Speed signalling in GB

[12LDA28C]

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".

I was specifically referring to the UK, as that is what this thread is about, after all. Where in the UK does "XX aspect impose a speed limit of XX mph on all trains"?

 

[GC class B1]

I am interested in understanding how one set speed at an individual signal can apply to high speed passenger, local passenger and freight when each has different braking characteristics.

 

[bahnause]

I am interested in understanding how one set speed at an individual signal can apply to high speed passenger, local passenger and freight when each has different braking characteristics.

Graduated line speeds are used according to the braking ability of the different trains. A line speed can therefore be lower than a signalled speed. For switzerland, it looks like this. The braking ability is marked in yellow.

 

[GC class B1]

Graduated line speeds are used according to the braking ability of the different trains. A line speed can therefore be lower than a signalled speed. For switzerland, it looks like this. The braking ability is marked in yellow.

View attachment 141787

Thank you. Is my understanding correct that the signal shows a maximum line speed but the driver must limit the speed according to the type of rolling stock. In that case the speed signal would show the maximum line speed after that signal but this would not apply to all rolling stock types.
I think this is similar to Britain where the driver must have route and traction knowledge to interpret the meaning of the signal in terms of the speed to be passing the signal.
Another question how does the driver know whether to brake to stop at a subsequent signal.

 

[bahnause]

Thank you. Is my understanding correct that the signal shows a maximum line speed but the driver must limit the speed according to the type of rolling stock. In that case the speed signal would show the maximum line speed after that signal but this would not apply to all rolling stock types.
I think this is similar to Britain where the driver must have route and traction knowledge to interpret the meaning of the signal in terms of the speed to be passing the signal.
Another question how does the driver know whether to brake to stop at a subsequent signal.

No, the signal for line speed is a single green without any further (speed) information. This basically tells the driver to look into the route table to look up the line speed for his train. Route knowledge is not striclty required, you are allowed to drive a route without route knowledge under certain circumstances. All the information is to be found in the route table or will be given by lineside signals.

It is however possible for a signal at a junction or in a station to show for example "120km/h" to go over a set of points, but the permitted speed for a train with low braking force is only 100km/h. In this case the lower speed has to be used.

In the following video between 03:15 and 10:35 you can see a track with signal distances that are shorter than the braking distance. The train is signalled a lower speed than permitted (permitted would be 80km/h), or the "V" under the signal indicates that the next but one signal shows stop.

At 03:49 you can even see the signal for entering an occupied track.

Railway Emotions

 

[GC class B1]

Thank you to all those who had added to my limited knowledge of signalling. I now understand, as I thought, that the LMS Mirfield signalling was not speed signalling but a version of todays signalling with a larger number of options for restrictive aspects and that there has never been any true speed signalling schemes in Britain with the possible exception of ATP.
The posts have also confirmed my view that true speed signalling can only come with a system like ETCS or TVM430 and not stand alone lineside signals.

 

[eldomtom2]

Where in the UK does "XX aspect impose a speed limit of XX mph on all trains"?

...I never said there was anywhere in the UK that had such signalling.

that the LMS Mirfield signalling was not speed signalling but a version of todays signalling with a larger number of options for restrictive aspects

I don't think you've really understood how the Mirfield signalling worked.

 

[Re 4/4]

Thank you. Is my understanding correct that the signal shows a maximum line speed but the driver must limit the speed according to the type of rolling stock. In that case the speed signal would show the maximum line speed after that signal but this would not apply to all rolling stock types.
I think this is similar to Britain where the driver must have route and traction knowledge to interpret the meaning of the signal in terms of the speed to be passing the signal.
Another question how does the driver know whether to brake to stop at a subsequent signal.

Bahnause already answered this, but just to clarify:

1. yes, if the signal is "yellow 12(0)" and your train is only allowed 100 in the first place, you just continue at 100. The train going 160 obviously starts braking.

2. On lines where the signal distance is enough for the worst braking allowed train to stop from one signal to the next, you get a single yellow like in UK 3 aspect signalling at the signal before the red.

If signals are closer together, you get yellow with a V in the box, which a bit like UK double yellow in 4 aspect territory means the red is braking distance ahead (for the worst allowed train) from here, but there is at least one signal in between showing single yellow.

In no case is the approach to a red shown with speed limits, you always get a yellow without a number - but possibly with V - at braking distance.

 

[AlexNL]

To chime in on what was said about speed signalling in the Netherlands: if you're a train driver around here and you encounter a signal which is displaying a steady yellow aspect without a number, this means reduce speed to 40 km/h and expect the next signal to be at danger.

If a number is displayed alongside the yellow aspect, the next signal will be displaying a proceed aspect. But you'll have to reduce your speed to the number indicated ×10.

 

[Railsigns]

Slightly OT, but would I be correct in thinking that the first LNER five lamp 'feathers' were actually installed at Northallerton?

Probably not, because there were already some in use at Thirsk by May 1938, and Northallerton wasn't resignalled until September 1939.

 

[Annetts key]

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.

This ^

As said before, no Network Rail conventional signalling systems (lights on posts) are speed signalling systems. All ‘section’ and distant (*see notes) signals only shown information for the limit of authority of the movement. Junction signals or signals on approach to a junction signal may also provide route information (for example, flashing yellow aspects, splitting banner signals). It is the route information along with the drivers route knowledge that the driver uses to control the speed of the train to safely travel over the points and track that comprises the junction.

No signal aspect or indicator conveys any particular speed. Because different trains have different allowable speeds and different braking curves.

* some signals are not section signals, they may not be part of the aspect sequence (although they may act as a ‘distant’ for a section signal). Examples are signals provided or retained for use in an emergency, such as for protection of level crossings, tunnels or other hazards. Such signals normally only show proceed aspects and only go to red when a signaller operates a switch/control or an emergency system has been operated. Or may be unlit until operated.

TPWS is not a speed signalling system - it’s a safety system (a train protection system) which provides additional protection against a train driver not obeying a signal at red/danger, not travelling slowly enough on approach to a signal at red/danger, not travelling slowly enough on approach to a position light aspect/calling on/shunting signal (cleared or at red/danger) or on approach/at a speed restriction. In none of these cases is the speed continuously monitored. The on train equipment only checks the speed as the train passes over the second of the pair of TPWS ‘loops’ (a single ‘spot check’). The TPWS system provides absolutely no information to the driver until after it’s activated, and at that point the brake demand has already occurred.

GWML ATP is also, strictly speaking, not a speed signalling system as such. It’s a train protection system based on the existing signalling system (a limit of authority system) that supervises the train. It’s an optional safety critical system. It does however enforce all speed limits, be it the train formation maximum speed, the permitted line speed, permanent speed restrictions, temporary speed restrictions or junction speed restrictions (plus emergency speed restrictions once the S&T have been able to update the ATP equipment on site). As it provides target speed information to the driver, it could be argued that it’s close to being a hybrid speed signalling system.

ERTMS/ETCS is an in cab system and as such is a hybrid in that it can provide both route and speed signalling information, and has more functionality than the GWML ATP described above.

 

[eldomtom2]

No signal aspect or indicator conveys any particular speed. Because different trains have different allowable speeds and different braking curves.

I think you will find that rail networks that use speed signalling also deal with trains that have different allowable speeds and different braking curves.

 

[Annetts key]

I think you will find that rail networks that use speed signalling also deal with trains that have different allowable speeds and different braking curves.

Yes, of course other systems have to deal with trains that have different allowable speeds and different braking curves.

 

[Taunton]

Of course, with ATO speed signalling becomes the standard; the Victoria Line had I think just about four speeds when opened. Likewise there is no need for routing information as that just gets rolled up into the speed of approach.

If not done effectively this can lead to a considerable nuisance in the train, as it hunts around the target speed. The Jubilee Line Extension seems to have been periodically afflicted by this, through various software modifications, and backing these out later. Train gets to target 62mph, goes 1 mph over, power goes off, drops to 1mph under, power goes on, etc, sometimes leading to a lurching at each change as power is just either on, or off, and on occasion even brief brake-power-brake-power cycling, with an inability to just coast. It is strange that these inconsistencies get introduced, years after opening, and then take a while to get fixed. There was certainly more than one iteration of all this.

 

[Annetts key]

Train gets to target 62mph, goes 1 mph over, power goes off, drops to 1mph under, power goes on, etc, sometimes leading to a lurching at each change as power is just either on, or off, and on occasion even brief brake-power-brake-power cycling, with an inability to just coast.

Obviously the manufacturer or the organisation setting the parameters doesn’t understand or want to use fuzzy logic then. Fuzzy logic is supposed to ‘smooth out’ repetitive step change hunting.

 

[MarkyT]

Obviously the manufacturer or the organisation setting the parameters doesn’t understand or want to use fuzzy logic then. Fuzzy logic is supposed to ‘smooth out’ repetitive step change hunting.

Ideally, you want to ease off the power or retardation gradually as you approach a target speed, then monitor actual speed and gradually reintroduce it a little if required again. ATO systems' knowledge of upcoming gradient profiles etc would probably be useful in judging this. ISTR the hard switching at the target speed can be a feature of 'performance mode' in some ATOs compared to softer control in 'eco mode'.

 

[Taunton]

I do recall the Victoria Line, in 1967, had coasting settings, as was common then on traditional electric lines, for an early article describing it stated how, where a train was being delayed a bit at each station by a sticking door, the central controller instructed it to cut out the coasting settings, to regain time on each section. Somehow that concept seemed to be lost by the time the Jubilee Extension came along 40 years later.

 

[Goldfish62]

I do recall the Victoria Line, in 1967, had coasting settings, as was common then on traditional electric lines, for an early article describing it stated how, where a train was being delayed a bit at each station by a sticking door, the central controller instructed it to cut out the coasting settings, to regain time on each section. Somehow that concept seemed to be lost by the time the Jubilee Extension came along 40 years later.

Current ATO does the job automatically. If trains need to drive more aggressively due to a prior delay this will happen automatically.

Not sure if this is the case on all lines though. The Central line just seems to have aggressive acceleration and braking all the time.

 

[Tim M]

Current ATO does the job automatically. If trains need to drive more aggressively due to a prior delay this will happen automatically.

Not sure if this is the case on all lines though. The Central line just seems to have aggressive acceleration and braking all the time.

The Central Line ATP/ATO is based on the system developed in the early/mid 1980’s for Singapore MRT. In Singapore there were two levels of inter station coasting, maximum coast being the default level. It was up to the Operations Control Centre supervisors to cut out coasting if required, but saving energy normally came first so changing levels was rare.

LU on the other hand didn’t want/need coasting on the Central Line so that facility wasn’t implemented, hence the ‘aggressive acceleration and braking’. The Singapore system was described as the first application of intelligent ATO, with inter station speed profiles appropriate to the track geometry and not just following what the ATP speed codes dictated.

 

[Taunton]

Wonder why LU gave up with the Central what was longstanding practice on the Victoria.