Speed signalling in GB

[12LDA28C]

If there's a specific speed listed in the rules that drivers must always be under when passing all single yellow signals, I would call that progressive speed signalling.

It's company-specific instructions which would mean that one TOC would instruct its drivers to pass a particular signal at one speed and another TOC would instruct its drivers to pass the same signal at a different speed. So the signal or signalling system itself does not dictate the speed.

 

[eldomtom2]

Speed signalling is where the signalling system conveys authority to the driver to proceed at a specified speed. Progressive Speed signalling sounds like another name for just 'driving properly'. The only 'true' speed signalling system in the UK is TVM-430. All other signalling systems indicate whether or not a track ahead is occupied and the driver is expected to modify their speed accordingly, but the signalling itself does not change the authority to move at a specified speed.

Are you defining speed signalling to solely include cab signalling systems? Progressive speed signalling is entirely about "conveying authority to the driver to proceed at a specified speed" - that's what makes it different from speed signalling at junctions, which only dictate speed over junctions and not outside of them.

It's company-specific instructions which would mean that one TOC would instruct its drivers to pass a particular signal at one speed and another TOC would instruct its drivers to pass the same signal at a different speed. So the signal or signalling system itself does not dictate the speed.

How can a signal dictate speed outside systems like TPWS?

 

[ac6000cw]

These are the definitions I personally use:
Route signalling - signals at junctions indicate which route the train is being routed on
Speed signalling - signals at junctions indicate the speed limit for the upcoming junction
Progressive speed signalling - signals warning of an upcoming stop signal impose speed limits on trains passing them

So which category would you put the (USA) Southern Railway signalling system in post #16 in? (as it's basically simple speed signalling but with divergence indications, so has a element of route signalling especially since at many junctions there's only one alternative route).

 

[12LDA28C]

Are you defining speed signalling to solely include cab signalling systems? Progressive speed signalling is entirely about "conveying authority to the driver to proceed at a specified speed" - that's what makes it different from speed signalling at junctions, which only dictate speed over junctions and not outside of them.

How can a signal dictate speed outside systems like TPWS?

Its aspect can. For example some TOCs require drivers to have reduced speed to no more than 50% of line speed in 4-aspect signalling areas by the time they reach the single yellow, known as the '50% Rule'.

 

[zwk500]

Are you defining speed signalling to solely include cab signalling systems?

Not at all, see this indication authorising 80kph:

(This is NS in the Netherlands, a single yellow there means strictly 40kph, unless the display indicates a different speed - as it does here. The image is a still from a cabride video on youtube).

Progressive speed signalling is entirely about "conveying authority to the driver to proceed at a specified speed" - that's what makes it different from speed signalling at junctions, which only dictate speed over junctions and not outside of them.

I have never heard anybody talk about progressive speed signalling before you. Do you have an example of a railway that uses this or is it your own definition?

 

[12LDA28C]

How can a signal dictate speed outside systems like TPWS?

You're the one quoting 'speed signalling' so you tell me?

 

[eldomtom2]

So which category would you put the (USA) Southern Railway signalling system in post #16 in? (as it's basically simple speed signalling but with divergence indications, so has a element of route signalling especially since at many junctions there's only one alternative route).

A mix of all of them, like many US systems. They are not "one-or-the-other" categories.

Its aspect can. For example some TOCs require drivers to have reduced speed to no more than 50% of line speed in 4-aspect signalling areas by the time they reach the single yellow, known as the '50% Rule'.

Yes, that was what I was getting at. I was responding to a statement that seemed to imply that aspects couldn't.

Not at all, see this indication authorising 80kph:

(This is NS in the Netherlands, a single yellow there means strictly 40kph, unless the display indicates a different speed - as it does here. The image is a still from a cabride video on youtube).

Yes, the Netherlands use progressive speed signalling. But a question for you - if there were no displays and a single yellow always meant 40kph, would that still be speed signalling in your view.

I have never heard anybody talk about progressive speed signalling before you. Do you have an example of a railway that uses this or is it your own definition?

Japan would be the classical example. I believe the term "progressive speed signalling" comes from the Netherlands, as I found it in a book on signalling written by a Dutchman. It's the only term for the system of "cautionary aspects impose speed restrictions" that I've found.

 

[zwk500]

But a question for you - if there were no displays and a single yellow always meant 40kph, would that still be speed signalling in your view.

Yes. The signal aspect gives authority to move at 40kph. This is different from non-speed signalling, where the signal aspect gives authority to move towards a specific point. AIUI the Dutch single yellow does not indicate which route is set at junctions.

Japan would be the classical example. I believe the term "progressive speed signalling" comes from the Netherlands, as I found it in a book on signalling written by a Dutchman.

Interesting. The Wikipedia article is unclear whether the Japanese signals specifically modify the authority to move at certain speeds or whether they are just guideline speeds. Would you happen to be able to recommend a better source available online?

It's the only term for the system of "cautionary aspects impose speed restrictions" that I've found.

I would make no distinction between types of speed signalling for this. Either the signalling system dictates the speeds authorised or it doesn't. Notably under the Dutch system a single Yellow aspect does not change it's meaning depending on whether it is on plain line or a junction.

 

[GC class B1]

A respected colleague of mine who is a retired driver with many years of experience has advised me that you could describe all signals in Britain as speed control signals. As an example a green signal is a movement authority that permits the driver to move at a speed that is either, the maximum line speed, the maximum speed of the rolling stock if lower than the line speed, or possibly a lower speed if the braking characteristics of the rolling stock dictate a lower speed because of the signal spacing stopping distance. A restrictive aspect instructs the driver to drive at a speed that ensures the train does not pass the limits of the movement authority. Any other speed limits would therefore need to be conveyed to the driver by another means as in the example in post number 35.
To explain further, a feather indicates the route that the train is signalled to take and this may indicate a different speed limit than other routes.

 

[12LDA28C]

A respected colleague of mine who is a retired driver with many years of experience has advised me that you could describe all signals in Britain as speed control signals. As an example a green signal is a movement authority that permits the driver to move at a speed that is either, the maximum line speed, the maximum speed of the rolling stock if lower than the line speed, or possibly a lower speed if the braking characteristics of the rolling stock dictate a lower speed because of the signal spacing stopping distance. A restrictive aspect instructs the driver to drive at a speed that ensures the train does not pass the limits of the movement authority. Any other speed limits would therefore need to be conveyed to the driver by another means as in the example in post number 35.
To explain further, a feather indicates the route that the train is signalled to take and this may indicate a different speed limit than other routes.

With respect to your colleague, I disagree with this. If a signal is a movement authority that permits the drivers of different trains to proceed at different speeds then how can that be possibly described as 'speed signalling'? If one specific speed is mandated, say 50mph then that is speed signalling.

 

[zwk500]

To explain further, a feather indicates the route that the train is signalled to take and this may indicate a different speed limit than other routes.

There are plenty of signals with feathers where all possible routes from the signal are the same speed, or where different feathers read to routes with different speeds and there is no indication to the driver which speed applies when the feather is lit.

 

[Ken H]

With respect to your colleague, I disagree with this. If a signal is a movement authority that permits the drivers of different trains to proceed at different speeds then how can that be possibly described as 'speed signalling'? If one specific speed is mandated, say 50mph then that is speed signalling.

Because each train type has a braking curve. A driver will know through his route knowledge that when driving a class 999 train, he can pass a double yellow at 70, and a single yellow at 35 AT THAT LOCATION ONLY.
But next day when driving a class 998, he may be able to pass the double yellow at 80 and the single yellow at 40 because of better braking characteristic.

 

[eldomtom2]

Yes. The signal aspect gives authority to move at 40kph. This is different from non-speed signalling, where the signal aspect gives authority to move towards a specific point. AIUI the Dutch single yellow does not indicate which route is set at junctions.

I would make no distinction between types of speed signalling for this. Either the signalling system dictates the speeds authorised or it doesn't. Notably under the Dutch system a single Yellow aspect does not change it's meaning depending on whether it is on plain line or a junction.

Well the fact of the matter is that in many places speed signalling and route signalling are viewed as a distinction that applies to junctions only, hence why the alternative to "speed signalling" is often seen as "route signalling". This is why I use the term "progressive speed signalling". However, I should note that under these systems of "speed signalling" that only impose speed limits at junctions, it is not a case of aspects meaning something different at junctions - rather, there are a whole host of junction-only aspects.

Interesting. The Wikipedia article is unclear whether the Japanese signals specifically modify the authority to move at certain speeds or whether they are just guideline speeds. Would you happen to be able to recommend a better source available online?

I thought the English Wikipedia article was very explicit that they did impose speed limits. That they impose speed limits is such a commonly known aspect of Japanese signalling practice that it's hard to find sources that don't discuss the speed limits different aspects impose.

 

[12LDA28C]

Well the fact of the matter is that in many places speed signalling and route signalling are viewed as a distinction that applies to junctions only, hence why the alternative to "speed signalling" is often seen as "route signalling". This is why I use the term "progressive speed signalling". However, I should note that under these systems of "speed signalling" that only impose speed limits at junctions, it is not a case of aspects meaning something different at junctions - rather, there are a whole host of junction-only aspects.

According to whom?

 

[eldomtom2]

According to whom?

According to the basic concept of setting speed signalling in opposition to route signalling.

 

[GC class B1]

With respect to your colleague, I disagree with this. If a signal is a movement authority that permits the drivers of different trains to proceed at different speeds then how can that be possibly described as 'speed signalling'? If one specific speed is mandated, say 50mph then that is speed signalling.

I agree that to be genuinely called speed signalling the signal would need to display the speed for each type of train. I think this can only be the case with in cab signalling such as TVM430. I think that speed signalling with line side signals is unlikely to be feasible. Lineside signals must therefore rely on drivers knowing the relevant maximum speed for the location, rolling stock and signal aspect. A lineside signal indicating the maximum speed for the track ahead would still require drivers to comply with speed restrictions because of rolling stock or other non infrastructure differences. Any discussion about speed signalling must be based on a definition of speed signalling and I am not sure what this is. I studied the information about the LMS speed signalling installation at Mirfield and this didn’t fit with my understanding of speed signalling. I expected speed signals to indicate the maximum speed at each signal. This arrangement seemed to me to just have more options for restrictive aspects than the two or three aspect signalling generally in use at the time. If I am correct then it could be argued that four or five aspect signalling is an improved speed signalling giving more information to the driver about maximum speed at each signal compared to three aspect signalling.

 

[12LDA28C]

According to the basic concept of setting speed signalling in opposition to route signalling.

Drivers drive to the signals and their route knowledge dictates their speed. Simple.

== Doublepost prevention - post automatically merged: 28 Aug 2023 ==

Because each train type has a braking curve. A driver will know through his route knowledge that when driving a class 999 train, he can pass a double yellow at 70, and a single yellow at 35 AT THAT LOCATION ONLY.
But next day when driving a class 998, he may be able to pass the double yellow at 80 and the single yellow at 40 because of better braking characteristic.

Of course. But this is not speed signalling.

 

[bahnause]

I expected speed signals to indicate the maximum speed at each signal.

It could, but in general it will show you a speed restriction or something like a single green signal for "line speed". Line speed can be the same for all trains or be dependent on rolling stock, braking capabilities etc. Line speed for a certain type of train can be lower as a restrictive signalled speed. Speed signalling can be descibed with the absence of the information about the route that will be taken.

 

[Tester]

Some basic principles may be helpful (it's a signalling thing!).

There is no fundamental distinction between route signalling and speed signalling on plain line (in simple terms - there are always exceptions).

The big difference is how diverging routes are dealt with.

In route signalling the driver is told which route is set, but not the applicable speed (the driver determines this by route knowledge).

In speed signalling the driver is told the applicable speed, but not which route is set.

There are pros and cons with each system - for example misrouting can be more problematic in speed signalling.

They both have a long pedigree and are in widespread use. Generally one tends to prefer the system one has grown up with - finding the 'other' one baffling! But they are just two ways of doing the same job.

 

[eldomtom2]

I agree that to be genuinely called speed signalling the signal would need to display the speed for each type of train. I think this can only be the case with in cab signalling such as TVM430. I think that speed signalling with line side signals is unlikely to be feasible.

A rather odd

Any discussion about speed signalling must be based on a definition of speed signalling and I am not sure what this is. I studied the information about the LMS speed signalling installation at Mirfield and this didn’t fit with my understanding of speed signalling. I expected speed signals to indicate the maximum speed at each signal. This arrangement seemed to me to just have more options for restrictive aspects than the two or three aspect signalling generally in use at the time.

The speed signalling at Mirfield was about indicating to drivers what speed they should take an upcoming junction at. When viewed from this angle how it's "speed" signalling makes sense.

Drivers drive to the signals and their route knowledge dictates their speed. Simple.

I have no idea what this is meant to prove, or how it responds to my post.

There is no fundamental distinction between route signalling and speed signalling on plain line (in simple terms - there are always exceptions).

Correction - this is the case when one talks about route vs. speed signalling at junctions. This is why I use the term "progressive speed signalling" to refer to signals enforcing speed limits on plain line.

 

[GC class B1]

Some basic principles may be helpful (it's a signalling thing!).

There is no fundamental distinction between route signalling and speed signalling on plain line (in simple terms - there are always exceptions).

The big difference is how diverging routes are dealt with.

In route signalling the driver is told which route is set, but not the applicable speed (the driver determines this by route knowledge).

In speed signalling the driver is told the applicable speed, but not which route is set.

There are pros and cons with each system - for example misrouting can be more problematic in speed signalling.

They both have a long pedigree and are in widespread use. Generally one tends to prefer the system one has grown up with - finding the 'other' one baffling! But they are just two ways of doing the same job.

Could you explain to a layman please how the speed signal tells the driver the applicable speed at the signal. Is this by displaying a numerical value to the driver rather than a colour.

 

[zwk500]

Could you explain to a layman please how the speed signal tells the driver the applicable speed at the signal. Is this by displaying a numerical value to the driver rather than a colour.

In general, yes. Although some speed signalling systems do use plain colour-light aspects to indicate specific speeds.

https://en.wikipedia.org/wiki/Belgian_railway_signalling#/media/File:CX-D.45.jpg (link to picture of Belgian Railway signal showing '5' numerical indicator for speed limit of 50kph).
https://en.wikipedia.org/wiki/Railway_signal#/media/File:Einfahrsignal_Friedrichsdorf_Hp2_Zs3v.jpg (link to German Railway signal showing '3' numerical indicator for speed limit of 30kph, overriding fixed indication of 6/60kph at signal due to being routed towards caution/obstruction.)

 

[12LDA28C]

Correction - this is the case when one talks about route vs. speed signalling at junctions. This is why I use the term "progressive speed signalling" to refer to signals enforcing speed limits on plain line.

So where and how do signals enforce speed limits on plain line? Have you ever driven a train over a route where this system is in place?

 

[Tester]

Could you explain to a layman please how the speed signal tells the driver the applicable speed at the signal. Is this by displaying a numerical value to the driver rather than a colour.

Different railways do things differently (what a surprise!).

The one I'm most familiar with (Victoria, Australia) has a default medium speed (in simple terms turnout speed) of 40km/h. This can be modified upwards (typically to 65 or 80km/h) by a numerical display. No lamp proving required - if the numerical display fails the lower limit applies.

All signal indications consist of a minimum of two aspects shown together - a single aspect is to be treated as a failure. In many cases one of the aspects is red even for proceed - for example the least restrictive aspect (the equivalent of our green) is green over red - something that takes a bit of getting used to!

As with so many things, once you're used to it it's simple and effective - until then it's quite daunting!

 

[bahnause]

So where and how do signals enforce speed limits on plain line? Have you ever driven a train over a route where this system is in place?

Yes and yes, but not in the UK…

 

[Re 4/4]

Could you explain to a layman please how the speed signal tells the driver the applicable speed at the signal. Is this by displaying a numerical value to the driver rather than a colour.

In Switzerland, the newer system uses numbers, so green + digit 6 means 60 km/h (terms and conditions apply). The older system uses colours: single green is linespeed, double green is 60 and triple green is 90. Of course, these signals have proving circuits to make sure they don't display a higher limit by accident if a bulb is out.

So where and how do signals enforce speed limits on plain line? Have you ever driven a train over a route where this system is in place?

Not a driver, but I think in Switzerland, if you have a plain line with a section with a permanent speed restriction, the newest signalling system will give you the digit in the box too.

As far as I know, you also get triple green (90) in the older system on the "home signal" (Einfahrsignal) if there's a permanent speed restriction through a station even on the straight track, on an otherwise higher-speed line. But that's not plain line, of course.

 

[bahnause]

Not a driver, but I think in Switzerland, if you have a plain line with a section with a permanent speed restriction, the newest signalling system will give you the digit in the box too.

This would be a rare case. Often, speed signalling is used on open track when the braking distance extends over several signals due to short signal distances. Another application is speed optimisation to avoid conflicts at junctions. In this case, a train is slowed down to avoid a stop at the bottleneck. This function is increasingly handled by push messages to the drivers' tablets or text messages to the GSM-R radio instead of using the signals.

 

[Taunton]

The term "speed signalling" comes from the USA, where a predecessor of the Association of American Railroads (AAR), a longstanding super-ATOC and Regulator combined, defined signal aspects long ago, bringing together the various different actual signal types. This explanation of theirs is from a 1910 signal manufacturer's catalogue.

North American railroad signals - Wikipedia

en.wikipedia.org

Note the term "normal speed". The Mirfield expression "high speed" seems to have been an LMS-ism when using this USA equipment. And there's no actual MPH value associated with it, that's still for the driver and other regulations to determine separately.

UK semaphore signalling even incorporated elements of this, where on a signal gantry signals for diverging routes were set a little lower than those for the through route, implying a slower speed.

 

[GC class B1]

So where and how do signals enforce speed limits on plain line? Have you ever driven a train over a route where this system is in

In general, yes. Although some speed signalling systems do use plain colour-light aspects to indicate specific speeds.

https://en.wikipedia.org/wiki/Belgian_railway_signalling#/media/File:CX-D.45.jpg (link to picture of Belgian Railway signal showing '5' numerical indicator for speed limit of 50kph).
https://en.wikipedia.org/wiki/Railway_signal#/media/File:Einfahrsignal_Friedrichsdorf_Hp2_Zs3v.jpg (link to German Railway signal showing '3' numerical indicator for speed limit of 30kph, overriding fixed indication of 6/60kph at signal due to being routed towards caution/obstruction.)

Thank you zwk500 for this information.

 

[eldomtom2]

So where and how do signals enforce speed limits on plain line? Have you ever driven a train over a route where this system is in place?

As I said, Japan is the obvious example. As for how, it's very simple. You just have the rules say "XX aspect imposes a speed limit of XX mph on all trains".

And there's no actual MPH value associated with it, that's still for the driver and other regulations to determine separately.

Normal US practice is to specifically define terms like "medium speed" as XX mph, not leave that for the driver to determine.

UK semaphore signalling even incorporated elements of this, where on a signal gantry signals for diverging routes were set a little lower than those for the through route, implying a slower speed.

You've got cause and effect backwards - speed signalling evolved from route signalling and its separate signals for diverging routes, not the other way around.