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| Approach Control 23/06/2012 at 20:22 #33300 | |
Steamer
3984 posts 
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Hi all, At a junction, what determines whether flashing yellows or release from red is used? Is it calculated by the difference between the turnout speed and the main line speed, or is it decided by operating convenience against the additional circuit complexity of having flashing yellows? "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 |
| Re: Approach Control 23/06/2012 at 21:10 #33302 | |
GeoffM
6376 posts |
You're right in that flashing yellows increases the circuitry required (or ladder logic, or CBI logic), but it's the differential between turnout speed and main line speed that's the factor. It was something like a maximum 1/3 difference (eg 90mph/60mph main/crossover flashing yellow; 90mph/50mph would be approach controlled). However, older installations differ - I remember Swindon station had 25mph crossovers and 80mph on the through line, but had flashing yellows for both through platform routes.
SimSig Boss Log in to reply The following user said thank you: Steamer |
| Re: Approach Control 23/06/2012 at 21:20 #33304 | |
Firefly
521 posts |
Yep depends on speed differential. GK/RT0045 section 5.2 gives details. FF Log in to reply The following user said thank you: Steamer |
| Re: Approach Control 24/06/2012 at 09:47 #33318 | |
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Stephen Fulcher
2078 posts |
The new crossover at Aynho (BS399 points) to allow the Down Bicester line to be worked in the Up direction is 40mph, with the main line 90mph. There are both flashing yellows and preliminary route indicators for that route at BS104R and BS108 signals. The Up Main line towards Oxford and the Up Bicester line both have straight greens (with a position 2 route indicator for the Up Bicester at BS104). There are PRIs for both of these routes as well. The route into the Up Goods Loop (15mph) remains approach released from red. I do not know if there is something to do with the PRIs that allows flashing yellows at slow speed, but was most surprised to see it. Log in to reply |
| Re: Approach Control 24/06/2012 at 09:55 #33319 | |
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Steamer
3984 posts
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Thanks for the replies. For anyone interested, the speeds where flashing yellows are allowed from GK/RT0045, linked in Firefly's post, are: Main route: 80mph-125mph, turnout: greater than 40 mph Or Main route: 40mph- 75mph, turnout: 25mph- 40mph. "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 |
| Re: Approach Control 10/07/2012 at 12:49 #33785 | |
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clive
2789 posts |
" said:I do not know if there is something to do with the PRIs that allows flashing yellows at slow speed, but was most surprised to see it.There's a general trend in the standards to allow things that used to be forbidden if a proper risk assessment has been done and mitigation measures are in place. In this case, a PRI makes it significantly less likely that a driver will misunderstand the speed limit associated with the flashing yellows. Log in to reply |