Signalling and the 1876 Abbotts Ripton Accident
Posted: Sat Dec 31, 2011 1:24 am
I had originally posted the following as background info to this accident in the "Accidents involving the train Flying Scotsman" thread in the 'LNER Discussion' >> "LNER Locomotives and Rolling Stock" forum, but got a bit carried away and ended up thinking that it was inappropriate for that forum, so have moved it here as a new thread : -
[* - This was when what is sometimes called 'open' block was still in use; i.e., although the signal boxes were in telegraphic communication for signalling trains, as soon as one signalman received 'train out of section' from the box ahead, the status of the block section was regarded as clear for the next train, and it was normal to clear one's signals again ready for the next one (if it was taking the same route as the previous one), even if he didn't know how much time would pass before it was not far away, until receiving the requisite first bell code from the previous box.
Hence, even in the 1960s, some of the older southern GN main line signalmen still referred to receipt of an 'Is line clear?' bell signal in Absolute or Permissive Block, as "getting the b'ready" (in those old times { 135 years ago! }, 'Be ready' for xxxx train's approach - no need to ask permission; the section was already 'cleared' and the signals 'off').
So main signals could remain in the 'off' ('clear') position for long periods, allowing them to become frozen in extreme winter conditions, not helped by the fact that their arms pivoted in a side-to-side slot through their posts (and I think the official 'clear' indication was with the arm invisible, dropped to vertical inside the post's slot, although many signal arms may not have quite gone down so far in reality).
.... No doubt that accident was instrumental in the subsequent change to 'closed' block, as still in use today, where block sections are considered 'closed' (older 'closed block'-era block instruments often had the appropriate segment of their indications 'dial' labelled as 'LINE CLOSED', rather than the more modern 'NORMAL') until 'opened' for the passage of each train by it being offered by one box to the next and accepted by the signalman there, and so on successively, section by section.
And the type of signal arm/post position and pivot arrangement in use was shown up as capable of improvement, and subsequently led to the invention of the somersault signal (reputedly thanks to a {virtually uncredited} railway clerk at Hitchin deciding to try thinking up a new design), which had the signal arm no longer moving in a slot, the arm pivot point was moved away from the post on to a side bracket, and the arm became centrally pivoted, combating the possibility of snow build-up on the face or back of a then-conventional (and glass spectacle-less {the night-time signal lamp was usually mounted lower down the post}), unequally pivoted arm overpowering its counter-balance weight and risking the arm drooping down when it ought to be at Danger (horizontal).]
'Abbots (at the time I think it would have been Abbotts) Ripton involved frozen signals*, was in the dark, and in laying snow; - I've a feeling it was also during a blizzard.blackout60800 wrote:One of the Flying Scotsman incidents was a head on collision involving thick fog and a frozen signal. Can't remember which one though.
[* - This was when what is sometimes called 'open' block was still in use; i.e., although the signal boxes were in telegraphic communication for signalling trains, as soon as one signalman received 'train out of section' from the box ahead, the status of the block section was regarded as clear for the next train, and it was normal to clear one's signals again ready for the next one (if it was taking the same route as the previous one), even if he didn't know how much time would pass before it was not far away, until receiving the requisite first bell code from the previous box.
Hence, even in the 1960s, some of the older southern GN main line signalmen still referred to receipt of an 'Is line clear?' bell signal in Absolute or Permissive Block, as "getting the b'ready" (in those old times { 135 years ago! }, 'Be ready' for xxxx train's approach - no need to ask permission; the section was already 'cleared' and the signals 'off').
So main signals could remain in the 'off' ('clear') position for long periods, allowing them to become frozen in extreme winter conditions, not helped by the fact that their arms pivoted in a side-to-side slot through their posts (and I think the official 'clear' indication was with the arm invisible, dropped to vertical inside the post's slot, although many signal arms may not have quite gone down so far in reality).
.... No doubt that accident was instrumental in the subsequent change to 'closed' block, as still in use today, where block sections are considered 'closed' (older 'closed block'-era block instruments often had the appropriate segment of their indications 'dial' labelled as 'LINE CLOSED', rather than the more modern 'NORMAL') until 'opened' for the passage of each train by it being offered by one box to the next and accepted by the signalman there, and so on successively, section by section.
And the type of signal arm/post position and pivot arrangement in use was shown up as capable of improvement, and subsequently led to the invention of the somersault signal (reputedly thanks to a {virtually uncredited} railway clerk at Hitchin deciding to try thinking up a new design), which had the signal arm no longer moving in a slot, the arm pivot point was moved away from the post on to a side bracket, and the arm became centrally pivoted, combating the possibility of snow build-up on the face or back of a then-conventional (and glass spectacle-less {the night-time signal lamp was usually mounted lower down the post}), unequally pivoted arm overpowering its counter-balance weight and risking the arm drooping down when it ought to be at Danger (horizontal).]
