Route signalling vs. speed signalling - an oversimplification?

[Michael Hodgson]

3 minutes ago, big jim said:

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 

 

 

It can be argued that's about all the driver needs to know - it's not as though he could choose to steer towarsds the other line.  What he still does need to remember is that it's only a limit - he has to make the booked station stops no matter how fast the signalling tells him he can safely go.

[big jim]

20 minutes ago, Michael Hodgson said:

It can be argued that's about all the driver needs to know - it's not as though he could choose to steer towarsds the other line.  What he still does need to remember is that it's only a limit - he has to make the booked station stops no matter how fast the signalling tells him he can safely go.

my concern is in a complex area such as a big station where most of not all diverging routes may be the same speed if your wrong routed you won’t know until you get to the points, the screen will tell you to do say 20mph but it could be 20mph in the wrong direction, especially important if your on a freight with heavy axle weight, container or size restrictions, there may be a certain route through an area you can’t take such as containers through a platform road 

[melmerby]

Modern N. American signalling can have up to 3 heads and the maximum is all 3 with 3 lights (red/yellow/green)

This can have a bewildering number of combinations. Some aspects can also flash!

 

There's plenty of route based signalling still in existence, some of these mimic semaphore aspects.

[St. Simon]

32 minutes ago, big jim said:

my concern is in a complex area such as a big station where most of not all diverging routes may be the same speed if your wrong routed you won’t know until you get to the points, the screen will tell you to do say 20mph but it could be 20mph in the wrong direction, especially important if your on a freight with heavy axle weight, container or size restrictions, there may be a certain route through an area you can’t take such as containers through a platform road 

 

Hi Jim,

 

I think restrictions like those will have to improved when converting to E.T.C.S., however the idea about the Traffic Management element of E.R.T.M.S. is to help manage that side of things, the Traffic Management system will link to both the TOPS / TRUST / Train Allocation Systems / Crew Allocation systems etc and the signalling control systems and alerted (and possibly prevent) the signaller from setting restricted routes for certain trains.

 

The Automatic Route Setting system that is used also has all those restrictions programmed in, so should when being used prevent restricted routes from being set, assuming they are programmed into the timetable as well. I know that this doesn't necessarily help when the signallers are setting routes manually, but I know at TVSC they are using the Luminate Software to create Automatic Route Setting request for otherwise manually signalled trains (and really like using it). 

 

In theory with ETCS, the interlocking can ask the train via the RBC if a train is compliant with any restrictions (i.e. does it have a certain axle weight? Is it operating in Diesel Mode?), however, I don't know exactly how that might work with a freight train or whether it is possible in the current data language / set up

 

Simon

Edited May 18, 2023 by St. Simon

[St. Simon]

1 hour ago, big jim said:

my concern is in a complex area such as a big station where most of not all diverging routes may be the same speed if your wrong routed you won’t know until you get to the points, the screen will tell you to do say 20mph but it could be 20mph in the wrong direction, especially important if your on a freight with heavy axle weight, container or size restrictions, there may be a certain route through an area you can’t take such as containers through a platform road 

 

Hi Jim,

 

Just checked with a colleague and the answer in E.T.C.S. is to send a text message with the movement authority which displays on the DMI, in theory this could be about anything, but is reserve for safety critical things, such as axle weight and size restrictions. I assume that these text message would be short to avoid distractions 'NO CONTAINERS' or 'AXLE WEIGHT' or something like that.

 

Simon

[DY444]

2 hours ago, St. Simon said:

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? 

 

 

There are sort of two answers to that.

 

The first answer is that some European speed based systems provide route indicators to assist the driver in knowing onto which line the train is being routed.  For example SNCF signals sometimes have horizontal white dots above the main signal where one dot lit means you're taking the left-most route, 2 dots the second from the left etc.   DB signals at diverging junctions sometimes have theatre indicators with a letter that gives route information (not numbers as an illuminated number above a DB signal indicates the permissible speed) .

 

The second answer, and more relevant to your Paddington example, is that in many countries it doesn't matter which line you're going onto because reading your next signal is not that important until you are quite close to it.  This is because train protection systems like KVB in France and PZB in Germany supervise the train speed and braking curves when approaching a red.  Now this supervision can be relatively crude (especially PZB) compared with systems like ETRMS (or even the German LZB system used on higher speed lines) but nevertheless they make it pretty difficult to approach a red at high speed because you read the wrong signal so there's time for you to get your bearings.  Plus in Germany certainly, there is a tendency to be very generous with the provision of repeaters on the approach to stop signals which can also help.

Edited May 18, 2023 by DY444

[eldomtom2]

2 hours ago, DY444 said:

The first answer is that some European speed based systems provide route indicators to assist the driver in knowing onto which line the train is being routed.  For example SNCF signals sometimes have horizontal white dots above the main signal where one dot lit means you're taking the left-most route, 2 dots the second from the left etc.   DB signals at diverging junctions sometimes have theatre indicators with a letter that gives route information (not numbers as an illuminated number above a DB signal indicates the permissible speed) .

Which of course is why I made this thread - here we have signals in a speed signalling system that also provide the same info to the driver that they would in a route signalling system...

[dave55uk]

4 hours ago, DY444 said:

The second answer, and more relevant to your Paddington example, is that in many countries it doesn't matter which line you're going onto because reading your next signal is not that important until you are quite close to it.  This is because train protection systems like KVB in France and PZB in Germany supervise the train speed and braking curves when approaching a red.  Now this supervision can be relatively crude (especially PZB) compared with systems like ETRMS (or even the German LZB system used on higher speed lines) but nevertheless they make it pretty difficult to approach a red at high speed because you read the wrong signal so there's time for you to get your bearings.  Plus in Germany certainly, there is a tendency to be very generous with the provision of repeaters on the approach to stop signals which can also help.

Also, in Germany at least, generally the signalling goes - distant, starter, distant, starter * - so if a driver was to be routed onto some other line than he/she was expecting, then there would always be a distant signal 1km before the next stop signal. And, again generally, signals are always * placed above or immediately to the right of the line the train is on.

 

* - 99% of the time

[BR60103]

Canadian signals from an old rule book.  I think there have been more indications added.

 

 

 

I don't know if there is anything for showing a route.

I think the signals with heads on both sides of the post are block signals. Heads on the same side are interlocking.

For fun, a single red with an "A" sign is an absolute stop. Without the "A" it's stop and proceed.

 

 

There is at least one other system in North America, but I don't know it.

 

[St. Simon]

On 18/05/2023 at 14:27, St. Simon said:

 

Hi Jim,

 

I think restrictions like those will have to improved when converting to E.T.C.S., however the idea about the Traffic Management element of E.R.T.M.S. is to help manage that side of things, the Traffic Management system will link to both the TOPS / TRUST / Train Allocation Systems / Crew Allocation systems etc and the signalling control systems and alerted (and possibly prevent) the signaller from setting restricted routes for certain trains.

 

The Automatic Route Setting system that is used also has all those restrictions programmed in, so should when being used prevent restricted routes from being set, assuming they are programmed into the timetable as well. I know that this doesn't necessarily help when the signallers are setting routes manually, but I know at TVSC they are using the Luminate Software to create Automatic Route Setting request for otherwise manually signalled trains (and really like using it). 

 

In theory with ETCS, the interlocking can ask the train via the RBC if a train is compliant with any restrictions (i.e. does it have a certain axle weight? Is it operating in Diesel Mode?), however, I don't know exactly how that might work with a freight train or whether it is possible in the current data language / set up

 

Simon

 

On 18/05/2023 at 15:40, St. Simon said:

 

Hi Jim,

 

Just checked with a colleague and the answer in E.T.C.S. is to send a text message with the movement authority which displays on the DMI, in theory this could be about anything, but is reserve for safety critical things, such as axle weight and size restrictions. I assume that these text message would be short to avoid distractions 'NO CONTAINERS' or 'AXLE WEIGHT' or something like that.

 

Simon

 

Hi,

 

Turns out, potentially unsurprisingly, I was talking a bit of rubbish here as I hadn't done deep enough into the E.T.C.S. Subsets.

 

An E.T.C.S. Train does send all sorts of data to the R.B.C. (in Packet 11 for those that might be interesed):

 

• Cant Deficiency Category (currently 10 defined categories, but would be up to 15)
• Other Train Category (effectively Passenger or Freight)
• Length of Train 
• Maximum Train Speed
• Loading Gauge (currently 4 defined categories, but could be upto 256)
• Category of Axle Loading (currently 12 defined categories, but could be upto 127)
• Whether a train is 'Air Tight' (most used in the long european tunnels and Channel Tunnel)
• Number of Axles
• Operating Voltage (currently 6 defined categories, but could be up to 15, but the UK would only use 2 of the prefined ones 25kV 50Hz AC and 750v DC)
• Traction Mode

 

The Train Data is set up by the driver during start of mission, for multiple units, this is easy as it's all fixed. For a freight or loco-hauled passenger train, then it is a little more time-consuming as you will have to enter everything yourself. 

 

This train data is sent to the R.B.C. when the train first connects to it and is stored. When the R.B.C. communicates the Movement Authority to the train, it includes route suitability data, which is then compared by the train to it's own restrictions. If these don't match the train will cut the movement authority back to a point where the restrictions do match.

 

So, E.T.C.S. at the very least guards against safety-critical misrouting. But it doesn't guard against any performance hitting mis-routing.

 

Simon

Edited May 23, 2023 by St. Simon
It is actually the Train that compares the route restriction rather than the RBC

[5BarVT]

On 18/05/2023 at 10:32, 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). 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. 

East Croydon had a lot of alternative routes which went ‘across and back’.  I believe, just for performance during failures.  Anecdotally, that was why SR signalling cost more than (say) ER or LMR for a given area.

At the north end, the indication was just for the final platform irrespective of route.  As I understand it, ‘funny routes’ were limited to single yellow (possibly approach released too) so that the driver was not travelling faster than the turnout speeds.

Paul.

Edited May 19, 2023 by 5BarVT
Removed extra words

[melmerby]

20 hours ago, BR60103 said:

Canadian signals from an old rule book.  I think there have been more indications added.

 

 

 

I don't know if there is anything for showing a route.

I think the signals with heads on both sides of the post are block signals. Heads on the same side are interlocking.

For fun, a single red with an "A" sign is an absolute stop. Without the "A" it's stop and proceed.

 

 

There is at least one other system in North America, but I don't know it.

 

Try this for variety:

http://position-light.blogspot.com/2016/08/better-know-signaling-system-bnsf.html

[eldomtom2]

12 hours ago, melmerby said:

Try this for variety:

http://position-light.blogspot.com/2016/08/better-know-signaling-system-bnsf.html

Thanks for the link to that blog, it's very informative and I've finally worked out what the difference is between route and speed signalling in America is. Speed signalling tells the crew what speed to take over a diverging route, route signalling merely tells the crew that they are taking a diverging route. The confusing part is that the "Approach" aspect (next signal is red) tends to apply a speed limit even in route signalling systems.

[The Stationmaster]

This is a good site for Canadian signalling.  

 

https://www.sh1.org/eisenbahn/sac.htm

 

These are Union pacific aspects

 

https://scalesignalsystems.com/Introduction.html

 

These are D&HRR aspects

 

http://position-light.blogspot.com/2014/02/better-know-signaling-system-delaware.html

[eldomtom2]

And to add a further wrinkle into the story...

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

[4069]

A semaphore distant at caution simply means "be prepared to stop at the next stop signal, or other specified place to which the distant signal applies", to quote the current Rule Book (Handbook RS521 section 3.1). A UK driver would not recognise the expression "block signal".

Edited May 28, 2023 by 4069

[phil-b259]

1 hour ago, eldomtom2 said:

And to add a further wrinkle into the story...

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

 

In very crude terms, yes, a distant signal is telling a driver to slow down - but crucially it does not tell him WHAT speed he should adopt.

 

In speed signalling a given signal aspect will give SPECIFIC SPEED information (i.e. do not exceed XX Km/H) from this point onwards  - not just a general 'slow down' (and maybe stop) at some stage) message.

 

In reality the instruction that the driver should slow down and proceed cautiously will be combined with the drivers route knowledge as well as his knowledge about the train he is actually driving and consequently will determine the speed he should be aiming for which will vary considerably from place to place and situation to situation even where the physical distant signals are identical.

 

In summary this person you were listening two is talking nonsense and rather than going round pedalling flawed information should be turning their attention to correcting their flawed understanding of signalling methods.

 

 

[The Stationmaster]

6 hours ago, eldomtom2 said:

And to add a further wrinkle into the story...

I have heard it claimed (by someone who claims to know what they're talking about) that UK semaphore distants are speed signals, because 1) they cover multiple stop signals, any one of which being at stop places the distant at caution, and 2) a distant may be at caution even if no stop signals are at stop, e.g. when a train is being routed to a slower diverging route. Thus the argument is that a UK distant is not a block signal and conveys no information to the driver besides "slow down". Is there any truth to this argument?

Basically all it tells him is that the next stop sufgnalk in advance is at danger and he should reduce speed ready to stop at that signal.  

 

The speed at which his train is travelling is down entirely to a combination of the permitted line speed and the maximum pemitted speed for any particular train - which can be anything between 45mph and 100mph.   So there is no speed element involved at all. The requirement is that the Driver should reduce speed and be ready to come to a halt at the next stop signal (or as already referenced in the first response such other thing as the distant signal might refer to).

 

Now just to be awkward on the GWR a distant signal at caution could also indicate to a Driver that the was a restriction of speed between the rearmost and most advanced stop signals that distant related to at the next signal box.  And in one particular situation -  which applied in numerous places - the distant signal at caution indicated that speed was not to exceed 10 mph between those stop signals.

 

The term 'block signal' as such isn't used in British signalling practice.  There are two reasons for that - firstly it is irrelevant.  And secondly if any stop signals are to be referred as 'block' they would be the Outermost Home Signal  - which marks the end of a block section (in most situations as it;s a bit different on single lines) and the most Advanced Starting Signal (nowadays referred to to but not named as the Section Signal - which marks the entrance to a block section.  But as these are also stop signals just likel any other stop signal  calling them something like 'a block signal' could get confusing and lose their most important function of being a stop signal.  And of course we refer to 'block sections' - not 'blocks' (a block being something else entirely in UK operating speak as it means a line or route is blocked to the passage of trains for whatever readson).

[bécasse]

The only information that a distant signal conveys to a driver is:

 

when ON, one or more of the related stop signals may be ON and the driver should be prepared to bring the train to a stand at any of them and especially the next one. (Fixed distants obviously provide no information beyond the fact that the train is approaching a signalled area, and historically there were provisions in the rule book requiring stop signals to only be cleared progressively if the section ahead wasn't clear so if a worked distant was ON so would be the next stop signal.)

 

when OFF, none of the related signals, whether stop or running shunts, will be ON and the section ahead will be clear so the train may proceed at the maximum speed permitted for the line and/or train subject to making any booked station stops. (The driver still needs to observe the stop signals, and if possible the running shunts, in case any have been replaced to ON following an emergency.)

[Suzie]

I think that the simple differentiation is that in speed signalling the aspect tells you definitively what the maximum speed is after the signal, whereas in route signalling the aspect gives you a reference to your route knowledge/appendix to find out what speed you should be going.

 

A lot of subtle speed information can be gained from route signalling, as in the UK where the angle of the feathers tend to indicate slower routes the further the feather angle deviates from the upright, but you still need to know what the indication means - it is not an absolute speed indication - but does refer to some documentation which will tell you the speed for that particular location.

 

Some North American systems like Union Pacific where companies have been amalgamated have both route and speed aspects.

[The Stationmaster]

4 hours ago, Suzie said:

I think that the simple differentiation is that in speed signalling the aspect tells you definitively what the maximum speed is after the signal, whereas in route signalling the aspect gives you a reference to your route knowledge/appendix to find out what speed you should be going.

 

A lot of subtle speed information can be gained from route signalling, as in the UK where the angle of the feathers tend to indicate slower routes the further the feather angle deviates from the upright, but you still need to know what the indication means - it is not an absolute speed indication - but does refer to some documentation which will tell you the speed for that particular location.

 

Some North American systems like Union Pacific where companies have been amalgamated have both route and speed aspects.

The angle of the Junction Indicators ('feathers') is a geographical indication of the relative positions of the routes they read to - not an indication of variation, if any, on the turnout speed to those routes.

 

As a simple example there have been, and probably still are, signals with Position 1 (top left) and Position 4 (top right) JIs  with completely different (and on some cases widely different) speeds through the relevant diverging pointwork.

[The Stationmaster]

15 hours ago, bécasse said:

The only information that a distant signal conveys to a driver is:

 

when ON, one or more of the related stop signals may be ON and the driver should be prepared to bring the train to a stand at any of them and especially the next one. (Fixed distants obviously provide no information beyond the fact that the train is approaching a signalled area, and historically there were provisions in the rule book requiring stop signals to only be cleared progressively if the section ahead wasn't clear so if a worked distant was ON so would be the next stop signal.)

 

when OFF, none of the related signals, whether stop or running shunts, will be ON and the section ahead will be clear so the train may proceed at the maximum speed permitted for the line and/or train subject to making any booked station stops. (The driver still needs to observe the stop signals, and if possible the running shunts, in case any have been replaced to ON following an emergency.)

Alas you are somewhat adrift with the meaning of a distant signal at Caution.  Its meaning to a Driver has already been explained above and that has been its meeting in the Rules for well over a century or more.   It means that the Driver must be prepared to bring his train to a stand at the Home Signal (or any other rearmost stop signal to which that distant signal applies).  

 

The position of other stop signals applying to that line at that signal box is not always relevant.  And in any case if any one of them has to be maintained at danger the Home, or rearmost stop signal, has to be maintained at danger because of what used to be Rule 39 (but has progressed through various numbers since).  So irrespective of what other stop signals are doing, and some might even be 'off' for another train, the important thing is the need to be ready to find the rearmost one at danger and be able to stop at it.

 

The other stop signals to which that distant applies only become relevant when the distant is clear because it then indicates that all those stop signals are clear.  Subtle difference between the two situations - distant at caution reflects the situation with the first stop signal only.  Distant at clear reflects the situation in respect of all stop signals to which it applies.

[jim.snowdon]

17 hours ago, The Stationmaster said:

Basically all it tells him is that the next stop sufgnalk in advance is at danger and he should reduce speed ready to stop at that signal.  

 

The speed at which his train is travelling is down entirely to a combination of the permitted line speed and the maximum pemitted speed for any particular train - which can be anything between 45mph and 100mph.   So there is no speed element involved at all. The requirement is that the Driver should reduce speed and be ready to come to a halt at the next stop signal (or as already referenced in the first response such other thing as the distant signal might refer to).

 

Now just to be awkward on the GWR a distant signal at caution could also indicate to a Driver that the was a restriction of speed between the rearmost and most advanced stop signals that distant related to at the next signal box.  And in one particular situation -  which applied in numerous places - the distant signal at caution indicated that speed was not to exceed 10 mph between those stop signals.

 

The term 'block signal' as such isn't used in British signalling practice.  There are two reasons for that - firstly it is irrelevant.  And secondly if any stop signals are to be referred as 'block' they would be the Outermost Home Signal  - which marks the end of a block section (in most situations as it;s a bit different on single lines) and the most Advanced Starting Signal (nowadays referred to to but not named as the Section Signal - which marks the entrance to a block section.  But as these are also stop signals just likel any other stop signal  calling them something like 'a block signal' could get confusing and lose their most important function of being a stop signal.  And of course we refer to 'block sections' - not 'blocks' (a block being something else entirely in UK operating speak as it means a line or route is blocked to the passage of trains for whatever readson).

As I understand it, all that a distant signal tells the driver is that, if On, one or more of the stop signals on the line of route  within that signal box’s are of control has to be presumed to be showing a stop aspect. It doesn’t tell the driver which one, so it must always be presumed that it is the next stop signal. If it isn’t that one, it must be the next one, and so on until the driver reaches the section signal. Between those first and last signals, the driver is proceeding under line of sight. 
The only other certainty with a distant signal is that if it was Off, then all of the stop signals in the line of route were also clear.
 

I’d agree with you as regards ‘block signals’ (or the nonexistence of them in UK civilian practice), but to be fair, the space between signal boxes is termed the block section. From what I can remember, the British Army did refer to block signals / block posts on their military railways.

[big jim]

As far as I’m concerned if a distant signal is ‘on’ (at caution) the first stop signal WILL be at danger so I’ll slow down to stop at it, once I get visual confirmation of what aspect it’s showing I will either stop at it if it’s on or proceed if it’s off however I’d have to then approach all other stop signals at caution as I should expect them to be on

 

uttoxeter is a good example with a distant and 4 associated stop signals, it’s quite possible to pass the distant signal at caution, have the first 3 stop signals off and the section on, only had it happen a couple of times when the passenger train in front hadn’t reached the next box to clear the block for whatever reason  
 

 

[Michael Hodgson]

4 hours ago, jim.snowdon said:

As I understand it, all that a distant signal tells the driver is that, if On, one or more of the stop signals on the line of route  within that signal box’s are of control has to be presumed to be showing a stop aspect. It doesn’t tell the driver which one, so it must always be presumed that it is the next stop signal. If it isn’t that one, it must be the next one, and so on until the driver reaches the section signal.

No.  As explained by Stationmaster above, Rule 39(a) or its modern equivalent apply.  If a stop signal other than the first is on, not only will the distant be at caution but the train should encounter the first stop signal and any other intervening signals are also also at Danger and may only be cleared one at a time when the train has reduced speed and is demonstrated clearly to be under control for the one at which it must be stopped. 

 

If the first stop signal is off when he sights it, the driver may reasonably infer that in the period after passing the distant at caution, all the stop signals have now been taken off and that he can safely regain his speed.  This is a pragmatic way (especially in steam days) of dealing with the problem of sometimes failing to see the distant because of steam swirling round the boiler etc.