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| 4 aspect signal failures 17/06/2014 at 16:51 #61778 | |
Jay_G
52 posts |
Evening all, A quick question. In a 4 aspect area, if a signal loses one of its yellows, what happens? My understanding is: If its the top yellow that goes (it isnt lamp proved correct?) then the previous signal will be unaffected IE it will still show a green and give an incorrect sequence of aspects. If its the bottom yellow that goes, the top yellow stays illuminated but the previous signal is held at red? Thanks all Jay Log in to reply |
| 4 aspect signal failures 17/06/2014 at 17:25 #61780 | |
Gwasanaethau
509 posts |
I am just guessing here, but if the top yellow fails then that signal would effectively be showing a single yellow. I would imagine that the previous signal would then drop to double-yellow rather than green in order to keep the sequence correct. I am thinking that a green straight into a single-yellow in a four-aspect area would probably be considered an adverse change-of-aspect by the driver (even if no ‘change’ actually occurred) and would probably result in the driver not being able to brake in time for what they think will be a red at the next signal, whereas at least a double-yellow will at least give them forewarning and they’ll be braking gently in anticipation of the red signal beyond the failed one (which, of course, will probably be single-yellow in the example). As to what actually happens, someone else will have to fill you in, I’m afraid! Log in to reply |
| 4 aspect signal failures 17/06/2014 at 17:25 #61781 | |
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AndyG
1835 posts |
" said:If its the top yellow that goes (it isnt lamp proved correct?) then the previous signal will be unaffected IE it will still show a green and give an incorrect sequence of aspects.I'd be surprised if that was the case, as a driver at full line speed would not see a YY aspect in the sequence(preliminary caution) and could have inadequate braking distance. The whole essence of 4 aspect MAS is to give the necessary 2 blocks braking distance on higher speed lines where 3 aspect would be insufficient. I can only help one person a day. Today's not your day. Tomorrow doesn't look too good either. Log in to reply |
| 4 aspect signal failures 17/06/2014 at 17:28 #61782 | |
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Late Turn
696 posts |
" said:" said:If its the top yellow that goes (it isnt lamp proved correct?) then the previous signal will be unaffected IE it will still show a green and give an incorrect sequence of aspects.I'd be surprised if that was the case, as a driver at full line speed would not see a YY aspect in the sequence(preliminary caution) and could have inadequate braking distance. The whole essence of 4 aspect MAS is to give the necessary 2 blocks braking distance on higher speed lines where 3 aspect would be insufficient. It does give adequate braking distance though - the signal is supposed to be showing YY, so the next will be Y at worst. Obviously that won't do much for the driver's immediate state of mind, but it fits my understanding of how it works, on older installations at least. Log in to reply |
| 4 aspect signal failures 17/06/2014 at 17:56 #61783 | |
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Jay_G
52 posts |
The main reason I am asking was because I was recently told that the top yellow is not lamp proved (which I was a bit sceptical about) so the previous signal would not know if it was showing the correct YY or Y (again, on older installs at least). It would just involve the driver reporting a signalling irregularity, but not involve the form filling as its clearly right side, and then the signaller treating it as failed (not letting trains approach it unless its meant to show Y/R/G, but not approach if its meant to be showing YY
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| 4 aspect signal failures 17/06/2014 at 21:16 #61790 | |
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Firefly
521 posts |
As you guessed. The top yellow is not lamp proved therefor if it fails the signal in rear will remain at Green. It's a right side failure, the driver may be somewhat startled and will make a full brake application, but the next signal will still be showing a single yellow. If the bottom lamp fails it will cause the signal in rear to revert to a single yellow or red depending on the vintage of the area. Flashing Yellows are different and a lamp failure on the top aspect of a flashing yellow will be detected. FF Log in to reply The following user said thank you: Gwasanaethau |
| 4 aspect signal failures 04/07/2014 at 11:24 #62428 | |
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button_pusher
56 posts |
We were recently asked after a top yellow failure (which caused miniscule delay) whether it would be feasible to introduce lamp proving/fff to our signals...
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| 4 aspect signal failures 04/07/2014 at 18:32 #62435 | |
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Firefly
521 posts |
Nearly all 4 aspect signals have first filament failure detection on the top yellow. It's just lamp proving that is not provided. If your techs are keeping on top of filament failures it shouldn't come to a lamp failure. ( that said your failure may not have been caused by a blown first filament. ) FF Log in to reply |
| 4 aspect signal failures 05/07/2014 at 06:20 #62442 | |
BarryM
2158 posts |
" said:As you guessed.Aren't Drivers taught the road to know what each signal will show on all their routes? Something wrong if they are not! Barry Barry, Sydney, New South Wales, Australia Log in to reply |
| 4 aspect signal failures 05/07/2014 at 08:01 #62450 | |
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Late Turn
696 posts |
Yes, but they'll still be somewhat startled if they suddenly find a signal showing a more restrictive aspect than it should under the correct aspect sequence! If the top yellow fails in a signal that should be displaying YY, they'll encounter G - Y - Y - R, but will be expecting to find the third signal at danger (and probably unable to stop at it) after passing the second.
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| 4 aspect signal failures 05/07/2014 at 08:12 #62451 | |
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maxand
1637 posts |
Without wishing to stray too far off-topic, won't all this be a thing of the past once they replace filaments with LEDs?
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| 4 aspect signal failures 05/07/2014 at 09:58 #62461 | |
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Lardybiker
771 posts |
As an electronics engineer I can tell you that whilst LED's are more reliable then filament bulbs, they are not infallible and do fail, so no it won't become a thing of the past....It just will be less often.
Last edited: 05/07/2014 at 09:59 by Lardybiker Log in to reply |
| 4 aspect signal failures 05/07/2014 at 10:03 #62462 | |
Steamer
3927 posts |
Going even further off topic... How are lamps proved lit? Is there a relay in series with the lamp to confirm current is flowing?
"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 aspect signal failures 05/07/2014 at 14:18 #62476 | |
DriverCurran
683 posts |
" said:" said:Trust me as a former driver when you are doing 70 mph on a downhill gradient and suddenly faced with a single yellow aspect where you are expecting at the very least to find two yellows, the first thing in your mind is 'Where did I miss the signal showing two yellows and the potential consequences of suffering a SPAD' and not 'Oh the top yellow has failed on that signal'. Luckily in my case the officer had pulled the route owing to an incident further down the line, but even so you still have the thought that you as a driver have made a very very big error.As you guessed.Aren't Drivers taught the road to know what each signal will show on all their routes? Something wrong if they are not! Paul You have to get a red before you can get any other colour Log in to reply The following users said thank you: BarryM, atari001, maxand |
| 4 aspect signal failures 05/07/2014 at 14:28 #62477 | |
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Stephen Fulcher
2029 posts 
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Steamer, that is exactly how lamp proving tends to be done. The top yellow being out is not unsafe as the next signal will still be showing a yellow anyway, hence not requiring to be proved, but it does have the potential to worry drivers. It is also possible that it would take a while before anyone reported it as a fault. Log in to reply The following user said thank you: Steamer |