Signals on the network

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Gathursty

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How far apart are they spaced? In particular how quick would you pass from one to the next on a Pendo/Voyager service on the WCML?
 
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michael769

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Depends!

Typically the higher the line speed the wider the spacing - indeed in many cases it is the signal spacing that dictates the line speed.

But the type of signalling also has an impact - 4 aspect signals are usually closer together than 2 aspect ones.

The goal is that a driver on a train travelling at full linespeed should, upon seeing a caution aspect be able to stop his train before passing the signal at danger without having to apply emergency braking.
--- old post above --- --- new post below ---
This seems to be the latest standard for signal spacing

It's a somewhat complex calculation to say the least.
 

The Planner

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Green to Green aspects (ie: a technical headway) can be as low as 75-80 seconds on parts of the southern WCML.
 

Rwhunited

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The signals are spaced differently dependant upon linespeed, minimal is the braking distance of the worst braking train to stop at max linespeed, then if you add a double yellow into the mix then its 2 signals apart
 

jopsuk

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on the London Underground, who run quite different principles for their signalling, signals on approach to a station can be much less than a train length apart.

Meanwhile, out in the wild worlds of rural lines, semaphore signals especially can be quite some distance apart
 

The Planner

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Indeed, stand to be corrected but I think Carnforth to Settle Jn is one of, if not the longest block sections. I know we plan it as AB. That has to be 25 miles long.
 

TDK

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How far apart are they spaced? In particular how quick would you pass from one to the next on a Pendo/Voyager service on the WCML?
Not many signals are the same distance apart as there are many factors considering signal spacing.

1. Line Speed
2. Gradients
3. Sighting
4. Number of aspects
5. Braking distances (related to all the above)

I would say the most governing factors are line speed and gradients - some signals can be more than half the distance apart on an up gradient opposed to a down.
 

notadriver

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Surely the braking distance from full line speed is calculated based a train braking at a yellow signal to the red signal, not on sighting the yellow?
 

notadriver

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on the London Underground, who run quite different principles for their signalling, signals on approach to a station can be much less than a train length apart.
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Apparently tube driving is very different in that they drive 'on sight'. No cautionary aspects. It's either green or red.
 

The Planner

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Surely the braking distance from full line speed is calculated based a train braking at a yellow signal to the red signal, not on sighting the yellow?
I would have expected it to be off the sighting distance otherwise where would the driver reaction time come into it ?
 

TDK

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Surely the braking distance from full line speed is calculated based a train braking at a yellow signal to the red signal, not on sighting the yellow?
Sighting does come into the factor, if a signal is going to be a very poorly sighted signal it will be placed in a more suitable place
 

notadriver

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The 'drive on sight' comment comes from someone I know who has ridden in the cab of tube and NR trains but who isn't a driver. He said that a train could be driving at full line speed on green signals and still be able to stop if the next one was red.
 

jopsuk

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Perhaps mixing up "being able to see the train in front all the time" with "drive on sight"? Drive on Sight is what Trams do on on-road sections, where they follow much the same rules as cars...
 

Cherry_Picker

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The 'drive on sight' comment comes from someone I know who has ridden in the cab of tube and NR trains but who isn't a driver. He said that a train could be driving at full line speed on green signals and still be able to stop if the next one was red.
I think you should take that with a pinch of salt. I cant speak for the entire underground as different systems exist on different lines, but I sign the fast lines of the Met between Harrow and Amersham, and I can assure you that it is clearly not true. Yes, there are parts where the line speed is < 40mph and you can almost certainly stop before a red after running on greens and there are sections where you will be looking at the tail lamps of the train in front of you (this also happens a lot on the busier sections of the National Rail network too)but the signalling system cannot rely on working like that. The parts of the Underground I know well have a very similar to heavy rail two, three our four aspect signalling system.
 

Surreytraveller

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I would have expected it to be off the sighting distance otherwise where would the driver reaction time come into it ?
But sighting distance would vary depending on the weather. The train would still take as long to stop if it was foggy as it would if the weather was clear, so therefore the stopping distance would be from the signal, not from where it is sighted.
 

Metroland

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I think you should take that with a pinch of salt. I cant speak for the entire underground as different systems exist on different lines, but I sign the fast lines of the Met between Harrow and Amersham, and I can assure you that it is clearly not true. Yes, there are parts where the line speed is < 40mph and you can almost certainly stop before a red after running on greens and there are sections where you will be looking at the tail lamps of the train in front of you (this also happens a lot on the busier sections of the National Rail network too)but the signalling system cannot rely on working like that. The parts of the Underground I know well have a very similar to heavy rail two, three our four aspect signalling system.
Indeed, it's all to do with sighting distances. My understanding is on some sections where the line speed is very slow, and you can clearly see the stop signal ahead there is no repeater - unless it's a fog repeater. But generally the underground does have warning signals in much the same way as Network Rail.

http://www.trainweb.org/tubeprune/signalling3.htm
 

Anonywave

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Sighting does come into the factor, if a signal is going to be a very poorly sighted signal it will be placed in a more suitable place
although, of course, they do have those banner (repeater) signals (whatever they call them)
 
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