Digitalised signalling

[John1974]

Can someone explain to me how this works and does this mean driverless trains?

 

[Eccles1983]

Is that you Chris Grayling?

Jokes aside digital signalling means that a computer will call and set the routes, with minimal human input.

It has nothing to do with driverless trains.

 

[swt_passenger]

Can someone explain to me how this works and does this mean driverless trains?

A lot of the public utterances are basically politician’s spin. “Digital electronics” have been controlling signals for donkey’s years. What they now really mean by “digital” in this context is radio communications based signalling, eventually without trackside signalling (aka lights on sticks). This is effectively what is fitted on HS1 and some LU lines.

There’s no realistic suggestion that there’ll ever be ‘driverless’ main line trains, but some drivers may well just be monitoring their train for periods while it’s running under Automatic Train Operation (ATO). This is intended shortly for first regular use in the Thameslink central core area through London, but the driver will still start the train after each call.

 

[pdeaves]

"Digital signalling" means, to most people, ETCS and ERTMS (European train control system and European rail traffic management system), for which there is loads on the internet.

True "digital" means one state or one other state, which goes back to mechanical signalling: either the signal is on or it's off. Not many people would actually call this digital signalling, though!

 

[edwin_m]

ERTMS level 2, as implemented on the Cambrian and the core of Thameslink, retains train detection by track circuits and axle counters but transmits a "movement authority" to the train instead of using signals. So if all the trains on the route have the appropriate equipment, signals are not needed (this applies to the Cambrian but Thameslink opted to keep physical signals as a backup).

Other systems are fully transmission-based with the train reporting its position by radio too, so in principle trackside equipment to detect trains is not needed, although they may retain this equipment in more critical locations. These tend to be only on metros, although there is a future ERTMS level 3 for main line use which needs to take account of factors such as wide variation in train performance and length.

All these systems know how far the train can go under its movement authority, as well as gradients in between and how good the brakes are, so can calculate the maximum safe speed to run at. Normally the driver is free to drive at any speed below that but the system will intervene if they exceed the safe speed. However having got the basic system in place, it can be extended to let the the train drive itself at a speed below the safe speed and to include station stops.

 

[Ken H]

Surely all signalling has been digital since the first computer interlocking at Leamington Spa as opposed to the relay based stuff which came earlier?

 

[Highlandspring]

Surely all signalling has been digital since the first computer interlocking at Leamington Spa as opposed to the relay based stuff which came earlie

The first computer based interlocking was the RETB SSI at Dingwall in 1984, which predated Leamington Spa SSI by a year.

 

[Cherry_Picker]

Yeah, but you've gotta have buzz words and ''digital" is one of the railway's particular favourites.

 

[Ken H]

The first computer based interlocking was the RETB SSI at Dingwall in 1984, which predated Leamington Spa SSI by a year.

Thanks for correction. Thats one of my pearls of knowledge in the bin

 

[Ken H]

Yeah, but you've gotta have buzz words and ''digital" is one of the railway's particular favourites.

Yeah. what is a 'digital motor'? Are they not all rotating magnets and wire?

 

[Ediswan]

True "digital" means one state or one other state, which goes back to mechanical signalling: either the signal is on or it's off. Not many people would actually call this digital signalling, though!

Digital can be multi-state, it does not have to binary. What it is definitely not is continuously variable, that would be analogue. So I agree, an on/off mechanical signal is digital. So is a three or four aspect light signal.

I blame the phone system. That (as far as I recall) is where 'digital' started being used as a marketing phrase. In that case it was true. There audio transmission did change from analogue to digital (both electronic).

 

[Belperpete]

"Digital signalling" means, to most people, ETCS and ERTMS (European train control system and European rail traffic management system), for which there is loads on the internet.

Network Rail are also looking at enhanced Control Centres as part of their "digital signalling".

As Ediswan says, digital does not mean binary, although it is often used that way. "Digital" comes from "digit", i.e. something that can be counted using fingers. "Digital signalling" does just seem to be a buzz-word for modern signalling and control systems, to make Network Rail look cool and modern. Unfortunately, Railtrack didn't take a particularly active role in the early development of ETCS, regarding that as the suppliers' role, which means that in reality Network Rail now has little say on how the system works.

 

[Shaw S Hunter]

Yeah, but you've gotta have buzz words and ''digital" is one of the railway's particular favourites.

And unfortunately SoS Grayling has been utterly seduced by it without, it seems, understanding what it does, or more importantly, does not mean in railway terms.

 

[edwin_m]

Network Rail are also looking at enhanced Control Centres as part of their "digital signalling".

As Ediswan says, digital does not mean binary, although it is often used that way. "Digital" comes from "digit", i.e. something that can be counted using fingers. "Digital signalling" does just seem to be a buzz-word for modern signalling and control systems, to make Network Rail look cool and modern. Unfortunately, Railtrack didn't take a particularly active role in the early development of ETCS, regarding that as the suppliers' role, which means that in reality Network Rail now has little say on how the system works.

Arguably someone holding a red and green flag with their fingers is also "digital". Better terms for the various generations of signalling technology would be something like "mechanical", "relay-based", "computer-based" and "communications-based".

 

[carriageline]

Network Rail are also looking at enhanced Control Centres as part of their "digital signalling".

As Ediswan says, digital does not mean binary, although it is often used that way. "Digital" comes from "digit", i.e. something that can be counted using fingers. "Digital signalling" does just seem to be a buzz-word for modern signalling and control systems, to make Network Rail look cool and modern. Unfortunately, Railtrack didn't take a particularly active role in the early development of ETCS, regarding that as the suppliers' role, which means that in reality Network Rail now has little say on how the system works.

What is an “enhanced control centre” when it’s at home?

 

[Sunset route]

What is an “enhanced control centre” when it’s at home?

It’s an ROC where the mess rooms actually have doors and the staff can control their own lighting and air con lol

 

[pdeaves]

Digital can be multi-state, it does not have to binary.

Fair point, I was trying to keep it simple but obviously over-simplified!

 

[Highlandspring]

It’s an ROC where the mess rooms actually have doors and the staff can control their own lighting and air con lol

I’m dreaming about those dizzying future technological advances already.

 

[edwin_m]

where the mess rooms actually have doors

Does that mean they can keep working next time the toaster catches fire rather than stopping half the network?

 

[driver_m]

They'll be calling it HD or 4K signalling next to try and emphasis the new and shiny part of it. You'd think NR were saying their target audience were elderly old dears who still use analogue telephones .

 

[NSEFAN]

You'd think NR were saying their target audience were elderly old dears who still use analogue telephones

Now now thats not a nice way to talk about Grayling and his department. They mean well.

On the subject of in-cab signalling, the only reasons to install it are either higher speed (beyond 125mph, where it's too fast to reliably read line side colour lights) or higher capacity (allowing trains to squeeze closer together on metro routes). Give the amount of legacy infrasture on the network, I expect that fully driverless trains won't be here for some time. Resignalling is expensive, disruptive and time consuming (lots of safety checks needed), so it's probably going to be cheaper to employ drives for a while yet.

 

[Greg Read]

It’s an ROC where the mess rooms actually have doors and the staff can control their own lighting and air con lol

Have they not all but hit the buffer stops now?

 

[MarkyT]

Surely all signalling has been digital since the first computer interlocking at Leamington Spa as opposed to the relay based stuff which came earlier?

The first computer based interlocking was the RETB SSI at Dingwall in 1984, which predated Leamington Spa SSI by a year.

To complicate matters, Leamington Spa was a pilot scheme and the equipment had been in situ on extended shadow mode soak test for a number of years before commissioning, in order to demonstrate the new system's safety and reliability.

The RETB application, although employing much of the the same central cubicle equipment, had a different main programme to the version used to control traditional lineside equipment.

 

[Stow]

Can someone explain to me how this works and does this mean driverless trains?

Digital signalling is broadly the modern equivalent of existing signalling, this includes ETCS specifically which is the new ‘standard’ technology to be deployed. This can include ATO functionality like Thameslink, which is very similar to CBTC systems on metros, but is only GoA2 at this time. GoA3 (DLR) and GoA4 (Glasgow subway) are not far away though.

(Grades of Automation https://en.m.wikipedia.org/wiki/Automatic_train_operation)

I expect to see GoA4 mainline trains within the next 20 years, as the technology is already fairly mature, but not necessarily widespread as humans remain key for many tasks.

Even with ‘automatic’ trains I think we need more frontline staff though, keeping the platforms safe.

All the ‘back office’ and Traffic management Digital tools are a different matter, and still immature, but have huge potential.

I’ll let other comment on more detail of the tech!

 

[carriageline]

Have they not all but hit the buffer stops now?

ROCs? Not really! Three Bridges has 12 workstations in it, I wonder if it has the highest number of panels in the country?

 

[DerekC]

Network Rail has a "Digital Railway Programme" which publishes lots of stuff online that you can read if you have a mind to. It confirms that NR's definition is more or less what has been said in this thread plus a few additional bits, i.e.:

• ERTMS/ETCS
• Traffic Management (ROCs with enhanced functionality to support more trains and improve regulation)
• C-DAS (Connected Driver Advisory System) - this is supposed to help drivers keep time and improve regulation, - connected because it gets updated timing messages from Traffic Management when the service is perturbed.
• COMPASS - this is a backup system for maintaining a service when (for example) a track circuit goes down)
• Enhanced track to train communication - not very clear what they have in mind other than it replaces GSM-R

They had £200M to spend in the current control period - not sure what's happened to it or what they are getting in the next one. Most of the effort seems to have gone into going round the planning loop for ERTMS/ETCS yet again, with little apparent result.

 

[CeeJ]

ERTMS level 2, as implemented on the Cambrian and the core of Thameslink, retains train detection by track circuits and axle counters but transmits a "movement authority" to the train instead of using signals. So if all the trains on the route have the appropriate equipment, signals are not needed (this applies to the Cambrian but Thameslink opted to keep physical signals as a backup).

Interesting question that I've not found the answer to anywhere else - but without the backup signals on platforms, what is used to indicate at CD/RA stations when the signal is 'green'?

 

[edwin_m]

I doubt the question arises on the Cambrian, but elsewhere the logical answer would be just to provide the CD/RA indicators which can be interlocked in the normal way. Being easily accessible on the platform they're less of a maintenance issue than most signals.

 

[FGW_DID]

Interesting question that I've not found the answer to anywhere else - but without the backup signals on platforms, what is used to indicate at CD/RA stations when the signal is 'green'?

The platform staff / guard has to confirm with the Driver that they have received the ‘Movement Authority’ (MA) before commencing any dispatch procedure as per Rule Book Module SS1 3.1

 

[Belperpete]

I doubt the question arises on the Cambrian, but elsewhere the logical answer would be just to provide the CD/RA indicators which can be interlocked in the normal way. Being easily accessible on the platform they're less of a maintenance issue than most signals.

On the Cambrian, the driver gives the "2 buzzes" intercom code to the guard to indicate that he has the movement authority. Usually done as soon as the train has stopped, unless waiting to cross a the train coming the other way.