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A Question About Uk Signalling

Discussion in 'Off Topic' started by Archytoothis, Apr 1, 2021.

  1. Archytoothis

    Archytoothis New Member

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    Good evening all,
    (Apologies for grammar and format, typing this on a phone screen)
    I have a question about UK signalling, more specifically four aspect yellow signals and how drivers react to them. I know it’s not too off topic, but I was hoping somebody who is more knowledgable than I am could shed some light. My understanding goes as far as to what they mean: double yellow - prepare for the next signal to be single yellow, single yellow - prepare for the next signal to be at danger. I read something which would make sense but couldn’t find any actual source. It said they also have speed restrictions attributed to them, ie double yellows - 75 mph, single yellows 45 mph. From the IRL cab rides I have watched I have observed drivers applying brakes when encountering yellow aspects. I was just more curious than anything as to whether this was why or maybe theres’s another more complicated reason?
    Many thanks!
     
  2. solicitr

    solicitr Well-Known Member

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    There are no actual rules: it isn't a speed-signaling system. The driver is expected to know how far it is to the next signal and how much distance at what speed it will take to stop the train he's driving. UK rail depends a lot on memorization.
     
  3. Archytoothis

    Archytoothis New Member

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    Ah I see, the amount of knowledge they have to cram inside and retain must be incredible. Thank you for that!
     
  4. paulc

    paulc Well-Known Member

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    The next signal could be a few hundred yards or 2 miles, route knowledge is key on UK routes.
     
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  5. stijn.claessens

    stijn.claessens Active Member

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    Are there any plans to change this or has it ever been discussed? It seems to be a bit of an outdated method to just rely on memorisation in these modern times.
     
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  6. solicitr

    solicitr Well-Known Member

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    This is a railway system which still treats dynamic brakes as a Popish plot and will ha' nowt to do wi' em.
     
  7. Archytoothis

    Archytoothis New Member

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    Especially at the speeds trains travel at, and the greater number of trains with demand increasing for space and capacity. I’m not sure if it’s a swear word but is *beep*HS2*beep* meant to have speeds faster than 125?
     
  8. solicitr

    solicitr Well-Known Member

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    Yes; but like HS1, it will have some kind of in-cab signaling system.
     
  9. ARuscoe

    ARuscoe Well-Known Member

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    When they were trialling faster running on the UK mainline they introduced flashing green which was supposed to indicate that 125+ speeds were available on that stretch of line, but yep HS2 will be faster than the mainlines and will have in cab signalling
    I believe crossrail has a version of in cab control so they can run trains closer together than would otherwise be possible so it's likely HS2 will have a mixture of both given the speed and separation of the line
     
  10. raretrack

    raretrack Active Member

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    Medium to long term, yes. Network Rail's signalling strategy is to upgrade busier main lines to ETCS (European Train Control System). The southern section of the East Coast Main LIne is planned to be the first mainline to be converted.
     
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  11. raretrack

    raretrack Active Member

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    More generally, when I used to regularly cab ride on the Great Eastern in the 80s and 90s, double yellows were more or less treated as greens! Single yellow meant "hold on to your drinks"!
     
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  12. JJTimothy

    JJTimothy Well-Known Member

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    A dynamic block system is the ultimate in flexibility. Each train effectively defines its own block, or track section, by having its position and speed monitored continually and being kept a safe stopping distance behind the one in front. Of course this necessitates all trains being in contact with a control centre, but that's fairly straightforward these days, and some sort of in cab signalling which is desirable anyway- as trains get faster line side signals get harder to read.

    Electric trains have had dynamic brakes for ages feeding the power generated back into the supply. I admit I don't really see the point of dynamic braking on Diesels- there's no way to reclaim the power which is just dissipated as heat (in development hybrid systems excepted) so why not just use the regular brakes?
     
  13. Archytoothis

    Archytoothis New Member

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    So is it just a classic British stubbornness and reluctance to leave behind the “good old days” that have prevented upgrades from happening already? Or is the fact much of the network is still based on such an old system that it would have been financially impossible.
     
  14. raretrack

    raretrack Active Member

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    No, it is not. British Rail, for instance, invented solid state interlocking (now computer based interlocking) in the 1980s, as a result of a research and development programme. Now standard across the world, it's easy to forget how innovative that was.
    That's closer to the mark. It is not cost-effective to replace signalling until it's near life-expired, and to migrate to something like ETCS requires a critical mass of compatible trains too. The conditions are now right to move towards that, on a much wider scale than hitherto (Cambrian, Thameslink Core and Heathrow Airport branches being the limited examples to date).
     
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  15. solicitr

    solicitr Well-Known Member

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    Regenerative braking (which is what re-feeding the grid is called) is a newfangled eco-thing. Dynamic braking is a means of controlling a train, and has been around since 1939 and the original FT. It is universal- except in the UK - because you cannot hold friction brakes down a long grade with a heavy train without overheating them. I suppose Britain has done without because the UK doesn't have any mountains.
     
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  16. Lamplight

    Lamplight Well-Known Member

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    There are multiple advantages to dynamic brakes on diesels. They‘re quick to apply and release which means that you can easily adjust and fine tune them. As long as their heat dissipation is good enough, they can be continuously applied whereas that would utterly destroy any friction brakes. This makes dynamics brakes especially useful on gradients. In general, the use of dynamic brakes reduces the wear and tear on friction brakes which is part of the reason why blended braking systems (loco uses dynamics while cars/coaches use friction) are so popular.

    Regenerative brakes are a relatively new version of dynamic brakes. Dynamic brakes themselves have existed a lot longer for the outlined reasons. There‘s a good reason why most American diesels have them. There‘s even a lot of electric locos with them (not with regenerative brakes but with regular dynamic brakes with heat dissipation) such as the Br 155 and GE 4/4 for the same reasons.
     
  17. Archytoothis

    Archytoothis New Member

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    That makes sense, thank you!
     
  18. JJTimothy

    JJTimothy Well-Known Member

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    I did conflate the two to be fair though both work by driving the traction motors. Regenerative braking was used on the Woodhead line- an electrification project that began during WW2 though was put on hold for about a decade. I don't know about the Newport electrification of the 1910s.

    There are some hills that make for long inclines though nothing like the Rockies or Alps of course. Perhaps the fact that the main traction on British railways was steam until well into the '50s also has something to do with it. There were a couple of steam turbine-electric prototypes but, apart from them, I can't see how dynamic braking would work with a kettle.

    Forgive my ignorance- FT?
     
  19. solicitr

    solicitr Well-Known Member

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    The FT was the original EMD F-unit, the predecessor of the F3, F7 and F9.

    [​IMG]

    (Incidentally, I stand corrected: the 1939 prototype didn't have dynamic brakes. Those were first installed on the production units, beginning with those delivered to the ATSF in 1940).
     
    Last edited: Apr 3, 2021
  20. raretrack

    raretrack Active Member

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    Regen braking for electric trains was invented in 1886, according to Wikipedia. In the UK it was installed on the MSW route (Woodhead line) when that was electrified in the mid-1950s, although that fed back into other trains rather than back into the grid. On our 25kV AC lines we've fed back into the grid for the last decade or so.

    DOH: just saw the replies above. Should've read 'em before posting ;)
     
  21. Lamplight

    Lamplight Well-Known Member

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    I lost count of how often I wished for dynamic brakes on NTP :D
     
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  22. ARuscoe

    ARuscoe Well-Known Member

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    Britain does have mountains, what it doesn't have are mountain ranges, so we can just build around the higher bits
     
  23. Lightspeed

    Lightspeed Active Member

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    The railways in the U.K. are some ways behind in terms of in-cab signalling, railway infrastructure because the Victorian made rails are outdated by today’s standards. I even think the U.K. is the only country that has no double decker coaches or modern hauled loco services. (Well, apart from the north of England and Scotland where they have class 68 hauled passenger services with a control cab at the end.) I know the we used to have double decker coaches way back in the old days but, turns out they didn’t last long...
     
  24. solicitr

    solicitr Well-Known Member

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    Ironically, the RAF did the future DB an enormous favour by clearing out all that old 19th-century trackage and making them start over.....
     
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  25. ARuscoe

    ARuscoe Well-Known Member

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    We don't have double deckers because of bridge heights on the main routes
    Not sure why loco hauled services are advantageous in the modern era...
     
  26. Phil78

    Phil78 Active Member

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    Because Denzel Washington would have had 54% fewer lines in Unstoppable without dynamic brakes.
     
  27. ARuscoe

    ARuscoe Well-Known Member

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    As others have said, reduced wear on other forms of brakes, better braking over time without fade and even if the energy can't be reclaimed onto the grid, it could be reclaimed and used internally I guess (dunno if it is or if the energy just bleeds off)
     
  28. JJTimothy

    JJTimothy Well-Known Member

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    Given the quality of most of the dialogue in Unstoppable I don't think he'd have minded.
     
  29. JJTimothy

    JJTimothy Well-Known Member

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    Yes the Southern made double deck EMUs which sort of worked- they were more split level really with upper and lower compartments staggered each upper compartment having its own steps down to a lower one for access and egress. I can't imagine it allowed for much greater capacity with all the space needed for stairs and, as someone who is 6'3" and averse to being cramped to the point of claustrophobia, I'd rather ride a Pacer. I can see it being a nightmare to evacuate or access in an emergency.

    The British loading gauge is just too restrictive. The Great Central Railway was built to the Berne loading gauge in anticipation of traffic from the continent via ferries or a proposed Channel Tunnel! Of course the traffic never materialised and the GCR line was one of the most notable closures after the Beeching Report.
     
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  30. stijn.claessens

    stijn.claessens Active Member

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    Oh Doctor beeching, what have you done?
     
  31. Kim1087

    Kim1087 Active Member

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    This signalling guide is from TS2015 but the principle is the same British Signalling Guide
     
    Last edited: Apr 7, 2021
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  32. Kim1087

    Kim1087 Active Member

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