Signalling question: Intermediate block signals on the former Southern Region

[Annetts key]

On the question of two Intermediate Block signals, that requires multiple track circuits. In which case, it is likely to be seen to be better to move to track circuit block with automatic signals between the remaining signal boxes. This was the method used on Western Region in the run up to the big (for then) MAS PSB schemes.

Both because it allowed far more signal boxes to be closed without reducing the line capacity and because it made re-control to a MAS PSB a whole lot easier when the time came.

 

[MarkyT]

On the question of two Intermediate Block signals, that requires multiple track circuits. In which case, it is likely to be seen to be better to move to track circuit block with automatic signals between the remaining signal boxes. This was the method used on Western Region in the run up to the big (for then) MAS PSB schemes.

Both because it allowed far more signal boxes to be closed without reducing the line capacity and because it made re-control to a MAS PSB a whole lot easier when the time came.

And early auto sections had few indications back to the controlling box, usually only track circuit status repeats. In 1960s/70s schemes these were often carried in a distributed non-vital reed FDM system to carry maximum numbers of channels in the minimum number of cable pairs. Reconfiguring such a system requires only the 'office' end to be relocated to the new PSB during the recontrol.

 

[Islineclear3_1]

Thanks everyone for your replies

 

[Controller1701]

I can confirm that Bexhill signalbox was able to switch out of circuit, and indeed for a number of years it would only switch in when required for engineering works. During this time the block section would be St Leonards West Marina (SL) until that closed and then Bopeep Junction(BJ) to Pevensey & Westham. I recall that it was the intorcuction of the Ashford International to brighton services that resulted in Bexhill being open on a regular basis during the day.

 

[Islineclear3_1]

Wasn't Bexhill switched out on Sundays?

 

[Sunset route]

Further along, I wonder if BK41 at Glynde was an IB signal when Glynde box was abolished. I remember a switch in Berwick signal box

As Berwick-Lewes was TCB, BK 41 was probably not an IBS. It may have been a semi-automatic.

BK41 was shown on Berwick's diagram as an automatic signal, with a replacement switch and a "fog switch", whatever one of those is. As you suggest, you can't have an IBH in a TCB section!

BK41 as was BK39 both automatic signals with replacement switches. When BK15 the Down Distant was a semaphore under and AB regs for working during fog and falling snow you were not allowed to let a train leave Glynde until the train had been accepted by Polegate Crossing Box (double block working).

So when the fog switch for BK41 placed into it’s working condition and the replacement for BK41 was switch to ON the signal would be held at danger as per normal. Then once Polegate had accepted the train you could switch BK41 to OFF and it would clear. The train would replace it to danger with the occupation of the track circuits but instead of charging back like an automatic signal normally would when those tracks circuits cleared again it would remain at danger, until the replacement switch was switched to ON then switch to OFF if Polegate had accepted the next train. So the fog switch turned BK41 into a controlled signal when double block working was required.

 

[Townsend Hook]

Are there any more intermediate block signals still working on the Southern, other than Bognor’s BR14?

 

[Controller1701]

EDL 74 on the up at St Leonards Warrior Square