Two-Aspect Signalling...

Discussion in 'Infrastructure & Stations' started by randompilgrim, 30 Nov 2008.

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  1. randompilgrim

    randompilgrim Member

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    At my local station (devonport(GWML)) there are two signals, Platform one has a two-aspect signal and platform two has only one. The signal on platform two changes between red, yellow and green but i was wondering why it had only one, for example it couldn't show double yellow...

    And also, does anyone know of the exact meanings/rulings for drivers when they see the colours on the signals, for example double yellow.

    Cheers
     
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  3. driver9000

    driver9000 Established Member

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    Hi.

    It sounds like the signal on platform 2 is one of the new LED signals that only require one lens to show all three aspects. Four aspect signalling isnt always used, three aspects being just as common, in three aspect signalling the sequence is Green-Yellow-Red and in four aspects Green-Two Yellow-One Yellow-Red. I sure one of the S&T experts on here can go into detail on how its decided on where gets 3 aspects and where gets 4 aspects.

    Regarding the rules for drivers observing signals. Green indicates that the next signal is displaying a proceed aspect, the driver will receive a bell sound on the AWS in the cab. Two-Yellow (Prelimenary caution) indicates that the next signal is currently displaying One-Yellow, and the driver should regulate his speed accordingly, the driver will receive a warning horn on the AWS and must press a reset button to cancel the warning to prevent the brakes being applied and the train stopped. One-Yellow indicates the next signal is at Danger (Red) the driver will now be braking in order to bring his train to a stand at the Red signal, again the driver will receive a warning horn on the AWS as he did for Two-Yellows. Red (Danger) indicates the driver MUST stop at the signal - simple as that! AWS warning horn will be received as for the caution signals. AWS warnings are given by a fixed magnet approx. 200yds before (in rear) of the signal.
     
  4. Metroland

    Metroland Established Member

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    Double Yellow: Preliminary caution, be ready to find the next signal at Yellow.

    Yellow: Caution, be ready to find the next signal at Red.

    Red: Danger/Stop. Do not pass the signal without permission or unless the rules allow.

    Green: Line clear, at least the next signal section you can proceed at line speed/max train speed.


    4 Aspect signalling, the braking distance is between Double Yellow and Red. Signals tend to be ¾ mile apart, depending on gradient/line speed. High speed/highly trafficked lines.

    3 Aspect signalling, the braking distance is between yellow and red. The signals tend to be just over 1 mile apart, depending on gradient/line speed. Most main lines that do not need closely spaced signals because of traffic loads.

    2 Aspect signalling, the braking distance is again, between yellow and red. The yellow (repeater) and red tend to be the same distance as 3 aspect signals apart. However, the red (stop signals) can be any distance apart in theory. Typically lines signalled this way (Devon banks, Oxford-Banbury, south of Norwich) have stop signals 2-4 miles apart. Lighter trafficked lines – though some lines that were signalled like this now have heavy traffic (eg Banbury-Oxford)

    Going onto Devonport:

    Area is controlled by Plymouth PSB. Typically between the Tamar Bridge and Plymouth it is 3 aspect because of the higher traffic loading/stopping stations. West of the Tamer is 2 aspect and absolute block signalling with semaphores. This reflects the relatively light traffic load.

    Over the Devon banks (Plymouth-Totnes) it is 2 aspect signalling, again, reflecting the relatively light traffic load. That said the line is busier with passenger traffic now than in the early 1970s when it was done. Most of the stop signals replaced former semaphore boxes.

    Totnes-Taunton is mostly 3 aspect,. But there is some 4 aspect and 2 aspect sections, reflecting the traffic loads. Berks and hants (Taunton-Reading) is 2 aspect west of Castle Cary (note this is a 110mph line!) and 3 aspect elsewhere. Reading – London is 4 Aspect.

    One of the signals at Devonport sounds like a new LED search light 3 aspect signals.

    There were a great deal of searchlight signals about years ago – the east coast main line had a good deal of them in the 1930s for example, but then fell out of favour as they were electro-mechanical. The new ones, however, are not, and work on LEDs.
     
  5. JonG

    JonG Member

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    At Devonport, the signal on the down platform (1), sig. P60, is a four-aspect twin LED. The one on the up platform (2), sig. P13, is a three-aspect single LED.
     
  6. O L Leigh

    O L Leigh Established Member

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    I'm glad you guys are around. It's saved me from typing out a long and ultimately speculative reply based on LED signals and the differences between 3 and 4 aspect signalling.

    O L Leigh
     
  7. AlexS

    AlexS Established Member

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    You get 4 aspects with higher speed running or in areas where maintaining the flow of traffic is essential EG New Street approaches - green on a 4 aspect signal means that the next 3 signals including that one are showing proceed aspects - at the minimum Green - Double Yellow - Yellow - Red.
     
  8. GB

    GB Established Member

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    Of course as far as signalling sequences go, in areas of small signalling blocks you could also have G>YY>YY>Y>R or G>YY>Y>Y>R

    Regarding Searchlight siganls, there is still a few about on the GE line North of Marks Tey and on the Clacton/Waton branch. However these will soon be replaced, so hopefully they wont play havoc with TPWS equipment like they currently do!
     
  9. ungreat

    ungreat Member

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    We have 2 aspect SIGNALS on our four aspect SYSTEM.

    All because a signal has just two lights doesnt mean its a two aspect(basically colour light semaphore,Home ,distant,home ,distant) SYSTEM

    Example..three(I think) signals on the approach to Peterborough from London have just two light ports...they are still capable of showing 4 different aspects..red,one yellow,two yellows,green..thus being a 4 aspect signal,despite having only two lenses
     
  10. Chilled Phill

    Chilled Phill Member

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    All Double Lens/Four Aspect where I live. Considering the size of the station, there is a total of six signals in, or at least near, the station itself. :|
     
  11. EE Type 3

    EE Type 3 Established Member

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    Thank god I live in semaphore heaven :lol:8-)
     
  12. TheSlash

    TheSlash Established Member

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    Yeah but don't forget Shunt Ahead, Entering a non passenger line, running dummies {Western and Southern}, erm, yellow discs, erm anymore? :lol:
     
  13. AlexS

    AlexS Established Member

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    Calling on arm, Warning arm (although I think the only one remaining anywhere is Rothley GCR now), Upper/Lower Quad, Fixed distants, coacting signals, slotted signals and so forth.
     
    Last edited: 10 Dec 2008
  14. ungreat

    ungreat Member

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    There's one of of those approaching Sandy on the down slow..it's colour light but the principle is the same
     
  15. metrocammel

    metrocammel Member

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    Regarding to the searchlights still in use around Colchester- Clacton, does anybody know when this area went over to colour-light operation? I seem to think it was the 1950s, but the Searchlight's obviously date back to the earlier part of the 20th C.
     
  16. Metroland

    Metroland Established Member

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    Possibly the 1930s, but more likely just after the war when it was electrified.

    The ECML has quite a few colour light signals fitted at this stage (mostly searchlight). King's cross itself was resignalled in the 30s, controlled from a miniature lever frame.

    In 1939, there were electrically controlled colour-light signals and turnouts at Digswell, controlled by Welwyn North, Leys, near Abbots Ripton. Plus automatic/semi automatic colour lights at:

    Greenwood and Potters bar (Ganwick and North of Potters bar tunnel)
    Potters bar station and Marshmoor (Hawkshead autos)

    Potters bar had a new PSB in the early 50s, controlling the new widened section between Greenwood and Potters bar. This was replaced in the 1970s by Kings Cross PSB.

    Stevenage North and Hitchin South (Wymmondley autos)
    Tempsford Station and St Neots Station (Barford)
    Holme Station and Yaxley fen (Stilton Fen autos)
    Essendine North and Little Bytham Station (Monkswood autos)
    Little Bytham Station and Corby Glen Station (Counthorpe autos)
    Burton down lines only - worked by Corby Glen SB
    Great Ponton and Grantham South (Salterford - down loop controlled by Grantham South)
    Grantham North and Barkston South (Peascliffe autos)
    Crow Park Station and Egmanton (Weston Bank)
    Scrooby and Egmanton (Down only)
    Bawtry Station and Rossington (Pipers Wood autos)

    All of these were controlled (or monitored!) by existing lever framed boxes, leaving a mixture of lattice post LNER signals and GNR somersaults.

    Doncaster was resignalled in 1947, with some colour lights round the station, controlled by an OCR panel. Replaced by Doncaster PSB in late 70s/early 80s.

    York station was resignalled in the early 1950s, controlled by a large OCR panel, at the time the largest in the world

    In the 1930s and during the war, when the line north of York was widened to 4 tracks, searchlight signals installed, mostly automatic and approach lit light many signals installed at the time (because of lack of local power supply, meant batteries were used). These replaced automatic semaphore signals - the NER Halls automatics - installed in 1906. New OCR panels were installed at Thirsk and Northallerton. Northallerton Box opened the day WWII broke out.

    All replaced by York IECC in around 1988/9

    There were also colour light signals in the Darlington area, and around Durham.

    Newcastle was also resignalled in the 1950s with colour light search light signals, controlled by a large OCR panel - replaced by Tyneside IECC 1990

    Edinburgh had minature lever frames with colour lights, not sure when that was done - probably 30s, until replacement in the 70s.

    Most of the re-signalling was done in the 1930s for the higher speed 'streamliners' like Silver Jubilee etc

    More signal box diagrams taken from the 50s/60s can be seen here

    http://richard2890.fotopic.net/c710126.html

    and a plan of the ECML to Doncaster can be seen here

    http://richard2890.fotopic.net/p54468843.html
    http://richard2890.fotopic.net/p54469138.html
    http://richard2890.fotopic.net/p54469139.html
    http://richard2890.fotopic.net/p54469140.html
    http://richard2890.fotopic.net/p54469141.html

    There is also a good diagram of the line between Hitchin and Peterborough here

    http://www.railwaysarchive.co.uk/documents/MoT_Connington1961.pdf

    there is also a few of the signalling notices here

    http://www.signallingnotices.org.uk/notices.php?seq=27
     
    Last edited: 11 Dec 2008
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