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Ockendon branch - why some 3-aspects in with the 2-aspects?

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martin2345uk

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Going along the Ockendon branch in C2C land in the Up direction, you have a 2-aspect distant signal, followed by its 2-aspect stop signal, followed by a 3-aspect distant and its 3-aspect stop signal controlling entry into the Ockendon station passing loop... followed again by a 2-aspect stop signal at the end of the platform.

What would be the reason for the 2 3-aspect signals here? I am sure it's an obvious reason but it's eluding me...
 
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edwin_m

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Going along the Ockendon branch in C2C land in the Up direction, you have a 2-aspect distant signal, followed by its 2-aspect stop signal, followed by a 3-aspect distant and its 3-aspect stop signal controlling entry into the Ockendon station passing loop... followed again by a 2-aspect stop signal at the end of the platform.

What would be the reason for the 2 3-aspect signals here? I am sure it's an obvious reason but it's eluding me...
The positioning of stop signals is determined by where trains need to stop, particularly on single lines where one is needed on the approach to the entry and exit of each passing loop.

If this positions the stop signals at a lot more (usually >50% more I think) than braking distance then a separate two-aspect distant will be provided. Giving a single yellow a long way before the red is a bad idea operationally (unnecessarily slowing the train when it might have got a clear run if the distant was closer to braking distance) and safety-wise (driver might forget the yellow if they didn't have to act on it for a while). If the stop signals are only somewhat more than braking distance apart then the distant of the second one will be combined with the first one to give a three-aspect signal. If they have to be at less than braking distance then there may be a signal capable of displaying double yellow.
 

martin2345uk

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Thank you! Will have to read through that a few more times till it's completely clear in my head but yes it does make sense :0)
 

HSTEd

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Honestly I always struggle with the concept of separate distants and local signals.

But I think I understand it now, although I thought it was primarily a relic from the semaphore era and most colour lights signals displayed all aspects?
 

High Dyke

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Looking at the map. Does the 3-aspect signal have a route indicator on it, to advise which platform you are going to? It may be a 3-aspect as you could in theory have a train that is not stopping at Ockenden, which would want green aspects and not adverse signals for the fastest possible route.
 

martin2345uk

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Looking at the map. Does the 3-aspect signal have a route indicator on it, to advise which platform you are going to? It may be a 3-aspect as you could in theory have a train that is not stopping at Ockenden, which would want green aspects and not adverse signals for the fastest possible route.
It does indeed have a route indicator... but I don't quite understand what you mean as to why that means it would have to be 3 aspect...?
 

High Dyke

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It does indeed have a route indicator... but I don't quite understand what you mean as to why that means it would have to be 3 aspect...?
Basically, a train may take either route from the signal into a platform. If the junction signal was two aspect then it would only be able to show a stop (Red) or proceed (Yellow or Green), depending on the aspect of the signal at the end of the platform/loop. A 3-aspect signal would advise the driver give the driver more information. It may be that a train is not booked to stop at the station, therefore the driver would expect to see a green aspect on every signal in that area. If the train is required to stop in the loop/platform then he would receive a yellow aspect at the junction signal followed by a red to protect the platform/loop exit.
 

bluenoxid

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I might have misunderstood the situation and I don’t know it but it sounds like an arrangement that enables flighting of trains. I assume trains will slow for Ockenden so if you have an extra service on the line, it will enable the second train to run in closer but still maintain a reasonable pace.
 

Tomnick

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It’s quite straightforward really.

You need two stop signals. One controls the entry to the loop, protects anything standing in the loop and the pointwork, and gives a route indication if either line can be used. The second controls the exit from the loop, and protects the single line beyond.

The first one needs to be a three-aspect signal because it reads to another stop signal, thus needs a yellow aspect.

If there isn’t braking distance available between the first and second stop signals, you couldn’t have a green in the distant with the second stop signal at danger, because a train wouldn’t be able to stop in time after passing the first stop signal at yellow. One solution would be to hold the first stop signal at danger, and thus the distant at caution, until the train’s closely approaching it and already well under control, but that increases journey times and reduces capacity on the single line: The alternative is to make the distant a three-aspect distant signal, so that you get two yellows in the distant with that second stop signal at danger, and thus (more than) adequate braking distance.
 

martin2345uk

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It’s quite straightforward really.

You need two stop signals. One controls the entry to the loop, protects anything standing in the loop and the pointwork, and gives a route indication if either line can be used. The second controls the exit from the loop, and protects the single line beyond.

The first one needs to be a three-aspect signal because it reads to another stop signal, thus needs a yellow aspect.

If there isn’t braking distance available between the first and second stop signals, you couldn’t have a green in the distant with the second stop signal at danger, because a train wouldn’t be able to stop in time after passing the first stop signal at yellow. One solution would be to hold the first stop signal at danger, and thus the distant at caution, until the train’s closely approaching it and already well under control, but that increases journey times and reduces capacity on the single line: The alternative is to make the distant a three-aspect distant signal, so that you get two yellows in the distant with that second stop signal at danger, and thus (more than) adequate braking distance.
Makes perfect sense thanks mate!!!
 

Shoeburysam

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Makes perfect sense thanks mate!!!
So we have two aspect (red and green) signals on this line because, the next signal is a distant signal and is unable to show a red. So single yellow is not required. The distant signal is then followed by an automatic signal (red, S yellow and green) then a control signal. Due to it being a single line railway that operates in both directions the signalling is different to what you would find on the other routes.

Makes perfect sense thanks mate!!!
For what it's worth the branch is a strange set up. It's probably closer to simbid signalling like the mainline (going down the up or vice versa) then full bi directional like Liverpool St.
 
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