Route signalling vs. speed signalling - an oversimplification?

[eldomtom2]

It appears to me that the idea of "route signalling" and "speed signalling" as two entirely separate ways of signalling is fundamentally false, and in fact there are a broad array of differing features that could be said to place any system in one of the arbitary buckets. These include:

• Whether or not a signal warning of an upcoming stop signal due to an occupied block imposes a speed limit
• Whether or not signals at junctions inform the driver of the precise route they are taking
• Whether or not signals at junctions inform the driver when they are switched to a lower-speed route (as opposed to relying on the driver's route knowledge that the route they are being switched to is lower-speed)
• Whether or not signals at junctions inform the driver when they are switched to a different route at all
• Whether or not signals at junctions can impose a speed limitt solely for the length of the crossover

Nor is the terminology consistent between countries. What the Americans call "route signalling" we would probably call "speed signalling". And there's this very common idea that speed signalling and route signalling are identical outside of their approach to junctions, but seeing as many systems impose speed limits as an occupied block is approached...

[The Stationmaster]

It is rather complex to say the least.  For example most of the colour light signalling systems in Europe devolved from the  Germanic approach to semaphore signalling are speed signalling with an added element to take account of lower speeds at divergences.  So they aren't actually route signalling as such (i.e. there is no indication of route) but the aspects indicate a lower speed - which in most cases varies according to the speed of the diverging route.

 

British signalling effectively works the opposite way round being based on route signalling but, increasingly since the introduction of flashing yellow aspects, then the re-invention of splitting distants and the provision of preliminary route  indicators (PRIs) has included a system of giving information about speed reductions when taking a diverging route.  But it is still route signalling because it does not indicate the speed by means of a specific signal aspect (the short lived ECML flashing green aspect apart).  So it can indicate the need fpr speed reduction but it still relies on separate signage and the Drver to say what that speed is.

 

Signalling derived from the French style of signalling root does bit of both depending on the way each country working from that base has developed its colour light signalling aspects (TVM cab signalling is 100% speed based).

 

These difference between the three basic styles of signalling used in Europe help to explain the problems involved in developing a Europe wide standard cab signalling system in the shape of ERTMS.  it also means that some countries have to adopt to methodology which they haven't previously encountered. For example in the latest version of ERTMS cab displays some of it would represent to an SNCF Driver nothing more than giving him an electronic display of what he previously got from a book on the desk in front of him whereas a British Driver got a lot of it from his knowledge of the road plus lineside signage to remind him.

[St. Simon]

13 hours ago, eldomtom2 said:

It appears to me that the idea of "route signalling" and "speed signalling" as two entirely separate ways of signalling is fundamentally false, and in fact there are a broad array of differing features that could be said to place any system in one of the arbitary buckets. These include:

• Whether or not a signal warning of an upcoming stop signal due to an occupied block imposes a speed limit
• Whether or not signals at junctions inform the driver of the precise route they are taking
• Whether or not signals at junctions inform the driver when they are switched to a lower-speed route (as opposed to relying on the driver's route knowledge that the route they are being switched to is lower-speed)
• Whether or not signals at junctions inform the driver when they are switched to a different route at all
• Whether or not signals at junctions can impose a speed limitt solely for the length of the crossover

Nor is the terminology consistent between countries. What the Americans call "route signalling" we would probably call "speed signalling". And there's this very common idea that speed signalling and route signalling are identical outside of their approach to junctions, but seeing as many systems impose speed limits as an occupied block is approached...

 

Hi,

 

I think I would argue that both route and speed signalling combine elements of both methods, as they both convey routing and speed information, just one system implies the speed by indicating route and the other implies the route by indicating speed. Obviously there are differences, but fundamentally both complete the drivers information on how to control their train.

 

As far as I can tell the greater difference is more in the indication of train separation, route signalling uses different indications for train separation and route information, where as speed signalling uses the same indications. 

 

Of course, an operational difference is that speed signalling can't provide the same granularity of speeds that route signalling does (it seems that most speed signalling systems only use 2 or 3 defined speeds, although in theory something like the Swiss 'N' type system would display any multiple of 10).

 

My biggest question about speed signalling is how does a driver know which signal is next? If they aren't given route information, how do they know which line they are routed to in a very complex area so they know which signal to look at? I know this isn't really a problem with a loop line, I'm thinking more of a very complex station throat, say Zurich?

 

Simon 

 

P.S. All of the above are my thoughts as a route signalling trained person with only a small, self taught knowledge of speed signalling, so it all may be rubbish!

[big jim]

1 hour ago, St. Simon said:

 

 

 

My biggest question about speed signalling is how does a driver know which signal is next? If they aren't given route information, how do they know which line they are routed to in a very complex area so they know which signal to look at?

 

 

route knowledge!

 

I’ll be honest and say I’ve not got a clue what speed signalling or route signalling is, it’s all signals to me, I take it speed signalling is the likes of using preliminary route indicators etc and route signalling is flashing yellows and route indicators 
 

[Michael Hodgson]

3 hours ago, big jim said:

route knowledge!

 

I take it speed signalling is the likes of using preliminary route indicators etc and route signalling is flashing yellows and route indicators 
 

No.  Those are route signalling (they tell you which way you're going).  You need to regulate your speed according to whatever speed limits apply to that route, which you should know based on your route knowledge, which may well be supplemented by signs.

 

Speed signalling tells you how fast you may go over the junction - but not whether that's along the main line or taking a branch or crossover.  You don't really need route knowledge, or need to know which way the points are set - it's the signalman's job to get that right.  Interlocking would of course prevent you from being shown a high speed proceed aspect if you are routed over a low speed junction.

[big jim]

Now I’m more confused! 
 

where would I experience speed signalling in the uk, struggling to think of any junctions or places where I’d see it? 

[beast66606]

13 minutes ago, big jim said:

Now I’m more confused! 
 

where would I experience speed signalling in the uk, struggling to think of any junctions or places where I’d see it? 

 

You'd need a time machine and go to Mirfield pre Healey Mills PSB (1970)

[big jim]

6 minutes ago, beast66606 said:

 

You'd need a time machine and go to Mirfield pre Healey Mills PSB (1970)

so it’s not a current thing? 

[beast66606]

Just now, big jim said:

so it’s not a current thing? 

 

Speed signalling has never been popular in the UK, I think Mirfield was the only (mainline) installation and that's long gone so it's not something you will have seen.

 

[beast66606]

11 minutes ago, big jim said:

so it’s not a current thing? 

 

If you want to read a bit more about Mirfield, the notice for it's commissioning is on this page - click on the Midland series, 1932 link

[bécasse]

Route signalling, or at least some modern incarnations of it, tells you where you are going to and not which route you are going to take to get there.

 

The automatic route setting (ARS) at East Croydon during the era of the 1984 signalling used to play some very strange "games", for example setting up a route that diverged to the left at one crossover and the right at the next rather than following the direct route into a platform and yet the only indication that the signal gave was the number of that platform. The "excuse" apparently being that the whole area was subject to a blanket 40 mph speed restriction and that all the crossovers concerned were good for that speed.

 

Drivers apparently hated it and I have twice been on a down Brighton fast train that made a full emergency brake application when the driver noticed the point blades out of kilter with the route he thought should have been set according to the signal indication. Emergency brake applications at the approach to stations aren't a very good thing from a passenger safety point of view.

[Michael Hodgson]

20 minutes ago, beast66606 said:

 

If you want to read a bit more about Mirfield, the notice for it's commissioning is on this page - click on the Midland series, 1932 link

Also described here

 

https://signalbox.org/signals/lms-speed-signalling/

 

and here (2.123 -2.124)

 

http://www.railsigns.uk/sect2page6.html

 

There's a preserved example in a carriage shed as Oxhenhope.

[big jim]

4 minutes ago, Michael Hodgson said:

Also described here

 

https://signalbox.org/signals/lms-speed-signalling/

 

and here (2.123 -2.124)

 

http://www.railsigns.uk/sect2page6.html

 

There's a preserved example in a carriage shed as Oxhenhope.

you learn something everyday! 

[Grovenor]

Should you want to learn about current speed signalling, as opposed to an historical experiment, then it is essentially the North American standard and Google will find you all you want to know and more.

Be warned, it takes a bit of effort to get your head around it, and there are a lot of minor variations used on different railroads that can make it tricky to work out what the asic system is.

[eldomtom2]

46 minutes ago, Grovenor said:

Should you want to learn about current speed signalling, as opposed to an historical experiment, then it is essentially the North American standard and Google will find you all you want to know and more.

Though of course, as I mentioned, what is called "speed signalling" outside America may be very different.

Nor can I work out what the difference between American route signalling and American speed signalling is...

[phil-b259]

1 hour ago, bécasse said:

Route signalling, or at least some modern incarnations of it, tells you where you are going to and not which route you are going to take to get there.

 

The automatic route setting (ARS) at East Croydon during the era of the 1984 signalling used to play some very strange "games", for example setting up a route that diverged to the left at one crossover and the right at the next rather than following the direct route into a platform and yet the only indication that the signal gave was the number of that platform. The "excuse" apparently being that the whole area was subject to a blanket 40 mph speed restriction and that all the crossovers concerned were good for that speed.

 

Drivers apparently hated it and I have twice been on a down Brighton fast train that made a full emergency brake application when the driver noticed the point blades out of kilter with the route he thought should have been set according to the signal indication. Emergency brake applications at the approach to stations aren't a very good thing from a passenger safety point of view.

 

East Croydon has NEVER HAD ARS!

 

I know that because I spent around 20 years in the S&T which looked after Three Bridges ASC 

 

There was an experimental ARS system designed by BR research at Derby (named George) installed to cover the Haywards Heath area put in during the mid 1980s resignalling work* but it wasn't all that reliable and was out of use by the 1990s. Even now there is no ARS at TBASC  - all routes are manually set (apart from when signals are placed in automatic mode where several trains will be using the same route one after another)

 

As such the 'games' you are talking about would be down to the way signallers set routes plus what the S&T engineers had hard wired into the interlocking.

 

* which centralised control of the Brighton line south of Norbury / Anerley to the coast in a new NX Panel box (then 8 panels, now 10) at Three Bridges

[bécasse]

11 hours ago, phil-b259 said:

 

East Croydon has NEVER HAD ARS!

 

I know that because I spent around 20 years in the S&T which looked after Three Bridges ASC 

 

There was an experimental ARS system designed by BR research at Derby (named George) installed to cover the Haywards Heath area put in during the mid 1980s resignalling work* but it wasn't all that reliable and was out of use by the 1990s. Even now there is no ARS at TBASC  - all routes are manually set (apart from when signals are placed in automatic mode where several trains will be using the same route one after another)

 

As such the 'games' you are talking about would be down to the way signallers set routes plus what the S&T engineers had hard wired into the interlocking.

 

* which centralised control of the Brighton line south of Norbury / Anerley to the coast in a new NX Panel box (then 8 panels, now 10) at Three Bridges

Interesting, I obviously remember the Haywards Heath ARS well - and some of its idiosyncrasies! - so assumed that what I had experienced on two separate occasions at East Croydon had to be the result of ARS as I assumed that no bobby would have deliberately set up such a route. The route in question being down fast to platform 3 (a straight run) but actually routed left (as if towards platform 4) and then immediately right (back towards platform 3). A dozen years on I can't remember whether the relevant signal had a theatre light indicator or feathers (I rather presume that with a 40 mph restriction it was the former) but, either way, the indication would have been the same - platform 3 as the destination.

 

The second time that it happened to me I had a quick word with the driver on arrival at Brighton and he suggested that it certainly wasn't the first time that it had happened to him there. I can't really imagine a bobby deliberately setting up such a route unless there was a failure, so I wonder if a preceding service had been routed down fast to 5 or 6 (requiring the first crossover to be reversed) and the S&T algorithms then caused the second crossover to reverse for the passage of the Brighton train rather than normalising the first one. 

[Michael Hodgson]

25 minutes ago, bécasse said:

Interesting, I obviously remember the Haywards Heath ARS well - and some of its idiosyncrasies! - so assumed that what I had experienced on two separate occasions at East Croydon had to be the result of ARS as I assumed that no bobby would have deliberately set up such a route. The route in question being down fast to platform 3 (a straight run) but actually routed left (as if towards platform 4) and then immediately right (back towards platform 3).

 

There are always reasons why a signalman might route  a train via what would normally be a sub-optimal route. 

For example a broken rail on the main line in the case you describe.

[The Stationmaster]

15 hours ago, big jim said:

you learn something everyday! 

Jim what indications do you get on the cab displays with ERTMS ?

[Edwin_m]

In situations where there are multiple possible routes between two signals, there may be some means for the signaller to select one rather than another, such as an intermediate button or keying a point, or the non-preferred route being selected automatically if the preferred one is not available.  But this will only be provided if there is some operational benefit, for example crossing over and back if another train is signalled over the piece of track that makes up the more obvious straight route between the crossovers.  

 

Getting back to the topic, how (if at all) does speed signalling protect against hazards such as an electric train being sent down a non-electrified line, or a train being routed towards a line where clearances or axle load aren't sufficient?  In British practice the driver should be make aware this is going to happen in time to stop at the junction or at least beyond the junction but before any hazard can arise.  

[The Stationmaster]

22 hours ago, St. Simon said:

 

 

My biggest question about speed signalling is how does a driver know which signal is next? If they aren't given route information, how do they know which line they are routed to in a very complex area so they know which signal to look at? I know this isn't really a problem with a loop line, I'm thinking more of a very complex station throat, say Zurich?

 

Simon 

 

Simon you culd also ask onroute signalling how does a Drib ver lknow where the next signal is?   The Driver knows from signals the route which the train will take but the only way he knows where the next signal is sited is from route knowledge.

 

Zurich Hbf answers your question very easily as it happens because on the surface lines it is a terminus and - as far as I  can recall - the stop blocks line up.   A better example would probably be somewhere like Basle where the platform ends don't align.  And here we come to a fundamental difference between Britain and the mainland European Railways., and that is the matter of line capacity.

 

To take a simple example know to some of us if Crossrail had been built to continental standards it would pt robably have justified two additional running lines for at least part of the distance out to Shenfield and it would all too obviously have justified two additional running lines from Westbourne Park to Maidenhead.  that is what would have happened in just about any mainland European country you care t name because the railway (infrastructure owber nowadays) would have useda set of UIC standard calculations based on UIC Fiche 406 and said to those who wanted the extra services this is the capacity increase that will mean and the Govt will have to pay for it.   An example that often used to quoted was Fratton to Portsmouth Harbour where applying the UIC calculations would have meant quadruple track throughout.

 

In Britain we've generally been happy since WWII to try to muddle along squeezing quarts into pint pots and congratulating ourselves on being able to create and operate such railways - until something goes wrong.   'Over there' what they do is add extra running lines and enlarge stations to handle extra flows and that also means services can reasonably reliably always use the same, or the same group of, platforms.  It costs more (very un-British to spend money on such things  - until the excrement has well and truly interfaced with the fan and no other choice exists) but delays are fewer, timetable planning is simpler, and it works more smoothly all the time (things like unexploded WWII bombs and other unusual things apart).

 

Signalling is also highly standardised unlike Britain where, as a  good example, various details of colour light signalling practice varied between BR Regions as late as the 197os and a nationally standard range of all components didn't really exist until the 1990s.  In Germany for example the distance between a Vorsignal (= UK distant signal) is standardised across the entire network varying only according to line speed - and that has been the case since DR was first created.  Again BR Regional semaphore practice remained in place for over 4 decades after nationalisation.  Coupled with other working practice differences it means - taking France as the best example - that a Driver can learn several hundred miles of 'new' (to them) route in less than week with no need even for a route learning videos etc.  And SNCF's SPAD rate is usually in single figures for the whole country per annum.

 

So lots of differences from the way we do things and a lot of it is down to teh simplicity created by having a lot more railway on which to run trains.  so less need to worry about electric trans running onto non electrified lines but even that can be dealt with (as on CTRL) through various design mitigations.

 

 

[St. Simon]

41 minutes ago, The Stationmaster said:

Simon you culd also ask onroute signalling how does a Drib ver lknow where the next signal is?   The Driver knows from signals the route which the train will take but the only way he knows where the next signal is sited is from route knowledge.

 

Hi Mike,

 

I was thinking more of the situation such as leaving Paddington (where all lines are bi-directional and all signals are on parallel gantries) on Line 6 and you are routed to Line 3, but as the whole junction has the same speed a speed signalling system will (I assume) show the same indication regardless of what line you are routed on to.

 

In this situation, how does the driver know which line they are routed on to? 

 

I can understand that route knowledge is fundamental to it, but in this sort of scenario, I haven't seen enough enough to understand it.

 

1 hour ago, The Stationmaster said:

Jim what indications do you get on the cab displays with ERTMS ?

 

E.T.C.S. displays speed, no routing information is provided.

 

1 hour ago, Edwin_m said:

Getting back to the topic, how (if at all) does speed signalling protect against hazards such as an electric train being sent down a non-electrified line, or a train being routed towards a line where clearances or axle load aren't sufficient?  In British practice the driver should be make aware this is going to happen in time to stop at the junction or at least beyond the junction but before any hazard can arise.  

 

I'm not sure about 'conventional' speed signalling systems (although I believe that some places may have 'interlocking' between electrification and signalling systems), but E.T.C.S. provides in-cab indications  to provide the driver with information on things ahead and in theory you could 'interlock' the signalling against information provided by the train itself.

 

Of course, if 'pre-warning' indications are not provided, the signalling layout can be configured (if possible) that the point at which the driver is certain something is wrong is at least braking distance from the hazard, to mitigate a safety risk.

 

I'm beginning to think I need to start a new thread about the actual workings of E.T.C.S.....

 

Simon

[St. Simon]

2 hours ago, Michael Hodgson said:

 

There are always reasons why a signalman might route  a train via what would normally be a sub-optimal route. 

 

I know in the case of a few signallers, they do it because they can!

 

17 hours ago, bécasse said:

Route signalling, or at least some modern incarnations of it, tells you where you are going to and not which route you are going to take to get there.

 

Not necessarily, we now try to provide separate indications for all alternative routes (unless you are somewhere like Cardiff Central which has 32 routes off one signal, most being alternative routes) to provide full clarity to the driver, as now most alternative routes are sufficiently different such that they are really different routes.

 

Simon

[big jim]

1 minute ago, St. Simon said:

 

 

E.T.C.S. displays speed, no routing information is provided.

 

 

 

As mentioned in the ERTMS thread you can work out if you are taking a slower diverging route ahead by looking at the size of the open planning area, ie at a station you can tell if your diverging at 15mph or going straight on at 40mph at the points, but that’s about it 

 

 

[Michael Hodgson]

1 minute ago, St. Simon said:

 

I know in the case of a few signallers, they do it because they can!

 

Many signalmen had a better understanding of the benefits of operational flexibility than some of their penny-pincing managers.  I've heard of trains being routed via little-used goods loops just to polish the rails when they knew an inspection was imminent - in an era when any track with rusty rails was a prime candidate for lifting.