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Approach Control Signals Release Point

You are here: Home > Forum > Miscellaneous > The real thing (signalling) > Approach Control Signals Release Point

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Approach Control Signals Release Point 26/12/2011 at 22:00 #26218
quickthorn
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23 posts 		On a diverging junction with, say, approach control from red, when would the junction signal release from red? In general, would the driver of an approaching train see the signal release, or would it release before it was visible?

The reason I'm asking is that I'm building a route for Railworks3 and this has a few approach controlled junctions. However, approach controlled signals in Railworks are released when the train goes over the AWS ramp, so the driver sees a red aspect, which drops to green (if it can) at the exact moment that the AWS warning horn sounds in the cab. I'm not sure if that's accurate, to be honest.
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Re: Approach Control Signals Release Point 26/12/2011 at 22:03 #26219
GoodbyeMrFish
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148 posts 		i think this is just down to the locality of the junction making sure the train slows down enough for however sharp the exit will be. in some places the driver would see the signal pull off.
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Re: Approach Control Signals Release Point 26/12/2011 at 22:44 #26222
Steamer
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3984 posts 		The signal is released based on how long the train has occupied a track circuit for. This is based on how low the turn-out speed is compared to the straight ahead speed. The track circuit is usually the one approaching the signal, however it may be any circuit between it and the previous signal. For example, on the Saltley Sim, signal 158 (near Tysley) releases towards 166 7 seconds after the track circuit immediately before it (T324) is occupied, however 142 (near Dorrige) towards 144 10 seconds after the track circuit immediatley before it (T286) is occupied. However, signal 44 (near Kings Norton) releases towards signal 62 the moment either the track circuit before it (T144) or the circuit before that (T96) is ocuupied. The signal releasing as the driver passes the AWS magnet is probably inaccurate, as the signal releases according to how long the track circuit has been occupied, not an exact point on the track.
"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)
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Re: Approach Control Signals Release Point 27/12/2011 at 00:39 #26225
guyh
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54 posts 		My understanding, possibly to be proved wrong by the knowledge on the forum(!), is that the signalling designer will calculate how long a train will be on each track circuit if braking from line speed to the red signal at the junction and release the signal at the point that the train on such a braking curve will have reduced to the turnout speed (or a bit later if that's cheaper). The designer could specify occupation of a track circuit, or a timer associated with occupation of a track circuit. The basic intent is to ensure a sensibly driven train will see a red until the train reduces to the junction turnout speed. Of course a modern driver is likely to brake earlier and be much slower by this point.

At the point the signal clears it will usually be restricted to yellow until the AWS is passed so that a warning is received. I don't know whether that is achieved by track circuits plus timers or not.
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Re: Approach Control Signals Release Point 27/12/2011 at 09:04 #26229
Firefly
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521 posts 		All answers are correct here.

The timing is based on the length of the track circuit.

More info can be found Here

A lot of the latest standards are only available internally, however the old standards are freely available on the rgsonline website.

The older standard used to say:
Quote:
B10.8.2
The junction signal shall clear from red to a higher aspect (as determined by the aspect displayed at the signal ahead) when the approaching train has passed the single yellow and reached a position from which the route indication and main signal are both readable – see GK/RT0031, Issue 4, Table 16. Wherever possible, this shall be before reaching the associated AWS.
This link (also a withdrawn standard) has details of how the timing is determined.

To save you trawling through this is the table:-



So basically it all depends on the readability of the signal.

PLJI's (aka Feathers) are readable at 800m (the same as colour light signal aspects) and therefore the signal will normally release the moment the train passes the yellow signal (remember we rely on drivers route knowledge to control the train to a speed suitable for the route they are taking)

Theatre Route Indicators are readable at 250m and we shouldn't allow the signal to step up from red until the train is within 250m of the signal.

FF
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Re: Approach Control Signals Release Point 27/12/2011 at 11:33 #26231
Zoe
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252 posts 		" said:
PLJI's (aka Feathers) are readable at 800m (the same as colour light signal aspects) and therefore the signal will normally release the moment the train passes the yellow signal (remember we rely on drivers route knowledge to control the train to a speed suitable for the route they are taking)

Based on the standard above though, wouldn't this require the junction signal to be visible to the driver immediately after they have passed the signal in rear?
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Re: Approach Control Signals Release Point 27/12/2011 at 14:02 #26248
Firefly
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521 posts 		Quote:
Based on the standard above though, wouldn't this require the junction signal to be visible to the driver immediately after they have passed the signal in rear?
It's not a requirement that the driver can see it at 800m, it's only a requirement that the driver can clearly read the route indication at the same time as the signal changes aspect.

Because PLJI's and colour light signals are both readable at 800m there's no danger of a driver sighting the green aspect prior to seeing the route indication so the junction signal is allowed to clear the moment the train passes the signal in rear at yellow. It doesn't matter if the driver sees it at 800m or 200m.

Theatre indicators are only readable at 250m so the signal must not be allowed to clear until the train is judged to be within 250m of the signal (this often achieved with a track circuit section rather than timing)

Miniature indicators used with sub signals are only readable at 100m so the signal clearance must be delayed until the train is either timed to stand or measured with a short track circuit.

Hope this makes sense

FF
Last edited: 27/12/2011 at 14:33 by Firefly
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Re: Approach Control Signals Release Point 27/12/2011 at 14:03 #26250
Stephen Fulcher
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2078 posts 		A driver is not required to "sight" a signal until seven seconds before he would pass it if he were travelling at linespeed, generally speaking.

There is of course nothing to say that he cannot be allowed to see it long before that, and in most cases can.
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Re: Approach Control Signals Release Point 27/12/2011 at 14:06 #26251
Zoe
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252 posts 		Quote:

the approaching train has passed the single yellow and reached a position from which the route indication and main signal are both readable

This standard certainly gives the impression that the requirement is for both the route indication and the main signal to be readable before the signal can clear. This wouldn't be guaranteed to be 800 metres if the line was not straight.
Last edited: 27/12/2011 at 14:09 by Zoe
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Re: Approach Control Signals Release Point 27/12/2011 at 14:08 #26253
Stephen Fulcher
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2078 posts 		It is indeed.

As FireFly has stated above, no signal will be allowed to clear to an aspect that requires a route indication of any nature until the driver of a train is in a position where the route indicator can be read clearly.

It is a maximum distance from the signal, there is nothing to say that the train cannot be closer as the signal and route indicator will both be "readable"
Last edited: 27/12/2011 at 14:09 by Stephen Fulcher
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Re: Approach Control Signals Release Point 27/12/2011 at 14:14 #26254
Zoe
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252 posts 		" said:
As FireFly has stated above, no signal will be allowed to clear to an aspect that requires a route indication of any nature until the driver of a train is in a position where the route indicator can be read clearly.

Firefly was saying that the junction signal would immediately clear when the train passes the signal in rear. The standard though clearly requires the train to be at a position where both the signal and junction indicator are readable before it can be cleared. If the line is not straight then I would have said there would certainly be some cases where they were not readable at 800 metres.
Last edited: 27/12/2011 at 14:36 by Zoe
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Re: Approach Control Signals Release Point 27/12/2011 at 14:16 #26255
quickthorn
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23 posts 		Thanks for all that, it's helped a lot. Firefly, that link is incredibly useful. The table you've put up is just what I wanted for a subsidiary signal I've got to place, but there's another table further on which gives all the times for junction signals at various distances.

I've actually got a cab ride DVD for part of this route, and this shows a train turning off from 60 to 20. From a standing start at Worksop on passing the down platform end signal WP535 at single yellow, the next signal isn't visible on the DVD until the route indicator lights up about 1 minute after passing the platform end. When we get there, we can see it's a green aspect as well. This all fits in with what's been said, on the whole, although I don't think the Worksop sim version of that signal WP533 has approach control at all.

Just one more question: from that guidance, it seems that a junction signal should clear to a green aspect, but are there any situations where the aspect would be restricted to yellow?
Last edited: 27/12/2011 at 14:19 by quickthorn
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Re: Approach Control Signals Release Point 27/12/2011 at 14:31 #26257
Firefly
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521 posts 		Quote:
Just one more question: from that guidance, it seems that a junction signal should clear to a green aspect, but are there any situations where the aspect would be restricted to yellow?
Yes, if the signal beyond the junction is at red.
Last edited: 27/12/2011 at 14:32 by Firefly
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Re: Approach Control Signals Release Point 27/12/2011 at 14:34 #26258
Zoe
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252 posts 		" said:
Just one more question: from that guidance, it seems that a junction signal should clear to a green aspect, but are there any situations where the aspect would be restricted to yellow?

At Dawlish Warren going into the Down Loop you will only get a single yellow. I was told by a manager this was to do with a risk of reading through although I haven't seen anything official stating this. It was also about 10 years ago so it could have changed since then.
Last edited: 27/12/2011 at 14:37 by Zoe
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Re: Approach Control Signals Release Point 27/12/2011 at 14:45 #26261
Firefly
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521 posts 		The latest version of gk/rt0045 doesn't mention readability, it says

Quote:
The junction signal shall display the red aspect until the approaching train is detected to have:
a) Passed the junction distant signal, and
b) Passed the banner signal (where provided with the junction signal), except where a splitting banner signal aspect is displayed.
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Re: Approach Control Signals Release Point 27/12/2011 at 14:49 #26262
Firefly
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521 posts 		Zoe, Dawlish Warren scenario:
As mentioned here, however the yellow I acheived because the next signal is red.

Quote:
Table 22 Methods of junction signalling
5.2.1.2 Where the risk of reading through at an approach controlled junction signal (that is to say, method 3 or method 4 in Table 22) is unacceptable, the first signal beyond the junction on the straight ahead route and any other diverging route shall be maintained at its most restrictive aspect until the train has passed the junction signal.
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Re: Approach Control Signals Release Point 27/12/2011 at 14:52 #26263
Zoe
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252 posts 		" said:
Zoe, Dawlish Warren scenario:
As mentioned here, however the yellow I acheived because the next signal is red.
The question here is if "any other diverging route" includes the route taken.

As for approach controlled signals in general, I've certainly seen cases where signals have feathers and the signal doesn't clear until the train is very close to it so either the standards have recently changed to not be so restrictive or it was decided to have much stricter rules than what the actual standards say when these were installed.
Last edited: 27/12/2011 at 15:51 by Zoe
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Re: Approach Control Signals Release Point 27/12/2011 at 15:26 #26265
Firefly
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521 posts 		Quote:
The question here is if "any other diverging route" includes the route taken.
It does if it represents a read through risk.

Quote:

As for approach controlled signals in general, I've certainly seen cases where signals have feathers and the signal doesn't clear until the train is very close to it so either the standards have recently changed to not be so restrictive or it was decided to have much stricter rules than what the actual standards say when these were installed.
The standards do constantly change. It is possible that the approach control on your examples were subject to restricted overlaps or the sighting committee recommended a more restrictive arrangement
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Re: Approach Control Signals Release Point 29/12/2011 at 09:49 #26380
Forest Pines
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525 posts 		" said:

As for approach controlled signals in general, I've certainly seen cases where signals have feathers and the signal doesn't clear until the train is very close to it so either the standards have recently changed to not be so restrictive or it was decided to have much stricter rules than what the actual standards say when these were installed.
My local station is Stapleton Road, so I often see the timing of signal B235 as it clears for an Avonmouth train - the aspect is always green with a feather, as the next signal is B351R at Montpelier. I assume, given the distance from B235 to Narroways Hill Junction, that it has a full overlap. The normal behaviour seems to be that B235 clears just as the approaching train is passing B235's banner repeater. As I'm usually by the signal waiting for the train, I'm not sure whether the driver will see the banner repeater clear, but my feeling is that normally he/she doesn't. There is a rather tight speed restriction on the diverging route at the junction, but the distance from signal to junction is such that branch trains can speed up quite a bit on leaving Stapleton Road before having to brake for the junction.
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Re: Approach Control Signals Release Point 30/12/2011 at 17:23 #26477
Stephen Fulcher
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2078 posts 		There is a good chance from the sounds of it that there is a track circuit between the banner and the signal itself (not necessarily indicated separately on the panel) which releases the signal route.
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Re: Approach Control Signals Release Point 31/12/2011 at 00:06 #26509
Firefly
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521 posts 		Quote:
The normal behaviour seems to be that B235 clears just as the approaching train is passing B235's banner repeater.
It's another requirement of the standard.

Quote:

Junction method 3: Approach control from red
5.2.4.1 Where it is not appropriate to use a less restrictive method, the signalling system shall be configured to display a cautionary aspect sequence leading up to approach control from red at the junction signal.

5.2.4.2 The junction signal shall display the red aspect until the approaching train is detected to have:
a) Passed the junction distant signal, and
b) Passed the banner signal (where provided with the junction signal), except where a splitting banner signal aspect is displayed.
Read Junction distant signal as "Signal in rear of the junction signal"
Last edited: 31/12/2011 at 00:07 by Firefly
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Re: Approach Control Signals Release Point 08/02/2012 at 20:59 #29156
Forest Pines
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525 posts 		Sorry to resurrect this thread after 6 weeks, but this evening I finally had the chance to observe B235 more closely, and found that I was wrong above, and it doesn't follow the standard. I was travelling in the first carriage of a Severn Beach train, and could see the repeater for B235 clearly: it cleared when the train was about 100 yards in rear of the repeater, well after it had come into view, but (considering the speed of the train) with plenty of time for the driver to see it showing off.

I was looking out for it, because I'd already noticed no sign of any train detection equipment near the repeater itself - there is an IRJ at the signal itself, but no other IRJs or signs of other types of TC end in the area.
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Re: Approach Control Signals Release Point 09/02/2012 at 08:28 #29181
GeoffM
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6376 posts 		" said:
Sorry to resurrect this thread after 6 weeks, but this evening I finally had the chance to observe B235 more closely, and found that I was wrong above, and it doesn't follow the standard. I was travelling in the first carriage of a Severn Beach train, and could see the repeater for B235 clearly: it cleared when the train was about 100 yards in rear of the repeater, well after it had come into view, but (considering the speed of the train) with plenty of time for the driver to see it showing off.

I was looking out for it, because I'd already noticed no sign of any train detection equipment near the repeater itself - there is an IRJ at the signal itself, but no other IRJs or signs of other types of TC end in the area.
It's probably timed occupation of the track section then. If, the next time you see it, it clears at a slightly different place then this would confirm it.
SimSig Boss
Last edited: 09/02/2012 at 08:28 by GeoffM
Reason: circuit/section
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Re: Approach Control Signals Release Point 09/02/2012 at 16:13 #29211
Firefly
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521 posts 		Quote:
and it doesn't follow the standard
The standards that I quoted were modern standards, Bristol is an E10K (E Ten Thousand) installation from the 60's.

Here's an extract from the E10k standards:-



As you can see the preference was for track timers so that the signal doesn't always release at exactly the same point.
Last edited: 09/02/2012 at 16:14 by Firefly
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