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Signal aspect sequence - New England to Peterborough

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Signal aspect sequence - New England to Peterborough 19/07/2020 at 19:19 #129780
VInce
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Hi all,

Not sure about this one. There's probably a good explanation for this to do with overlaps, line speed and signal spacing but I'll ask the question anyway.

During a session I cleared a route straight into P2 from P468. Later, with a train approaching P486 at New England North, I pulled out the route at P468 in favour of a shunt P1 to UML (VANS) at Peterborough South. The route P486 to P436 into P2 dropped, as I expected it to, but the signal in rear of P468, P474 reverted from single yellow to red causing an ACOA at P486 in front of 1A40.

I'd assumed that since P468 is approach controlled into P2 anyway and that it hadn't cleared to a proceed then no signals in rear of it would be affected. I was wrong, clearly.

Attached, if needed is a save. Just pull out the route at P468 when 1A40 is approaching P486.

Is this correct behaviour?

Vince

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Last edited: 19/07/2020 at 19:26 by VInce
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 19:31 #129781
postal
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Dear me! Pulling the route to do a shunt in front of the NE UP TPO. I thought you would have known better. The TPO's got enough dwell time at Peterborough for you to get the vans out of the way while the TPO is at the platform.
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 19:34 #129782
VInce
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postal in post 129781 said:
Dear me! Pulling the route to do a shunt in front of the NE UP TPO. I thought you would have known better. The TPO's got enough dwell time at Peterborough for you to get the vans out of the way while the TPO is at the platform.
Yes, I know, its been a long day - before anyone else tells me, it was my own timetable as well.

My school reports always said "can do better". They were right!


Vince

I walk around inside the questions of my day, I navigate the inner reaches of my disarray, I pass the altars where fools and thieves hold sway, I wait for night to come and lift this dread away : Jackson Browne - The Night Inside Me
Last edited: 19/07/2020 at 19:35 by VInce
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 19:40 #129783
JamesN
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There is indeed double-red protection on the Up Fast there
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 20:13 #129784
VInce
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JamesN in post 129783 said:
There is indeed double-red protection on the Up Fast there
Thank you - the intriguing thing then is why does the route drop with the facers into P2 reverse - i.e the slowest route?

I don't know the distances involved and but there is clearly a very good reason for this.

Interesting though....

Vince

I walk around inside the questions of my day, I navigate the inner reaches of my disarray, I pass the altars where fools and thieves hold sway, I wait for night to come and lift this dread away : Jackson Browne - The Night Inside Me
Last edited: 19/07/2020 at 20:14 by VInce
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 20:25 #129785
Albert
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That is indeed correct, double red protection is used to avoid overshooting a signal when no onward route is set and the points might be set into any platform, occupied or not.

Signal 474 even clears if you set a shunt route into the station.

It is arguably somewhat counterintuitive that a train gets an ACOA by cancelling an approach controlled route while its signal is still showing red.

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Last edited: 19/07/2020 at 20:26 by Albert
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 20:58 #129786
clive
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Short answer: yes, it's correct.

Long answer: some years ago we had a meet at Peterborough and Geoff, I think, organized us a visit to the PSB the following morning. I have a load of photos (many blurred) of the panel. There are four typed pieces of paper held on by short grey magnetic strips at appropriate places.

P468 SIGNAL
When timing off please note that P474 signal will also return to red.
Time to release routes on this signal are now all 3 minutes regardless of route type.

P474 SIGNAL
Please note this signal is held at red until P468 routes have been set or 7725 Track occupied.
Failure of TPWS will indicate as Lamp Out.

P486 SIGNAL
When timing off please note that P494 signal will also return to red.
Time to release routes on this signal are now all 3 minutes regardless of route type.

P494 SIGNAL
Please note this signal is held at red until P486 routes have been set or 7824 Track occupied for 4 seconds.
Failure of TPWS will indicate as Lamp Out.

There's also another one:

If we know a loco consist is more than one loco car will let Kings Dyke signaller know how many locos.
This is due to a special bell code required from Kings Dyke to Whittlesea.

and then handwritten underneath:

This is only needed if 6 (six) or more coupled.

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Signal aspect sequence - New England to Peterborough 19/07/2020 at 21:25 #129787
VInce
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Peter,

Most interesting - its certainly counter-intuitive.

A combination of a high line speed and short signal spacing is maybe the reason its done like this.

Thank you.

Vince

I walk around inside the questions of my day, I navigate the inner reaches of my disarray, I pass the altars where fools and thieves hold sway, I wait for night to come and lift this dread away : Jackson Browne - The Night Inside Me
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 21:37 #129791
Steamer
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Presumably, the assessment was that maintaining the double red protection for diverging routes was excessive (extra delay to approaching trains), hence the signal in rear clearing if a route is set from the first signal.

There are examples on other simulations where the double red protection is maintained. Carlisle in particular has examples of both set-ups.

Vince said:
A combination of a high line speed and short signal spacing is maybe the reason its done like this.
As I understand it, that's generally the reason. If I remember rightly, a number of locations on the WCML had double-red protection retro-fitted to existing layouts when the higher (tilting) speed limits for 390s and 221s were introduced.

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Last edited: 19/07/2020 at 21:39 by Steamer
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Signal aspect sequence - New England to Peterborough 19/07/2020 at 22:43 #129796
clive
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Steamer in post 129791 said:

Vince said:
A combination of a high line speed and short signal spacing is maybe the reason its done like this.
As I understand it, that's generally the reason. If I remember rightly, a number of locations on the WCML had double-red protection retro-fitted to existing layouts when the higher (tilting) speed limits for 390s and 221s were introduced.
On the Down Fast at Peterborough there's quadruple red protection: 423, 435, and 473 are all approach controlled unless a route is set from 477. So you can have the route set all the way through the station area on the DF but still get a single yellow at Fletton. Try it.

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Signal aspect sequence - New England to Peterborough 20/07/2020 at 00:11 #129797
Tempest Malice
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clive in post 129796 said:
On the Down Fast at Peterborough there's quadruple red protection: 423, 435, and 473 are all approach controlled unless a route is set from 477. So you can have the route set all the way through the station area on the DF but still get a single yellow at Fletton. Try it.
Not only did this inspire me to try it, but I then noticed that while cancelling 477 did cause 435 to revert to danger, 423 or 435 did not; but looking at a "convenient" copy of the actual SSI data it does appear that this is as per reality. (I wonder if this is to reduce the length of railway that the ACOA could affect, or just to simplify the approach locking lookback data? Though I don't suppose we will ever really know an actual reason why.)

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Signal aspect sequence - New England to Peterborough 21/07/2020 at 17:06 #129847
clive
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Tempest Malice in post 129797 said:

but looking at a "convenient" copy of the actual SSI data it does appear that this is as per reality.
I didn't have access to the SSI data, or even the locking tables; I tested this by having the signaller push and pull the buttons on the real panel.

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