Jump to content
 

Modern UK Signalling - What do you want to know?


Recommended Posts

Hi,

 

I thought that I'd start a topic where people can ask general questions on Modern UK Signalling that I (or other experts) can answer to avoid clogging up other threads too much!

 

If you have specific question on signalling individual layouts, that's better left to separate topics, but for general questions on signalling layouts, modern signalling principles or interlocking / control questions, you can add them here. Also, if you have questions about other signalling related infrastructure (such as train protection, ATP, ETCS, Selective Door Operation, Power Change-Over etc.), I can have a good go at answering them.

 

Before I start, I'll just explain who I am for those that don't know me and are wandering what qualifies me to answer these questions. I'm a currently a Signalling Principles Designer and hold a IRSE Designers License. I've been working on all manner of signalling schemes, including Mechanical, Colour Light and In-Cab signalling systems for the past 5 years, mostly on the Western Region, but lots of other areas. Obviously I can't give too much details about any of the schemes I've worked on, but I may use them as examples.

 

So, with that, ask away... :) 

 

Simon

Edited by St. Simon
  • Like 7
  • Thanks 1
Link to post
Share on other sites

41 minutes ago, 37038 said:

I've got some of the details somewhere, but could you give a general overview of TPWS grid types and positions (ie distance to signals, bufferstops) please?

 

Hi,

 

I can!

 

TPWS (Train Protection & Warning System) Loops come in two types, standard size loops and mini loops. Standard size loops are used for signals & speed restrictions, whilst mini loops are used for buffer stops (mostly platform buffer stops, but can be used for turnback siding buffer stops etc.). Within each TPWS set up, there are at least two loops, an Arming Loop and a Trigger Loop, they are both physically identical to each other, the difference only being the electrical frequency that is emitted.

 

Below, is my diagram from my book, which gives a more detailed explanation of TPWS (sorry blatant plug I know, but it saves me writing everything out:mosking:)

 

Figure_216.jpg.eefa6df832de1259e56948d27a27d99c.jpg

 

For controlled main aspect signals with a conflict in the route or the overlap (there are rules on which signals are fitted with TPWS, but that description covers most of them), the basic TPWS installation is the 'Train Stop System' or TSS, this consists of an Arming Loop and a Trigger Loop placed at the foot of the signal, immediately adjacent to each other. The TSS does have tolerance on it's position relative to the signal as can be seen in the diagram above, the movement of the Loops within this tolerance are based on the proximity of the signal replacement joint or axle counter to the TSS loops, but the standard position is at the foot of the signal.

 

If it is deemed that a TSS is not sufficient to stop a passenger train with enhanced braking prior to the conflict point (this is now done through a special calculation tool), then up to three 'Over Speed System' or OSS loops can be provided. The Trigger Loop for an OSS is placed between 25m and 450m on approach to the signal it applies to, with the Arming Loop placed between 5m and 23m on approach to the Trigger Loop. The distance between the OSS Trigger Loop and the Signal goes up in 25m steps (i.e. 25m, 50m, 75m etc.), whilst the separation distance between the Trigger and Arming Loops grows by 0.5m for each step the Trigger Loop moves away from the Signal (i.e, if the Trigger is 25m from the signal, the separation is 5m, if the Trigger is at 50m, the separation is 5.5m, if the Trigger is at 75m, the separation is 6m etc.). If more than one set of OSS Loops are provided, the minimum distance between the Arming Loop of the first set and the Trigger Loop of the second is 25m and the maximum is 450m, again going in 25m steps, The separation steps are still counted from the signal though.

 

The same OSS positioning rules are applied for speed restrictions, however OSSs are only provided for speed reductions of a reduction equal to or greater than one third of the approach speed and where the approach speed is greater than 60mph, but they aren't always required. Again, we use a special calculator tool to tell us whether a speed restriction needs an OSS and where it should be.

 

For Buffer Stop OSS loops, the positions are fixed, with the Trigger Loop placed 55m on approach to the buffer stops and then Arming Loop is 5.5m separation from the Trigger Loop.

 

Hope that explains it well enough.

 

Simon

  • Like 1
  • Thanks 1
  • Informative/Useful 2
Link to post
Share on other sites

  • 1 year later...
5 hours ago, Western Aviator said:

Well, fair play to @St. Simon for offering up his knowledge for free when he has also written a book about it. 

 

Hi,

 

Well, there is a lot of stuff that I can't fit into the book (full explanations of ETCS, SDO, APCO etc for instance :) ) but people would like to know.

 

Plus everything keeps changing and needs being kept up to date!

 

Simon

  • Like 2
  • Agree 3
Link to post
Share on other sites

1 minute ago, Stephen Freeman said:

It might seem daft, but as usual most photos etc only show the front of the signals, the backs have to be modelled too you know. At least prototype drawings are available at least for some examples.

 

True, but it is quite difficult to get photos of the rear of signals as a large proportion of them are not in a position where the public could get access to them easily (and I didn't have the ability to access non-public areas easily).

 

Also, the book is more about modelling the layout of signals rather than constructing them, simply because this is the area where information is most lacking. However, for the second edition(s), I am looking at including more about the signal modelling side of things.

 

Simon

  • Like 1
  • Agree 2
Link to post
Share on other sites

6 hours ago, St. Simon said:

 

True, but it is quite difficult to get photos of the rear of signals as a large proportion of them are not in a position where the public could get access to them easily (and I didn't have the ability to access non-public areas easily).

 

Also, the book is more about modelling the layout of signals rather than constructing them, simply because this is the area where information is most lacking. However, for the second edition(s), I am looking at including more about the signal modelling side of things.

 

Simon

Not meant as a criticism of the book but an observation of published photos (book or web) in general

Link to post
Share on other sites

  • 1 year later...

Hi,

 

As a way of a thread bump, for those that want to learn more about Modern UK Signalling Systems, I'll be doing a talk on them tomorrow evening at 19:30 at The Model Railway Club in London, it is a hybrid in person / zoom meeting, so you view from home. If you are interested and want to find out more, see here:

 

Modern & model signalling systems - The Model Railway Club

 

Simon

  • Informative/Useful 1
Link to post
Share on other sites

  • 1 month later...

Are really basic questions allowed here?

 

Am I right in thinking that on modern main lines with 3- or 4-aspect signalling, there is no physical difference between distant and home signals, i.e. any signal can be either?

 

On lines with 2-aspect signalling, are there still physically distinct distant (yellow/green) and home (red/green) signals?

Link to post
Share on other sites

The terms Home and Distant signal relates to conventional (Absolute Block) signalling practice, where signals were provided only at stations (signal boxes), signal spacing being limited by physical constraints imposed by mechanical equipment.

 

Modern Multiple Aspect Signalling (most of the network) is worked under Track Circuit Block regulations where the terms don't really mean anything as signals are spaced more evenly along the line.  The spacing is such that a train travelling at line speed passing a Y can stop before reaching the next signal (3-aspect); or for 4-aspect passing a YY will have sufficient braking distance to stop at the next but one.

 

However, conventional signalling practice can use colour lights to replace semaphores, usually 2-aspect.  A distant would be Y/G only, a Home would typically be R/G, sometimes R/Y.  The equivalent of a semaphore starting signal with the distant arm for the next box underneath it (Home arm above a distant arm) would be a 3-aspect R/Y/G.  The same braking distance considerations apply.

 

  • Thanks 1
  • Informative/Useful 1
Link to post
Share on other sites

20 hours ago, rogerzilla said:

Are really basic questions allowed here?

 

Am I right in thinking that on modern main lines with 3- or 4-aspect signalling, there is no physical difference between distant and home signals, i.e. any signal can be either?

 

On lines with 2-aspect signalling, are there still physically distinct distant (yellow/green) and home (red/green) signals?


Hi,

 

As Micheal Hodgson says, the term ‘Home’ isn’t used in Multi-Aspect Signalling (unless a multi-aspect signal is used as a direct replacement for a semaphore signal), it is replaced with the term ‘Main Aspect’, but the term Distant is still is used, although it is used more in two aspect signalling, but can be seen in 3 and 4 aspect signalling as a ‘Wiltshire Distant’ as part of transitions between aspect sequences.

 

The physical head of a distant signal is the same as any other main aspect signal, with the difference that it doesn’t display a red aspect (unless it is a non-approachable red distant). The other difference is that nowadays Distants have ID plates with an upwards pointing triangles. 
 

Distants are also no longer played with an ‘R’ or ‘RR’ suffix and have separate IDs (unless it is for consistency as part of a minor alteration to an existing area).

 

I hope that helps.

 

Simon

Link to post
Share on other sites

Hi,

 

To expand on Michael’s explanation of braking distance / headway, here is a post from another thread that might be useful:

 

It is a common myth in the hobby that the number of aspects is dictated by the importance of the line, but it’s not true. You start by calculating the headway given by each set of aspect signalling within the given line speed (using the braking distance) and then choose which gives you the better headway than you need.

 

The formula for headway for each aspect signalling is as follows:

 

3 Aspect = [Sighting Distance + (2 x Braking Distance) + Overlap Length] / Line speed

 

4 Aspect = [Sighting Distance + (1.5 x Braking Distance) + Overlap Length] / Line speed.

 

For 2 Aspect, the calculation is different. You get your headway time, multiply it by the line speed. You then take away the Sighting Distance, Braking Distance and Overlap Length from this distance which gives you the distance between the two stop signals. The determination for using either two or three aspects is, as a rule of thump, is that if that distance is greater than 3 x braking distance, than 2-aspect signals is fine, otherwise 3-aspect is better.

 

Simon

Link to post
Share on other sites

  • RMweb Gold
On 13/12/2022 at 23:58, Michael Hodgson said:

The terms Home and Distant signal relates to conventional (Absolute Block) signalling practice, where signals were provided only at stations (signal boxes), signal spacing being limited by physical constraints imposed by mechanical equipment.

 

On 14/12/2022 at 18:29, St. Simon said:

As Micheal Hodgson says, the term ‘Home’ isn’t used in Multi-Aspect Signalling (unless a multi-aspect signal is used as a direct replacement for a semaphore signal), it is replaced with the term ‘Main Aspect’, but the term Distant is still is used, although it is used more in two aspect signalling, but can be seen in 3 and 4 aspect signalling as a ‘Wiltshire Distant’ as part of transitions between aspect sequences.

Ah, but, ah, but . . .

The relays used to control a three aspect signal are still abbreviations of Home Relay and Distant Relay.

 

Always intrigues/amuses me when history can be seen in modern thinking.

 

Paul.

  • Like 1
  • Informative/Useful 2
Link to post
Share on other sites

6 minutes ago, 5BarVT said:

 

Ah, but, ah, but . . .

The relays used to control a three aspect signal are still abbreviations of Home Relay and Distant Relay.

 

Always intrigues/amuses me when history can be seen in modern thinking.

 

Paul.


Lightbulb Moment Paul!

 

So, if ‘H’ is for Home (effectively a red / green), then why does it stand for ‘Yellow’ and why does ‘D’ for Distant (yellow / green), stand for ‘Green’? To me, it is more logical for H to be Green (although I’ll admit D also makes sense for Green!)?

 

Now, what about the others?

 

Simon

Link to post
Share on other sites

1 hour ago, St. Simon said:


Lightbulb Moment Paul!

 

So, if ‘H’ is for Home (effectively a red / green), then why does it stand for ‘Yellow’ and why does ‘D’ for Distant (yellow / green), stand for ‘Green’? To me, it is more logical for H to be Green (although I’ll admit D also makes sense for Green!)?

 

Now, what about the others?

 

Simon

The analogy with block signalling considers each 3 aspect signal to be a home signal and the signal in rear is its distant. If you clear just the one signal then it goes to yellow and an HR is used to do that, then should you also clear the signal in rear it needs to go to green as a distant for the first signal, hence needing a DR to set the green. You can use an HDR to do both jobs where the signal ahead clearing switches the polarity on the line wire and the HDR is a 3 position polarised relay. (And if you are using searchlight then you may be able to avoid the relays as the searchlight mechanism does the job!)  NB. Clever relay circuits to save line wires and power were much more developed in the USA when they installed all that CTC out in the sticks and using batteries and lineside pole routes where every wire and every Amp waspensive.

  • Agree 2
  • Informative/Useful 3
Link to post
Share on other sites

9 minutes ago, Grovenor said:

The analogy with block signalling considers each 3 aspect signal to be a home signal and the signal in rear is its distant. If you clear just the one signal then it goes to yellow and an HR is used to do that, then should you also clear the signal in rear it needs to go to green as a distant for the first signal, hence needing a DR to set the green. You can use an HDR to do both jobs where the signal ahead clearing switches the polarity on the line wire and the HDR is a 3 position polarised relay. (And if you are using searchlight then you may be able to avoid the relays as the searchlight mechanism does the job!)  NB. Clever relay circuits to save line wires and power were much more developed in the USA when they installed all that CTC out in the sticks and using batteries and lineside pole routes where every wire and every Amp waspensive.


Hi Keith,


That makes sense, I thought it must be something like that.

 

Simon

 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...