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3 Aspect > 4 aspect

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3 Aspect > 4 aspect 02/12/2019 at 08:58 #122031
jem771
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89 posts
If a train is running on 3 aspect signals and its moving into a 4 aspect zone
if the first 4 aspect signal is showing single yellow what would the preceeding 3 aspect signal show? Green or Single yellow?

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3 Aspect > 4 aspect 02/12/2019 at 09:57 #122032
jc92
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2726 posts
Green. The aspect sequence works as normal so the previous signal would be sited braking distance from the signal in question then the signal in question will be able to display YY and so won't be sited breaking distance from the following signal.
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3 Aspect > 4 aspect 02/12/2019 at 14:40 #122037
Late Turn
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652 posts
The current preference seems to be to insert a three-aspect distant signal (Y/YY/G) before the first four-aspect signal, the last three-aspect stop signal then being capable of showing R/YY/G instead. Most older installations seem to have full braking distance from the first four-aspect signal to the second, the downside being that the distance from a YY at that first signal to a R at the third is significantly greater than the braking distance required.

Either way, the last three-aspect stop signal can show a green with the first four-aspect stop signal showing one yellow. There's probably an exception somewhere, where the first four-aspect stop signal is approach released from red if the next signal is at danger...

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3 Aspect > 4 aspect 02/12/2019 at 18:27 #122040
GeoffM
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4650 posts
In addition, two consecutive signals displaying Y at the same time is non-preferred. There are exceptions.
SimSig Boss
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3 Aspect > 4 aspect 04/12/2019 at 00:52 #122057
bill_gensheet
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350 posts
Not 3 to 4 aspect, but Chelmsford has Y on to Y with 715 and 725, as they are so close.
715 then goes straight to G when 725 is YY

Cannot recall if 711 is Y with 715 Y and 725 R, or if 715 and 725 both sit R until both go to Y.

https://www.opentraintimes.com/maps/signalling/geml3#T_CHLMSFD

Bill

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