How trains are signalled between Absolute Block and Track Circuit Block?

[Phil25]

Hello, this subject was definitely mentioned earlier by someone, but I'm curious - how do (and how did) modern signalling centres with digital technology communicate with signal boxes where AB was used? In one of my previous threads someone posted a picture of a signalling panel and block instruments next to it, he also mentioned that it was some kind of a temporary solution. Another thing I came across is this simsig simulation and I wanted to know how realistic it is and if it has anything to do with this topic (picture attached below).

"Hope Valley simulation which covers the Trans-Pennine Hope Valley route from the outskirts of Manchester in the west to the outskirts of Sheffield in the east. It also includes the branch to Buxton, and numerous freight-only routes linking the quarries of the Peak District. A freight-heavy simulation with lots of yard movements." (from simsig's facebook account)

 

[edwin_m]

The below is based mainly on my involvement in some of the original IECC digital signalling schemes in the early 90s.

The first manual box outside a signalling centre area is known as a fringe box. This will work Track Circuit Block to and from the signalling centre and (probably) Absolute Block to the next box in the other direction. A signalling centre can't really work AB because it requires the signaller to observe tail lamps of passing trains so as to confirm the whole train has passed by. This isn't possible in a centre controlling a large area which mostly isn't visible from the window. I can't really see how block instruments could be used in this context, but others will probably know more about that. Block bells have been used in some older power signal boxes for describing trains to and from fringe boxes, but the usual arrangement today would be for the fringe box to have a terminal to input the train descriptions of trains towards the control centre and see the descriptions of those coming from there.

With TCB there's no process of requesting and accepting trains, the train is allowed to proceed if the line is clear to the next stop signal, except in some sort of emergency system for which there is a phone link and probably an alarm to and from the signalling centre. The last signal going towards the signalling centre would have an electric lock. For a train in that direction the signaller would clear their signals if able, enter the description on the terminal, observe the tail lamp and give train out of section to the previous AB box, and just let the train proceed into the signalling centre area. In the other direction the signaller would be alerted to an approaching train in time to offer it to the next AB box, and clear their signals if it was accepted.

 

[Gloster]

The Track Circuit Block extends all the way to the manual box so that there will be no dead line before the train observed by the manual signalman, most importantly so s/he can check the taillight. At least one Stop signal in each direction at the manual box will be controlled, i.e. not capable of acting automatically.

For trains coming from the TCB area the signalman will usually see it on an illuminated diagram; what train it is will either appear on a four digit describer, actually appear on the diagram or be belled by the panel using the standard bell (or even occasionally just over a telephone, probably a direct box-to-box one); as said above, this is just indicating what train it is, not offering it as in Absolute Block. There have been cases where the panel works Absolute Block to the manual box, but this is rare except on a temporary basis.

For trains going to the TCB area the manual signalman can usually clear his Starting Signal if all the track circuits as far as the first TCB signal and its overlap are clear; sometimes he needs to get a release from the panel to do this, but usually not. He will use the same methods to tell the panel what train is going to them as they use for telling him and they will see the train appearing on their tracks.

 

[Harpo]

A small box with AB one way and TCB the other is not uncommon. I seem to recall that Chippenham Jn had this plus a third method of signalling for the Newmarket single line.

 

[MadMac]

A small box with AB one way and TCB the other is not uncommon. I seem to recall that Chippenham Jn had this plus a third method of signalling for the Newmarket single line.

Seen similar at Edinburgh, where Bathgate Central worked AB for trains coming from Edinburgh SC but TCB for trains going towards Edinburgh. Similar arrangement at Motherwell for Midcalder Junction.

 

[LowLevel]

The below is based mainly on my involvement in some of the original IECC digital signalling schemes in the early 90s.

The first manual box outside a signalling centre area is known as a fringe box. This will work Track Circuit Block to and from the signalling centre and (probably) Absolute Block to the next box in the other direction. A signalling centre can't really work AB because it requires the signaller to observe tail lamps of passing trains so as to confirm the whole train has passed by. This isn't possible in a centre controlling a large area which mostly isn't visible from the window. I can't really see how block instruments could be used in this context, but others will probably know more about that. Block bells have been used in some older power signal boxes for describing trains to and from fringe boxes, but the usual arrangement today would be for the fringe box to have a terminal to input the train descriptions of trains towards the control centre and see the descriptions of those coming from there.

With TCB there's no process of requesting and accepting trains, the train is allowed to proceed if the line is clear to the next stop signal, except in some sort of emergency system for which there is a phone link and probably an alarm to and from the signalling centre. The last signal going towards the signalling centre would have an electric lock. For a train in that direction the signaller would clear their signals if able, enter the description on the terminal, observe the tail lamp and give train out of section to the previous AB box, and just let the train proceed into the signalling centre area. In the other direction the signaller would be alerted to an approaching train in time to offer it to the next AB box, and clear their signals if it was accepted.

It's possible but unusual for "power boxes" or more modern equivalent to work absolute block, even where they can't see the train. This is achieved either by use of tail lamp cameras or equipment for the crew to confirm that they've arrived complete.

Two examples I know of are Worksop which works absolute block to Shirebrook Junction using tail lamp cameras, and Chinley which works absolute block to Edale and Peak Forest South Junction with tail lamp cameras.

 

[Harpo]

It's possible but unusual for "power boxes" or more modern equivalent to work absolute block, even where they can't see the train. This is achieved either by use of tail lamp cameras or equipment for the crew to confirm that they've arrived complete.

Two examples I know of are Worksop which works absolute block to Shirebrook Junction using tail lamp cameras, and Chinley which works absolute block to Edale and Peak Forest South Junction with tail lamp cameras.

Tail lamp cameras can also be used on all-AB territory. I think Craven Arms had (has??) one for a loop in rear of the box?

 

[matchmaker]

Aberdeen SC worked AB one direction to Newtonhill. The other direction was TCB. Motherwell SC worked AB to one of the fringe boxes - forget which one. There were other examples, and there was a discussion recently somewhere about this - again I can't remember where!

 

[frankmoh]

I would like to know how the Addiscombe box worked in conjunction with the London Bridge signalling centre in the 70s, 80s and 90s.

 

[MadMac]

Aberdeen SC worked AB one direction to Newtonhill. The other direction was TCB. Motherwell SC worked AB to one of the fringe boxes - forget which one. There were other examples, and there was a discussion recently somewhere about this - again I can't remember where!

Motherwell worked AB to Midcalder Junction on the Down line from Carstairs.

 

[matchmaker]

Motherwell worked AB to Midcalder Junction on the Down line from Carstairs.

Thanks @MadMac . I remember the "Block Instrument" being built into the NX panel in Motherwell SC.

 

[172007]

Tail lamp cameras can also be used on all-AB territory. I think Craven Arms had (has??) one for a loop in rear of the box?

Droitwich Spa also has a tail lamp camera on the Down so when a train arrives in the platform (before the box) another can be accepted from Tunnel Jct as that direction is Absolute Block. The other direction is AB with track circuit due to the Intermediate Block signal.

On the Down after the platform it then becomes track curcuit for the fringe to BROC (Birmingham Regional Operations Centre) Stourbridge workstation.

 

[MadMac]

Thanks @MadMac . I remember the "Block Instrument" being built into the NX panel in Motherwell SC.

Similar arrangement at Edinburgh for trains going to Bathgate Central. The arrangement lives on in a way at Inverness which works Tokenless Block to Keith and, I think, Insch. Possibly the same on the Pitlochry workstation at Stanley Junction?

 

[Tony73E]

I'm not a Signaller so some of my description may be iffy but prior to abolition as part of East Kent Resignalling, Faversham box worked TCB with Margate in one direction and Sittingbourne in the other. However, it worked AB with Canterbury East on the line to Dover. Faversham box had a shelf behind the main panel on which were the block bells. On the main panel was an acceptance button for trains offered from Canterbury East and a bell push for offering trains to Canterbury.

Faversham panel was interesting in that when points were operated the indication on the panel moved as well to show the route set. This panel is now housed in the box formally at Selling which has been moved to Eythorne on the East Kent Railway.

 

[MadMac]

Faversham panel was interesting in that when points were operated the indication on the panel moved as well to show the route set. This panel is now housed in the box formally at Selling which has been moved to Eythorne on the East Kent Railway.

British Transport Film “The Signal Engineers” shows these at Barking at about the 23 minute mark.