SIGNALLING WITH COLOUR LIGHTS

[ForestPines]

Track circuit interlocking , for example within station limits, clearly predate TCB. Am I not correct in assuming the area so interlocked by a track circuit is in effect called the overlap

Can you give us a concrete example of such a case - where, within station limits, signal X reads to signal Y and a track circuit solely in advance of signal Y is included in the controls on signal X and prevents signal X from being cleared?

[The Stationmaster]

Ah well, if your going to ignore semantics then your wholly right, but it is the semantics that make the difference. I could for example draw a comparison between the Rocket and 87101, ignoring the semantics, they are both machines for converting energy from one form to another to extract work. Obviously they are not the same. The devil is in the detail.

Regards

Martin

 

If we are going to take the path of the devil being in the detail then I would take issue with your comment that the Clearing Point applies 'solely in Absolute Block areas' because it is clearly incorrect.   While the exact nature of it, and the distance in advance of the rearmost Home Signal varies - and in some cases has varied over the years - the term Clearing Point is also used with virtually all other block systems except TCB ranging from Train Staff & Ticket to Tokenless Block  (the latter of course, in some installations, using colour light signals with continuous track circuits in advance of the rearmost Home Signal and to or beyond the Section Signal).

 

And of course it has been the case for a good 30 years or so that at signalboxes working Absolute Block the Clearing Point has been reduced to 200 yards if the Distant signal is a colour light.

[Martin Shaw]

Yes, I take your point. I should have been more careful in my choice of phrasing but I was thinking of absolute rather than permissive, no excuse nonetheless.

I have found in my collection a booklet, regulations for signalling by TCB. This was published in 1964 and is possibly the first official reference to TCB. The 1960 SED appendix mentions TC Block but the 1960 green book doesn't.

 

Regards

Martin

[TheSignalEngineer]

Various railways issued their own instructions on a local basis to cover lines worked effectively by TCB. The BR document was standardised in 1964. Earlier examples were those like the LMS issued c1929 for Hellifield to Gargrave and the SR ones which were something like 'Working of Lines Where Block Apparatus Is Not Provided'

[The Stationmaster]

Yes, I take your point. I should have been more careful in my choice of phrasing but I was thinking of absolute rather than permissive, no excuse nonetheless.

I have found in my collection a booklet, regulations for signalling by TCB. This was published in 1964 and is possibly the first official reference to TCB. The 1960 SED appendix mentions TC Block but the 1960 green book doesn't.

 

Regards

Martin

 

Actually the term Clearing Point (and the usual Absolute Block Clearing Point) also applied in some versions of Permissive Block.

 

1964 seems to have definitely been the first issue of  nationally applicable Track Circuit Block Regulations as a Supplement to the book containing the standard Signalling Regulations.  Prior to that they were no doubt covered solely by Signalbox Special Instructions or quite possibly localised booklets applying in certain areas.  

 

The fact that the Regulations were not contained in the (so called) 'apple green' book doesn't mean they didn't exist.  We had one lot of Regulations on the Western which never went into it or the predecessor GWR (red cover) book of Signalling Regulations basically because they only applied at a handful of 'boxes - and presumably still apply at two (or did until quite recently).  Equally former GWR Regulation 4A (its number in the 1960 Regulations) with its 'Line Clear To Clearing Point Only' form of restricted acceptance was taken out of the book at the time of the 1972 reissue although it still existed (and I believe still might at one place) but only at a very limited number of places so it was a waste of time and pages putting it in a book which applies nationally and from then on it was included in Signalbox Special Instructions at those places where it was still authorised.

 

So just to round things out and provide a bit of entertainment just think of one particular signalbox which could on the same line, and depending on circumstance, accept a movement with the following bell signals (1 -4 all applied to passenger trains) -

 

1.  Repeat of 'Is Line Clear?' signal  (=full normal 'Line Clear' acceptance under AB Regulation 4),

2.  2-2-2 bell signal (= Line Clear To Clearing Point Only, acceptance under AB Regulation 4A),

3.  3-5-5 bell signal (Warning Acceptance under AB Regulation 5, Line Clear to Home Signal only) 

4.  Either 1 (most likely) or 2-4-2 bell signal to accept a train under Permissive Regulations as authorised in the Signalbox Special Instructions when the line was already occupied (I'm not sure which was authorised by the 'box Instructions as the procedure wasn't in the       Regulations at that time)

5.  3-3-2 to accept a Shunt Into forward section in accordance with ABR 31

 

Interestingly in the 1960 issue AB Regulation 31 was only included in the WR version of the book and not in that for other Regions; it was included in theirs at a later date but the procedure was used elsewhere but published only in the relevant Signalbox Special Instructions.

[Martin Shaw]

Actually the term Clearing Point (and the usual Absolute Block Clearing Point) also applied in some versions of Permissive Block.

 

1964 seems to have definitely been the first issue of  nationally applicable Track Circuit Block Regulations as a Supplement to the book containing the standard Signalling Regulations.  Prior to that they were no doubt covered solely by Signalbox Special Instructions or quite possibly localised booklets applying in certain areas.  

 

The fact that the Regulations were not contained in the (so called) 'apple green' book doesn't mean they didn't exist.  We had one lot of Regulations on the Western which never went into it or the predecessor GWR (red cover) book of Signalling Regulations basically because they only applied at a handful of 'boxes - and presumably still apply at two (or did until quite recently).  Equally former GWR Regulation 4A (its number in the 1960 Regulations) with its 'Line Clear To Clearing Point Only' form of restricted acceptance was taken out of the book at the time of the 1972 reissue although it still existed (and I believe still might at one place) but only at a very limited number of places so it was a waste of time and pages putting it in a book which applies nationally and from then on it was included in Signalbox Special Instructions at those places where it was still authorised.

 

So just to round things out and provide a bit of entertainment just think of one particular signalbox which could on the same line, and depending on circumstance, accept a movement with the following bell signals (1 -4 all applied to passenger trains) -

 

1.  Repeat of 'Is Line Clear?' signal  (=full normal 'Line Clear' acceptance under AB Regulation 4),

2.  2-2-2 bell signal (= Line Clear To Clearing Point Only, acceptance under AB Regulation 4A),

3.  3-5-5 bell signal (Warning Acceptance under AB Regulation 5, Line Clear to Home Signal only) 

4.  Either 1 (most likely) or 2-4-2 bell signal to accept a train under Permissive Regulations as authorised in the Signalbox Special Instructions when the line was already occupied (I'm not sure which was authorised by the 'box Instructions as the procedure wasn't in the       Regulations at that time)

5.  3-3-2 to accept a Shunt Into forward section in accordance with ABR 31

 

Interestingly in the 1960 issue AB Regulation 31 was only included in the WR version of the book and not in that for other Regions; it was included in theirs at a later date but the procedure was used elsewhere but published only in the relevant Signalbox Special Instructions.

   Hmm, somewhere on the Western since only they used 4A and I guess a location that joined trains so possibly Exeter West. Probably wildly wrong.

 

Regards

Martin

[The Stationmaster]

   Hmm, somewhere on the Western since only they used 4A and I guess a location that joined trains so possibly Exeter West. Probably wildly wrong.

 

Regards

Martin

 

You were - although 4A was probably in use at Exeter.  Actually it was Reading Main Line East's acceptances for the Up Main Platform Line.   Converted to colour lights just over 50 years ago - time flies.

[Junctionmad]

Can you give us a concrete example of such a case - where, within station limits, signal X reads to signal Y and a track circuit solely in advance of signal Y is included in the controls on signal X and prevents signal X from being cleared?

I cannot answer that precisely , because I haven't looked at specific interlocking tables . so while I see the TCs , I cant confirm one way or the other