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Question about control of a section

Current and future British signalling (UK except Northern Ireland)

Question about control of a section

Unread postby Dot93 » Sun Oct 23, 2016 10:35 am

Just a question from a novice if you can help please? Once a train has passed a section signal, isn't that section worked / owned by the box in rear? (The box last passed) Even though the box in rear needs permission from the box ahead before the train is let into the section?


So from a driver or guards point of view, if they had to contact the signaller for something whilst in the section, they would contact the box in rear unless they had passed the distant for the box ahead?


Apologies if the info to clarify this is on the Web site / forum but I couldn't find it when looking through. I've heard some say that the box ahead controls the section in rear but also that the box in rear controls the section ahead?
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Re: Question about control of a section

Unread postby Richard Lemon » Sun Oct 23, 2016 1:53 pm

The term "owned" is an unusual one, but to put it simply, the box in advance works the block for the section, and gives permission for ait to be occupied, so I suppose you could say that it is "owned" by that one.

If a train fails, the driver would use radio, but if this was not available, the guard would go to the nearest telephone (at a crossing perhaps) or the nearer of the signal boxes. If he needed to protect the train, he would walk back towards the box in rear.

I hope this gives some clarity in relation to Absolute Block.
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Re: Question about control of a section

Unread postby Dot93 » Sun Oct 23, 2016 3:56 pm

Thank you, after speaking to a couple of drivers they clarified what I thought initially, that when something goes wrong in the section, you always contact the box in rear.
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Re: Question about control of a section

Unread postby Richard Lemon » Sun Oct 23, 2016 4:51 pm

But, if it is easier to contact the box in advance (such as at a level crossing telephone) you would do so.
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Re: Question about control of a section

Unread postby Mike Hodgson » Mon Oct 24, 2016 2:03 am

Just to clarify the distant signal of the box in advance is irrelevant and it does not mark the end of the section.

The section runs from the most advanced starting signal to the outermost home signal of the box in advance. Once you have passed that home signal you are within station limits at the box in advance, although the section itself would still be considered to occupied or obstructed until have cleared the 1/4 mile overlap.

Absolute Block is no longer the norm - most of network, especially the busiest routes, is worked by Track Circuit Block, so nowadays there are fewer long stretches of "no man's land" where your location would not be indicated in one box or another. On the other hand you may be much further from the controlling signalling box than in mechanical days. The availability of communications is so much more important now, and on health & safety grounds it is preferred that you use the radio or failing that a telephone rather than walking the line to climb the signalbox stairs.
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Re: Question about control of a section

Unread postby Dot93 » Mon Oct 24, 2016 12:33 pm

Thank you for your helpful answers and input. Cheers.
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Re: Question about control of a section

Unread postby StevieG » Sun Nov 20, 2016 8:03 pm

Hoping to be of further help, Dot93, whilst not moving to things of which you may already be aware; - carrying the foregoing points about Absolute Block etc. into Track Circuit Block matters,
on the vast majority of TCB running lines the signal section from one main stop signal to the next is the equivalent of the archetypal 'most advanced starting signal of one box to the outermost home signal of the next box in advance', box-to-box AB section.
Whilst out of any group of these signal sections, mostly, they will be under the control or supervision of one single signaller, there are, in areas signalled from multi-staffed, moderate-large signal control centres*, inevitably some sections which effectively form the hand-over point between individual signallers' areas of either the same, or different, SCCs.
* - (the term 'signal control centres' can apply equally to control locations variously known as 'power box', 'power signal box', 'signalling centre', 'area signalling centre', 'rail operations centre', and possibly others.)

Traditionally (say approx. 1930s - 80s) most TCB series of automatic and semi-automatic signals between areas of directly controlled signals, and therefore also their Signal Post Telephones, were considered and arranged to be the responsibility of the 'advance' signalman whose next directly manually controlled area ahead they were on the approach to, and this meant that the Up and Down signals in such 'hand-over' areas were supervised by different signalmen. But with the advent of electronic / computer-based, rather than relay, interlockings, and engineering considerations bringing about a preference for interlocking (and so, usually, signallers) boundaries to be at roughly the same place on all tracks, the 'approach to' practice mostly no longer holds good for new works from approx. the 1990s onwards.

Now, concerning the question of 'rear or advance signaller' protection and contact in case of mishap, TCB systems should automatically protect in rear of a train in all but the most exceptional circumstances.
As regards drivers' communications in the event of problem, SPTs, and where provided other lineside 'phones, normally connect directly to the relevant signaller.
But AIUI all traction types on the network are now required to be equipped with working radio system(s) of one or other kind (can be more than one : - but I believe well on the way to universal provision and use of the GSM-R system), which include affording discrete direct communication to the signaller and are usually arranged to automatically ensure driver-initiated contact goes to a correct signaller for the location, including priority emergency call ability; also of these, the GSM-R system in case of emergency can simultaneously alert more than one signaller who may, depending on circumstances, be in a position to initiate appropriate safety action.

Hope all this waffle is of help / interest, while doubtless there may be clarifications / comments which others can add.
Last edited by StevieG on Wed Nov 23, 2016 12:57 am, edited 1 time in total.
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Re: Question about control of a section

Unread postby edwin_m » Tue Nov 22, 2016 11:10 pm

I have always assumed that the modern practice of putting a control boundary in the same place on all tracks, rather than having tracks in each direction controlled by the signaller the train is heading towards, arose from the need to replace signals on all lines as quickly as possible if one of them has an emergency. But I don't actually know this. Another helping factor would be the ubiquity of displays allowing the signaller to see train positions outside their area, so they can still make regulating decisions without having to have the plain line approaching their first junction actually within their area of control. It must also simplify GSM-R if the system can select the correct signaller to route a call to simply by geographic position along a route, without having to take account of which direction a train is moving or which track it is on.
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Re: Question about control of a section

Unread postby John Hinson » Wed Nov 23, 2016 8:53 am

You are right, managing trains at the border areas at times of incident was always difficult but in areas of smaller boxes it gave better warning of the approach of trains for regulation purposes. But I wouldn't be surprised the policy change was for new technology and not for the benefit of operators.

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