SP apparently used to have a rule where a driver could set the points to exit a loop ("siding" which put the main line signal to danger, and then wait 4(?) minutes. If nothing came screeching to a halt in that 4 minutes then they were good to go. Probably other rules involved too.
SimSig Boss Log in to reply |
| Signaling Puzzle 15/09/2016 at 07:17 #84855 | |
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Dick
387 posts |
Is it because once the 3 tracks have merged to 2, there will only ever be a train on one or other of those tracks but due to lack of track circuiting it is not known which. Therefore proceed is displayed on both.
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| Signaling Puzzle 15/09/2016 at 12:57 #84892 | |
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Jersey_Mike
250 posts |
BarryM said:Which Railroad controls this location?Norfolk Southern. That's actually the big reason even locals were confused. This sort of setup is more typically encountered out west. Dick said: Is it because once the 3 tracks have merged to 2, there will only ever be a train on one or other of those tracks but due to lack of track circuiting it is not known which. Therefore proceed is displayed on both.The presence of the industrial track switch doesn't really factor in to the puzzle. Situations do exist however where multiple yard or siding tracks converging over hand operated points can be governed by one signal. Log in to reply |
| Signaling Puzzle 16/09/2016 at 06:11 #84949 | |
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Hawk777
386 posts |
Jersey_Mike said:Yes...there is indeed a trailing point spring switch, which is good for half credit. Both routes are valid in terms of not being in conflict with an improperly lined switch.Are these part of a bidirectional automatic block signalling system, in which permission to exit the siding or to traverse the track in a particular direction must be obtained by e.g. track warrant and the signals are only used to separate following trains in the same direction, these being automatic signals which are both indicating that the track ahead is clear? Although I’m not sure why trailing points would be protected by a diverging clear indication (they’re not diverging…) Log in to reply The following user said thank you: Jersey_Mike |
| Signaling Puzzle 16/09/2016 at 11:21 #84974 | |
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Jersey_Mike
250 posts |
Hawk777 said:Yay! Someone got it! I'd give you an emoji, but they seem to have vanished. Yes, this line is operated under bi-directional ABS with track warrants establishing movement authority. Because the signals entering the single track segment are absolute, I suspect that they will stay at Stop if an opposing movement is anywhere in the block, however some central authority would still need to determine passing points, hence the Track Warants. Under NS this is known as Rule 271 operation, compared with Rule 251 (ABS) and Rule 261 (CTC). Out west this is known as ABS-TWC. You are also correct that the Diverging Clear is what threw a lot of people off. Out west one typically has a single signal located past the spring switch or it has two single head signals able to display Clear, since each signal governs only one route. NS is a bit odd as it is the one major route signaled railroad in the east. Eastern speed signaled lines use diverging route signals over trailing switches to communicate the speed of the switch. Route signaled railroads will put the speed of the switch in the timetable then rely on route knowledge instead of the signal. NS combines the two philosophies and used Diverging Clear to remind the engineer that he is lined up over a reduced speed turnout. Thank you everyone for playing! You can find more information on my blog Log in to reply The following users said thank you: Hawk777, MrTkl |
| Signaling Puzzle 16/09/2016 at 17:54 #84995 | |
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Hawk777
386 posts |
Thanks for the puzzle! I have relatively little experience with North American signalling (despite living there). That might have been an advantage, actually, not knowing that such a thing was considered unusual (two clears is pretty much what a pair of automatic signals would have to read through a spring point onto a clear section). Most of my experience is driving some California-area tracks in the Run8 train simulator, and that area uses route signalling which is why the diverging clear confused me.
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