How are track circuits / signals wired together?

[RailDepartures]

Bit of a strange question which Iv tried to research but can’t find the exact answer but hoping someone in the industry here will know the answer.

Basically I understand how each track block section is hard wired to the signal protecting it via a relay and how the train shorts the tracks out etc on the older style block sections.

The bit of information I can’t find is how does this data make its way into the network rail computer system?

All these little track blocks must be wired up to something else which monitors them? Then passes this data on? But how?

Is this what they call the signal boxes? Like mentioned here?

Alextrack: Railways: Signalling

Are a group of block sections all wired back to a single signal box? (Just a track side cabinet?) and then all these signal boxes are then wired together somehow? But then how does this data get into the main computer system? Does the railway have its own hardwired network? Or it goes over the internet?

I’d really like to understand how the data gets from a single on/off track block section all the way back to the main computer system (all steps and layers of infrastructure involved, types of wire, data protocols, hardware etc…)

Any information or detailed explanation would be much appreciated.

 

[Gloster]

What you appear to have here is a list of the former, mostly manual (i.e. lever), signal boxes that were closed when they were all replaced by Bristol Panel Signal Box at the beginning of the 1970s. These boxes communicated by bells and, with a couple of exceptions, there were not track circuits between them. Trains were signalled by bell signals between the boxes and their progress was followed by each box observing the train as it passed, sending the appropriate bell signals and the signalman seeing the tail lamp to check the train was complete.

Your list has not been relevant to the current type of signalling, which for this area was all controlled from Bristol Panel. I am not sure, but I think part of this is still in operation.

 

[RailDepartures]

What you appear to have here is a list of the former, mostly manual (i.e. lever), signal boxes that were closed when they were all replaced by Bristol Panel Signal Box at the beginning of the 1970s. These boxes communicated by bells and, with a couple of exceptions, there were not track circuits between them. Trains were signalled by bell signals between the boxes and their progress was followed by each box observing the train as it passed, sending the appropriate bell signals and the signalman seeing the tail lamp to check the train was complete.

Your list has not been relevant to the current type of signalling, which for this area was all controlled from Bristol Panel. I am not sure, but I think part of this is still in operation.

Ah I see, ok that helps thanks. Do signal boxes still exist at all? Or everything is just wired together using those little track side cabinets you see along the edge of the railway?

 

[Gloster]

Ah I see, ok that helps thanks. Do signal boxes still exist at all? Or everything is just wired together using those little track side cabinets you see along the edge of the railway?

Old ‘manual’ signal boxes still exist dotted in clumps around the network, but they are slowly being replaced by more modern types. However, this replacement has been going on for years and the replacements have gone through several generations of technology, so much so that some of the older replacements are having to be replaced more urgently than the older manual boxes, which keep going because of their simple technology.

All the network is controlled or supervised by a signal box of one sort or another: more modern ones are likely to have a fairly exact knowledge of where a train is, older ones just know ‘it passed X at 12.34 and hasn’t got to Y yet’. The line side cabinets just hold the various connections and terminals for small areas in one place. (Others can better explain the technical side of things: I was an operator.)

Have a stroll through the Wikipedia pages on Railway Signalling: you may have to go through a number of pages and go back and forth sometimes to see how it all ties up. Also, make sure that you don’t find yourself reading about other countries’ systems, particularly the US, as they are different.

 

[RailDepartures]

Old ‘manual’ signal boxes still exist dotted in clumps around the network, but they are slowly being replaced by more modern types. However, this replacement has been going on for years and the replacements have gone through several generations of technology, so much so that some of the older replacements are having to be replaced more urgently than the older manual boxes, which keep going because of their simple technology.

All the network is controlled or supervised by a signal box of one sort or another: more modern ones are likely to have a fairly exact knowledge of where a train is, older ones just know ‘it passed X at 12.34 and hasn’t got to Y yet’. The line side cabinets just hold the various connections and terminals for small areas in one place. (Others can better explain the technical side of things: I was an operator.)

Have a stroll through the Wikipedia pages on Railway Signalling: you may have to go through a number of pages and go back and forth sometimes to see how it all ties up. Also, make sure that you don’t find yourself reading about other countries’ systems, particularly the US, as they are different.

Yeah it’s just the UK systems I’m interested in, I’m guessing ones from the 80s? (Still in use today) lines like Bristol Temple Meads to Weston Super Mare or Severn Beach line which I believe are all the voltage controlled block section technology.

 

[Gloster]

Yeah it’s just the UK systems I’m interested in, I’m guessing ones from the 80s? (Still in use today) lines like Bristol Temple Meads to Weston Super Mare or Severn Beach line which I believe are all the voltage controlled block section technology.

I have never before heard that being used: I have always known it as Track Circuit Block and that is what it was called in the Signalling Regulations. I believe that the signalling from Temple Meads and eastwards to the Panel’s limit of control by the 1970 Bristol Panel was resignalled before the recent overhead electrification, but south/west of Bristol resignalling was not carried out at the same time, although I am not sure if it since has been.

Additionally, have a look at the Signalling Block System page on Wikipedia: Manual Block System - Telegraph Block will give you the basis of the system that is still in use, while the Automatic Block System page will tell you more about more modern systems.

 

[John Webb]

British railways, being the first in the world, also developed signalling. British signalling evolved over the years, and the mechanical manual signalling system was first modified by adding 'interlocking' between the levers to minimise mistakes by the signalman.
As electricity came along adaptions of the electric telegraph to allow communications between boxes introduced the block or 'space' separation of trains rather than the previous 'time interval' system.
Mainly as a result of accidents, electrical interlocking was added to mechanical lever systems to improve safety and this was further enhanced by the introduction of track circuits.
Power systems were developed with at first mechanical levers working switches and still with mechanical interlocking, but eventually relay interlocking worked from panels with switches on came in, followed in more recent times by computer control and modern electronic interlocking.

"Two Centuries of Railway Signalling" (Kitchenside and Williams, Oxford Publishing Co., 1998, ISBN 0 86093 541 8) and "An Illustrated History of Signalling" (Michael A. Vanns, Ian Allan, 1997, ISBN 0 7110 2551 7) give a good background to the above developments.

 

[RailDepartures]

After a bit more research I found this blog, this guy developed some of the older systems and shows some of the cards which tracked the stepping of the trains from one track section to another but does not really go into detail on how the sections was wired together.

bygonebytes

I’m not sure if this type of tech is still used on some parts of the railway or it’s all been replaced but I’m sure the original track sections are still in place and must all wire up to something. Which is then wired up to something else.

 

[John Webb]

After a bit more research I found this blog, this guy developed some of the older systems and shows some of the cards which tracked the stepping of the trains from one track section to another but does not really go into detail on how the sections was wired together.

bygonebytes

I’m not sure if this type of tech is still used on some parts of the railway or it’s all been replaced but I’m sure the original track sections are still in place and must all wire up to something. Which is then wired up to something else.

The article you linked to is about the way the signaller is given information about the train and its location. This is a development from just knowing what 'class' of train is approaching one box from another through the old bell codes to knowing the train's actual 'reporting number' as defined in the timetable. The article deals with displays on physical panels; many now replaced by computer screens.
Such information is available on sites such as 'Traksy' and 'Real Time Trains' where you can select a station or area and see the passage of trains on the move.

 

[RailDepartures]

Yeah, it’s not quite the information I am after I am hoping someone in the industry here would know the exact answers.

The above blog says this “

Greenhill Train Describer - 1990​

Greehill Train Describer was a 64 berth/80 step describer with the backplane wired as a 64 berth/128 steps and once again added more features such as a VDU display instead of the traditional four character display modules and links to TRUST.”

Which suggests one TD can look after up to 64 track sections? (In this example?) that would be some pretty long distances for the cabling?

The TDs deffo exist in today’s infrastructure as they are mentioned a lot in the feeds. I just want to know how they monitor / are connected to the various berth track circuits and how the data is passed about.

 

[68000]

In simple terms:

For relay room areas - Multicore signalling cables along the track are brought into the signalling location cases dotted about. At these location cases, circuit functions are introduced, joined, passed through or terminated. The indications for a train describer and signaller panel will be brought back to a relay room and transmitted back to the controlling signal box / centre over a multiplexor system (TDM). Signaller commands are also sent through the TDM. Sometimes FDM is used along trackside cables where there are long automatic signal sections.

In computer based interlocking areas, datalink cables (either copper or fibre optic) replace multicore signalling cables and are locally distributed as above.

What you can gather from this is the fact that there are signalling cables along the majority of the rail network (as well as power and telecoms cables)

 

[Annetts key]

The thing that ties the signals to the track circuits and the points is the interlocking.

However, technically speaking, the safety critical interlocking may not deal with all indications to the signaller or with data / information used to feed other systems (such as train describer -TD).

Over the years, the technology has changed but the basic principles are more or less the same.

with a mechanical signal box, there was a mechanical locking frame. In addition, some levers may have had electrical lever locks (actually electro-magnetic). Combined, these proved either mechanically or electrically that the required conditions are correct before the signaller could move the relevant lever.

Relay interlocking for a controlled signal area does something similar. It has feeds in for all track circuits, electrical detection for all points, etc. Then a complex logic system determines If a signal can clear, and if yes, which aspect should be displayed.

For most automatic signals on plain line in the middle of nowhere (except where part of a computer based signalling system), instead of a large interlocking, instead smaller installations are used in the lineside cupboards.

Non-safety indication circuits repeat the track circuit status or other status information back to the relevant signal box or PSB for display on the signallers track diagram or panel. And for use by the TD.

With computer based interlocking, systems like the British developed SSI (Solid State Interlocking) and later systems use communication links between electronic modules in the lineside cupboards to a central computer based interlocking. That performs all the functions of a relay based interlocking. It then feeds data to other computer systems. One of which is the signallers interface. Another is the TD.

Note that in mechanical signal boxes a manual data entry system may be used. Or those that have a TD system and in PSB it's the TD system that feeds the data to other Network Rail computer systems.

A subset of the data will be fed to other systems, some of which appear as the Network Rail 'public' datafeeds.

What you appear to have here is a list of the former, mostly manual (i.e. lever), signal boxes that were closed when they were all replaced by Bristol Panel Signal Box at the beginning of the 1970s. These boxes communicated by bells and, with a couple of exceptions, there were not track circuits between them. Trains were signalled by bell signals between the boxes and their progress was followed by each box observing the train as it passed, sending the appropriate bell signals and the signalman seeing the tail lamp to check the train was complete.

Your list has not been relevant to the current type of signalling, which for this area was all controlled from Bristol Panel. I am not sure, but I think part of this is still in operation.

Yes, that's some of the signal boxes that Bristol Panel (PSB) replaced.
Most of the area controlled by Bristol Panel has transferred to TVSC (Thames Valley Signalling Centre). But Bristol Panel still controls the main line and branches between Flax Bourton (just east of Nailsea and Backwell) to Fordgate / Meads Crossing (just south of Bridgwater). The relevant remote relay interlockings being: Bridgwater, Highbridge, Uphill Junction, Weston-super-Mare, Worle Junction and Yatton.

Yeah it’s just the UK systems I’m interested in, I’m guessing ones from the 80s? (Still in use today) lines like Bristol Temple Meads to Weston Super Mare or Severn Beach line which I believe are all the voltage controlled block section technology.

Forget the term "voltage controlled block section technology", it's something I have never heard of, and I was involved with the technical side of British railway signalling for over 35 years.

Specifically, for the Weston-super-Mare area:

Weston-super-Mare has a relay interlocking near the station. All track circuits and point detection feed back to the relay interlocking via local location cupboards and then via lineside multicore cables. Similarly, feeds originate from the relay interlocking to control each signal and the two point machines, also for the one remaining ground frame (GF). Most of these are safety DC control circuits (there are also some AC circuits).

The relay interlocking thus controls all the signals in the area, the two point machines and the release for the GF. The relay interlocking uses BR specification safety type signalling relays.

Being a 1972 vintage BR Western Region design, the relay interlocking also has a large number of non-safety relays, called PO (Post Office) relays. These were built using similar relay parts that were once common in GPO telephone exchanges. These are used for the non-safety functions and to interface to and from a TDM system.

In the same building as the interlocking, there is a communication system. This is a Time Division Multiplex (TDM) system. This receives control instructions from Bristol Panel PSB and sends indications and status information to Bristol Panel PSB.

A TDM converts an incoming serial data stream from a telecommunication link into multiple parallel outputs, each of which feeds into the relay interlocking.

The TDM also converts multiple parallel inputs to a serial data stream, which it then sends out via a telecommunication link. The multiple parallel inputs being outputs from the relay interlocking or from PO relay contacts.

The telecommunication link is part of Network Rails telecommunications infrastructure. These can be multicore copper telecommunications cables or these days, fibre-optic telecommunications cables.

The telecommunication link goes to Bristol Temple Meads station, which is where Bristol Panel PSB is located. This building also houses the railway Bristol Telephone Exchange and the Bristol Temple Meads Interlocking.

The telecommunication link goes to the exchange, then to the interlocking room, where there is another TDM system.

This TDM has inputs from yet more PO relays and direct inputs from some of the switches on the signallers panel. The PO relays act as both an interface between the signallers panel switches and buttons and it performs some sanity checking of the instructions from the signaller.

The outputs from the TDM are fed to more PO relays. These then feed track circuit indication lamps, signal indication lamps, point indication lamps and various other indications on the signallers panel. They also control some audible warning alarms and the small number of dying pig (train approaching buzzers).

These PO relays also feed the TD system that is also contained in the same building. The TD has it's own telecommunication links to the TD systems at Exeter PSB and to TVSC. This is so that one system can pass train descriptions to another system when needed. Such as when a train is approaching the area of control of the signal box / PSB / control centre.

The TD has an OCU (operators control unit) where the signaller can enter, overwrite, manually step or cancel train descriptions (head codes).

The objective of the TD is to automatically move train descriptions each time a train moves from one track circuit block section to another section, without the intervention of the signaller. Hence it needs to know the status of the relevant track circuits, if the signal is showing a proceed aspect and if the signal has more than one route available, which route the signaller selected. It gets this information from the PO relays that I talked about above.

In addition to the telecommunication links to the other TD systems, there is a link to the Network Rail TRUST system. But this data feed also feeds other Network Rail train running computer systems.

And it is from these systems that the data for the Network Rail 'public' data feeds is obtained.

Please note that with the different technologies in use, elsewhere, the details will may be different. Take the lines that BTM to Severn Beach trains use. Part is controlled by TVSC and part is controlled by St. Andrews Junction signal box. At St. Andrews Junction signal box, there are two panels (no levers left now), one of which controls relay interlocking and one controls SSI. Then on the section between St. Andrews Road station and Severn Beach, there is more relay interlocking.

 

[RailDepartures]

In simple terms:

For relay room areas - Multicore signalling cables along the track are brought into the signalling location cases dotted about. At these location cases, circuit functions are introduced, joined, passed through or terminated. The indications for a train describer and signaller panel will be brought back to a relay room and transmitted back to the controlling signal box / centre over a multiplexor system (TDM). Signaller commands are also sent through the TDM. Sometimes FDM is used along trackside cables where there are long automatic signal sections.

In computer based interlocking areas, datalink cables (either copper or fibre optic) replace multicore signalling cables and are locally distributed as above.

What you can gather from this is the fact that there are signalling cables along the majority of the rail network (as well as power and telecoms cables)

Fantastic thank you

The thing that ties the signals to the track circuits and the points is the interlocking.

However, technically speaking, the safety critical interlocking may not deal with all indications to the signaller or with data / information used to feed other systems (such as train describer -TD).

Over the years, the technology has changed but the basic principles are more or less the same.

with a mechanical signal box, there was a mechanical locking frame. In addition, some levers may have had electrical lever locks (actually electro-magnetic). Combined, these proved either mechanically or electrically that the required conditions are correct before the signaller could move the relevant lever.

Relay interlocking for a controlled signal area does something similar. It has feeds in for all track circuits, electrical detection for all points, etc. Then a complex logic system determines If a signal can clear, and if yes, which aspect should be displayed.

For most automatic signals on plain line in the middle of nowhere (except where part of a computer based signalling system), instead of a large interlocking, instead smaller installations are used in the lineside cupboards.

Non-safety indication circuits repeat the track circuit status or other status information back to the relevant signal box or PSB for display on the signallers track diagram or panel. And for use by the TD.

With computer based interlocking, systems like the British developed SSI (Solid State Interlocking) and later systems use communication links between electronic modules in the lineside cupboards to a central computer based interlocking. That performs all the functions of a relay based interlocking. It then feeds data to other computer systems. One of which is the signallers interface. Another is the TD.

Note that in mechanical signal boxes a manual data entry system may be used. Or those that have a TD system and in PSB it's the TD system that feeds the data to other Network Rail computer systems.

A subset of the data will be fed to other systems, some of which appear as the Network Rail 'public' datafeeds.


Yes, that's some of the signal boxes that Bristol Panel (PSB) replaced.
Most of the area controlled by Bristol Panel has transferred to TVSC (Thames Valley Signalling Centre). But Bristol Panel still controls the main line and branches between Flax Bourton (just east of Nailsea and Backwell) to Fordgate / Meads Crossing (just south of Bridgwater). The relevant remote relay interlockings being: Bridgwater, Highbridge, Uphill Junction, Weston-super-Mare, Worle Junction and Yatton.


Forget the term "voltage controlled block section technology", it's something I have never heard of, and I was involved with the technical side of British railway signalling for over 35 years.

Specifically, for the Weston-super-Mare area:

Weston-super-Mare has a relay interlocking near the station. All track circuits and point detection feed back to the relay interlocking via local location cupboards and then via lineside multicore cables. Similarly, feeds originate from the relay interlocking to control each signal and the two point machines, also for the one remaining ground frame (GF). Most of these are safety DC control circuits (there are also some AC circuits).

The relay interlocking thus controls all the signals in the area, the two point machines and the release for the GF. The relay interlocking uses BR specification safety type signalling relays.

Being a 1972 vintage BR Western Region design, the relay interlocking also has a large number of non-safety relays, called PO (Post Office) relays. These were built using similar relay parts that were once common in GPO telephone exchanges. These are used for the non-safety functions and to interface to and from a TDM system.

In the same building as the interlocking, there is a communication system. This is a Time Division Multiplex (TDM) system. This receives control instructions from Bristol Panel PSB and sends indications and status information to Bristol Panel PSB.

A TDM converts an incoming serial data stream from a telecommunication link into multiple parallel outputs, each of which feeds into the relay interlocking.

The TDM also converts multiple parallel inputs to a serial data stream, which it then sends out via a telecommunication link. The multiple parallel inputs being outputs from the relay interlocking or from PO relay contacts.

The telecommunication link is part of Network Rails telecommunications infrastructure. These can be multicore copper telecommunications cables or these days, fibre-optic telecommunications cables.

The telecommunication link goes to Bristol Temple Meads station, which is where Bristol Panel PSB is located. This building also houses the railway Bristol Telephone Exchange and the Bristol Temple Meads Interlocking.

The telecommunication link goes to the exchange, then to the interlocking room, where there is another TDM system.

This TDM has inputs from yet more PO relays and direct inputs from some of the switches on the signallers panel. The PO relays act as both an interface between the signallers panel switches and buttons and it performs some sanity checking of the instructions from the signaller.

The outputs from the TDM are fed to more PO relays. These then feed track circuit indication lamps, signal indication lamps, point indication lamps and various other indications on the signallers panel. They also control some audible warning alarms and the small number of dying pig (train approaching buzzers).

These PO relays also feed the TD system that is also contained in the same building. The TD has it's own telecommunication links to the TD systems at Exeter PSB and to TVSC. This is so that one system can pass train descriptions to another system when needed. Such as when a train is approaching the area of control of the signal box / PSB / control centre.

The TD has an OCU (operators control unit) where the signaller can enter, overwrite, manually step or cancel train descriptions (head codes).

The objective of the TD is to automatically move train descriptions each time a train moves from one track circuit block section to another section, without the intervention of the signaller. Hence it needs to know the status of the relevant track circuits, if the signal is showing a proceed aspect and if the signal has more than one route available, which route the signaller selected. It gets this information from the PO relays that I talked about above.

In addition to the telecommunication links to the other TD systems, there is a link to the Network Rail TRUST system. But this data feed also feeds other Network Rail train running computer systems.

And it is from these systems that the data for the Network Rail 'public' data feeds is obtained.

Please note that with the different technologies in use, elsewhere, the details will may be different. Take the lines that BTM to Severn Beach trains use. Part is controlled by TVSC and part is controlled by St. Andrews Junction signal box. At St. Andrews Junction signal box, there are two panels (no levers left now), one of which controls relay interlocking and one controls SSI. Then on the section between St. Andrews Road station and Severn Beach, there is more relay interlocking.

This is exactly what I was after thank you so basically all local signals in an area are connected to a local TDM which then gathers the signal states and converts the data to some serial packet and sends it via a single telecommunications cable (which runs full distance of all the tracks?) back to Bristol Temple Meads (Bristol Panel) for this particular area which then processes this data and passes it along to other systems? (Over the internet at this point?)

 

[Annetts key]

This is exactly what I was after thank you so basically all local signals in an area are connected to a local TDM which then gathers the signal states and converts the data to some serial packet and sends it via a single telecommunications cable (which runs full distance of all the tracks?) back to Bristol Temple Meads (Bristol Panel) for this particular area which then processes this data and passes it along to other systems? (Over the internet at this point?)

Basically yes.

 

[MarkyT]

Large central panel signal boxes controlling several remote relay interlockings became the dominant system architecture from the 1950s until the late 1980s, when SSI began to make inroads after the successful Leamington Spa pilot scheme. Individual remote interlockings cover a logical grouping of points and signals around a junction or station. The safety relays and telemetry equipment are housed in lineside buildings called interlockings or relay rooms and these also act as power distribution hubs for the local equipment cabinets dotted around the layout. Remote control telemetry links the panel and its interlockings to exchange commands and status indications, typically using TDM techniques over two telecom pairs but sometimes a massive multipair cable is used to interlockings not too far away, as electronics was expensive in the 1960s. TDM was always preferred for longer distance for timing reasons. Direct relay circuits have length limits and repeat relays would lead to unacceptably slow response times.

At the panel end, the telemetry would typically interface via relays again to the switches and lights of the control panel. Train describer systems often took their input from contacts of the same panel relays or in modern systems they could take a direct serial feed from the remote control telemetry. The train describer system in the signalbox directly controls the signallers TD indications on the panel or associated screens and forwards a live version of events on the map to a central NR database that powers internal management and info systems and presents a version of them as an open data feed for third party use by Open Train Times, Traksy, etc.

These concepts were pioneered in 1927 by the US General Railway Signal company with their CTC (centralized traffic control) system. With the same central panel and remote interlocking arrangement, it was limited by a fairly slow and clunky telemetry system based on relays, selectors etc. like early telephone exchanges. Nonetheless it became wildly popular over there in the 30s and 40s, where railroads were able to squeeze more capacity out of their systems by better managing movements from more centralised control locations with a bigger picture.

 

[norbitonflyer]

What you appear to have here is a list of the former, mostly manual (i.e. lever), signal boxes that were closed when they were all replaced by Bristol Panel Signal Box at the beginning of the 1970s. These boxes communicated by bells and, with a couple of exceptions, there were not track circuits between them. Trains were signalled by bell signals between the boxes and their progress was followed by each box observing the train as it passed, sending the appropriate bell signals and the signalman seeing the tail lamp to check the train was complete.

Historically, the manual signal boxes would not be wired into any central system - there would be electrical communication between adjacent boxes as part of the block system (and single line control where this was used), and probably a telephone to allow communication with "Control" to pass instructions and report problems.

The actual train movements would be recorded in a log book and only reported to Control periodically (for example when the book was full?) or if needed for an investigation into an incident. (One of the contributory causes of the Quintinshill disaster in 1915 was that the signalman who had just come on duty was busy copying the records his colleague had made on a piece of paper into the log so that the handwriting didn't reveal that he had come on duty late)

 

[John Webb]

...The actual train movements would be recorded in a log book and only reported to Control periodically (for example when the book was full?) or if needed for an investigation into an incident. (One of the contributory causes of the Quintinshill disaster in 1915 was that the signalman who had just come on duty was busy copying the records his colleague had made on a piece of paper into the log so that the handwriting didn't reveal that he had come on duty late)

The 'Log Book' was formally known as the "Train Register Book" (TRB). When full a new one would be started and the old placed on one side.
Signal boxes were visited at least once a week by either the local signalling inspector and/or the stationmaster, who would check on the signaller, see that the TRB was being completed correctly, and indeed would sign it to show when they had called in.

Most contact with 'Control' was done over 'omnibus' telephone lines which linked control with a number of boxes and stations and on which messages about delayed or cancelled trains could be passed to and fro.
Some boxes had specific 'Reporting' duties and would usually inform control of trains passing them by phone - this was often at a divisional boundary and was to ensure one division couldn't blame another for the late running of a train!