How does Network Rail work out max speeds?

Discussion in 'Infrastructure & Stations' started by markymark2000, 26 Nov 2019.

  1. LNW-GW Joint

    LNW-GW Joint Veteran Member

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    The location is allegedly over the Weaver viaduct west of Northwich station, a half-mile stretch of 20mph which supposedly could be higher.
    Pacers will be gone shortly, of course.
     
  2. The Planner

    The Planner Established Member

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    That applies to all traffic though if it is the one between Northwich and Hartford.
     
  3. carriageline

    carriageline Established Member

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    Interested to know where your talking about?

    Cannon st as an example was reduced to 15 when it was recontrolled. Most of that was because of the really short overlaps are non compliant now, and resignalling it would destroy capacity with modern standards!

    When checked *apparently* most trains were only doing 15 when it was 20 anyway. Whether that means trains now don10 instead I don’t know!
     
  4. thenorthern

    thenorthern Established Member

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    I think it was something to do with a curve near Northwich.
     
  5. Llama

    Llama Established Member

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    There are no other restrictions on curvature due to Pacers as far as I am aware, is that an urban myth?

    Only other reasons I can think that Pacers might have specific restrictions might perhaps be due to lateral effects of strong winds or due to possible adhesion issues on a steep rising gradient if only one engine out of two is providing traction power.
     
  6. ComUtoR

    ComUtoR Established Member

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    Kidbrooke Tunnel. No changes to the track, layout or otherwise. When it got resignalleded and controlled to the Great Beast TBROC the only change was the CA on UP. The previous 60mph PSR change in the tunnel has been removed and the 20 is now all the way out (on the down) !$£%$"%$%^£$ !!! +1 into Kidbrooke !

    Charlton resignalling has had the PSR boards moved to the signal posts; which alters the speeds somewhat. They tidied up Greenwich which was nice; but on a technicality, the 60, albeit stoopid, was removed. The speed into College Tunnel has been reduced and now I'm so far under linespeed, I'm late into Greenwich all the time. Again, no real changes to anything just a speed reduction for no 'visible' reason.

    I've noticed that the Hither Green resignalling is also pushing some of the PSR boards to the Signal posts (is this the future of PSR placement ?)

    I understand the need to comply with new standards. Cannon has always been a slow crawl into London Bridge. Signal sighting is a drama lama and its highly congested so your always checked in both directions.

    Speed wise, I'm not sure where I stand. As per the Charlton resignalling, it was good to finally get rid of some of those PSRs that were impossible to achieve but on the flip side when its reduced you are limited. I think I'd like to have PSRs that I can't achieve but ones I can push where I can and not worry about my speed.

    Cannon could be 30 all the way out and you would still not achieve it and drive to whatever you were signalled. Getting Greens out (LOLOLOLOL) is a drag at 15mph and your almost touching London Bridge so the 20 PSR change is now kinda pointless. You can get 20 without thinking and previously your only limit was the signals. I'd rather have 20 all the way and drive accordingly.

    Orpington (Ashford box) had another reduction. Country end crossover dropped from 60 to 50. The entire crossover was relaid and it much smoother and I think they also smoothed the curve out a touch. I can't understand why they dropped it to 50. Granted going over it at 60 was a touch scary.

    If the infrastructure can take it, why can't we just have the fastest PSR ? (Yes Mr B Rick, I understand the 80 reasons....)
     
  7. Bald Rick

    Bald Rick Established Member

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    That could only be for axle load. Any locomotive has a higher axleload. So it can’t just be for pacers.

    in which case it would apply to everything.
     
  8. Bald Rick

    Bald Rick Established Member

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    The simple answer is that infrastructure can’t take it. Although I can understand how it can look odd that one day the infrastructure is capable, and the next it isn’t. All the issues you describe as having changed at resignalling will be due to applying signalling standards. For Kidbrooke, I think there’s a standard which prohibits changes of speed inside tunnels - perhaps @MarkyT can confirm. It would have had grandfather rights from the 70s resignalling, but they don’t apply after modern resignalling.
     
  9. 6Gman

    6Gman Established Member

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    I'd be curious to see where a 5mph increase could deliver "big time savings".
     
  10. The Planner

    The Planner Established Member

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    Independent lines round the back of Crewe, would get you a few minutes for freight.
     
  11. 6Gman

    6Gman Established Member

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    Not sure speeding up boxes to Widnes was what the OP had in mind though ... ;)
     
  12. ComUtoR

    ComUtoR Established Member

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    If that is the case then you need to be aware of how much I love you right now. ♥♥♥♥♥♥♥♥♥♥♥ It's been bugging me since it changed. Meeting new standards is what I normally resign new changes too but it takes a few months of frustration to accept it. We have another tunnel where the speed changes. That has a 90mph speed change. I'd hate to see that go.

    Cheers BR.
     
  13. Jimathy

    Jimathy Member

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    How much would I like to travel at a decent speed on the independents. It takes soooooo long, you wouldn't believe!
     
  14. The Planner

    The Planner Established Member

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    If it means I can get an Intermodal out quicker it makes a big difference!
     
  15. Mintona

    Mintona Established Member

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    Does anyone know if the maximum speed through Alderton Tunnel is going to go up from 110 to 125 now HSTs are no longer in use along that section?
     
  16. Wychwood93

    Wychwood93 Member

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    That would be useful - I have often wondered why the 110 PSR is there. Perhaps not suitable for 125 if two trains passing each other there, perhaps HST related, as Mintona mentions.

    Edit: Further to the above - only 30 chains at 110 with 125 either side - from 97m 30ch to 97m 60ch. Sourced from the Sectional Appendix.
     
    Last edited: 28 Nov 2019
  17. Bald Rick

    Bald Rick Established Member

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    I have never known a signed speed restriction for a tunnel to be one class of rolling stock specific.

    It’s almost certainly down to the pressure effect of two trains passing in the tunnel, track substructure (notoriously difficult in tunnels) or structure gauge (unlikely).
     
  18. Mintona

    Mintona Established Member

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    It was the first one, the pressure of two trains passing caused the HST toilets to blow everything back into the cubicle and the speed was lowered to 110 to compensate for this. But IETs with their CET tanks won’t have the same problem so the speed limit could now be removed I’d have thought.
     
  19. Joseph_Locke

    Joseph_Locke Established Member

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    EPS, though technically it applies to 221 and 390, but its close to one class!
     
  20. Bald Rick

    Bald Rick Established Member

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    But that’s not HST specific. It’s trains above 110mph specific (without retention toilets).

    Pedantic I know, sorry!
     
  21. carriageline

    carriageline Established Member

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    I’ll do some digging some digging around all these points mate, and see if I can get some reasons behind them!
     
  22. matacaster

    matacaster Member

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    One suspects that the speed limits are generally very conservative. The reason being that, should an accident happen and speed be an issue, then the person or persons responsible for setting the speed limit too high will get the blame. Despite the introduction of many improvements - better braking, visibility, warning systems, signalling, trackwork, speed on many lines has not increased very much, if at all.

    eg Settle-Carlisle

    -steam days
    vacuum braking, poor visibility from cab, semaphore signalling (no TPWS), low-weight
    bullhead rail, no speedometer. Trains reaching up to 90mph on downhill sections.

    A very small number of accidents over the years, none of which, from memory, related to speed

    -now
    All above improved immeasurably 60MPH max speed.
     
  23. markymark2000

    markymark2000 Member

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    Speed improvements for freight means it gets to it's destination quicker and consequently, more businesses are likely to take up rail freight as a viable option with it being quicker.

    Speed improvements to passenger trains are slightly more important but any speed increase would be welcome.

    We can't increase speeds massively in most cases but any speed increase is a decrease in journey times, whether it be seconds or minutes.

    If a speed can safely be increased without any major works, it should be done. More needs to be done as well to see where speed improvements can be made. There must be a practical way to test for possible improvements like having a train and driver go +5 mph (ECS and have technicians onboard and only on sections which are very low risk for derailments or damage to be caused) and if comfort is still acceptable, no damage caused and safety from a drivers perspective isn't compromised, the speed limit could be increased.
     
  24. ComUtoR

    ComUtoR Established Member

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    A little rose tint to that I think.

    Eltham Well Hall, Morpeth, Salisbury, Grantham, Shrewsbury.

    A lot has changed since the days of steam. Even in recent years the stories some of our 'old boys' will tell you would make you shiver.

    On topic. 'Improvements' to signalling standards do appear to come with lower speeds. I do wonder if the priority is faster or safer. They do go hand in hand but there has to be some drive towards capacity increases too.
     
  25. Bald Rick

    Bald Rick Established Member

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    But, as explained repeatedly, it’s not all about engineering and how quickly a train can go. There are several operational risk factors that have nothing to do with passenger comfort. Level crossing risk for example. Level crossing sighting. Level crossing strike ins. Signal overrun risk. Signal sighting. Positions of safety for the workforce. Passenger safety at platforms.
     
  26. markymark2000

    markymark2000 Member

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    That is why I said, have an ECS train do it at night with technicians etc and only do it where the risk is relatively low. Signal and LC sightings and over run risk would be worked out in this trial. Speed restrictions specifically for LCs, obviously they wouldn't be changed. The point is there are areas which no level crossings (or if there is any, they are ones where you call the signaller). Signals could be an issue but then the tests and trials would show what would need to be sorted (if anything) for a small speed increase.

    Safety for workforce and passengers on platforms is more complex.
     
  27. ComUtoR

    ComUtoR Established Member

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    I've blown a few speeds in my years. Sometimes it can't be helped. I've even been asked to deliberately blow an ESR to test for comfort and operational issues...

    What you need to allow for is that once, isn't usually an issue. Going +5 every single day, multiple times a day could be a potential issue. A single test train isn't a proper stress test. There needs to be some kind of engineering allowance or limits of tolerance. I would assume that this is one of those 80 reasons.
     
  28. Bald Rick

    Bald Rick Established Member

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    A very common mistake. Much of the railway is effectively at (or near) capacity, such that an increase in line speeds just means that the fast trains catch up the stopping trains earlier, and there is no journey time improvement.
     
  29. Bald Rick

    Bald Rick Established Member

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    It’s all more complex. A lot more complex. I assume you haven’t actually done his for real. I have, many many times.
     
  30. Bald Rick

    Bald Rick Established Member

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    There’s tolerance within all the factors, in one form of another. Take underbridge strength for example. It may be fit for 80mph. It will also be fit for 85mph, but with a smaller tolerance above that. However repeated use at 85 instead of 80 will mean an increased risk of that bridge failing suddenly, and a certainty that the bridge will become life expired ealier than planned.
     

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