6 ms·

To be honest, for me the most interesting part of the blog post was this one-liner "for an unbuilt high-speed District line service between South Kensington and

• brainwad 5y ago
  Express services on shared track isn't common on metro systems. NYC's express subways all use dedicated track, for instance. The tendency to not keep to a strict timetable and the close-running of metro systems makes it hard to slot express trains into gaps between local trains properly.
  • traceroute66 5y ago
    > The tendency to not keep to a strict timetable and the close-running of metro systems makes it hard to slot express trains into gaps between local trains properly. To be fair, "close-running" is not a word that tends to be associated with the District line ... "signal failure" is, however ! ;-)
    • Symbiote 5y ago
      The central section (including the Circle Line) has a service interval of 2-2½ minutes, depending on the time of day. The rest has roughly 2-10 minute intervals.
  • zhte415 5y ago
    Trivia. The timetable, or Working Table, for all London Underground train movements is here https://tfl.gov.uk/corporate/publications-and-reports/working-timetables https://tfl.gov.uk/corporate/publications-and-reports/workin...
    • nicoburns 5y ago
      Crazy that the time between trains is measured in seconds
  • marcinzm 5y ago
    Even with a strict timetable you need extra spacing between trains and potentially slowdowns to allow passing to be done properly. These systems on busy lines tend to run trains as close to each other as possible without causing safety issues so there's no buffer room. And if something goes wrong for any reason the whole system starts getting cascading delays.
• s15624 5y ago
  The majority of the tube network is pretty much already at peak capacity, with trains on the Victoria, Jubilee and Northern being full autonomous with moving block systems as separation distance can now only be maintained through autonomous systems. I think an express service would be wonderful but it would require careful orchestration. I think it might be worth increasing the line speed through signaling upgrades and more automation.
  • nicoburns 5y ago
    They are effectively building an express system as seperate lines. E.g. the new Elizabeth line is effectively an express Central line.
  • traceroute66 5y ago
    Isn't the problem with automation on the tube less the technology but more the unions ?
    • lmm 5y ago
      No, it's the technology or perhaps the companies supplying it (unions are only ever a problem in the US - or maybe they're never a problem and there's only a propaganda system against them in the US). London Underground are currently in the process of literally the third attempt to upgrade the signalling on the subsurface lines (i.e. including the District) - the previous attempt by Bombardier failed outright (as London Underground were aware it would from the early days, but they were politically obliged to wait until the company admitted as much), and the one before that (a similar story with New Labour ideology-driven PPP) was also abandoned.
    • lbriner 5y ago
      It is mainly due to an enormous expense and wanting to keep everything running during upgrades. If you are already costing the taxpayer X million per year and then you want another 400M for an upgrade, are you likely to get it?
    • gsnedders 5y ago
      Full automation—without drivers—would typically require platform edge doors, which are expensive and troublesome to introduce without disrupting service, and very difficult on some of the curved platforms. The benefit for the cost involved really just isn't there; while drivers aren't cheap they aren't impossibly expensive in comparison with the average number of passengers per train.
• noneeeed 5y ago
  The only way to have express and stopping trains on the same track is to have frequent passing places. Scheduling and signalling get fiendishly complex. On somewhere like the underground, where building those extra passing places is really hard it just isn't worth it. This is one of the big missunderstandings about the HS2 line. Politicians focus on the shorter journey times, but the big win is actually increased capacity. HS2 will take the express trains off the normal line. With just HS trains on that line you can run more of them than you can if you have stopping trains sharing the track. In addition you should actually be able to run more stopping trains faster since they don't need to be fitted in around the expresses with no extended stops waiting for a delayed express to pass at a station or passing place.
  • adwww 5y ago
    Could you have odd / even trains that miss stops?
    • noneeeed 5y ago
      Yes, you can do things like that, but that ends up with you having two different sets of stations that are not easy to get between. The normal pattern is express trains that stop a few times with stoppers that "fill-in" between, but there will be different patterns of stopping to try and optimise for different groups of travelers. Scheduling/timetabling is a wickedly hard problem, especially in a system like a railway, it's the sort of thing people get Maths and CS PhDs in. The contstraints that you have to solve are complex and interconnected and are part of a bigger network, and you are also trying to please a lot of people with very different (often contradictory) needs.
      • adwww 5y ago
        Yeah I've previously worked on some constraint programming tasks and it was fun but mind-boggling.
        • noneeeed 5y ago
• dspillett 5y ago
  For large parts of London's underground (and overground[†]) it is simply the case that it wasn't really designed — lines were slapped in willy-nilly by disparate commercial interests with relatively little forward planning, and only later became something like a coherent whole with some consideration for coordinated thinking. Once the lines are in, upgrading them is more difficult than building them in the first place, particularly if you don't want to stop service for large parts of the improvement work. > just like in any other number of countries around the world Other cities had extra benefit of hindsight, being able to design around the problems identified in older systems (particularly London's). > They could have used the same rails, no need for a separate line You at least need passing places around stations in practise. In theory* you could have many extra points and pass trains between the existing two lines to work around each other instead of keeping one line dedicated for each direction (as is the case for most of the track length) even at stopping points like stations but that gets complex to manage, has more moving parts (which are difficult to maintain in the confined space), would considerably slow down flow at busy periods as the trains can't move as fast over the points (particularly if they may need to switch line at them) and will spend time waiting for an opposing train ahead to switch out of the way, the tunnel around each change point needs to be wider (for the train partly, unless you redesign them too, for maintenance even more so), … It might work for a small number of non-stop trains worming their way through the system around the majority stop-start services, but that number of services would be so small to the point where the investment would not be nearly worth the small overall gain in reduced journey times. [†] only about 45% of the line distance of the current tube is actually underground[‡] [‡] though that includes large overground sections in the outer zones if you are only considering central London I suspected that %age is considerably higher
  • traceroute66 5y ago
    Thanks for the insight @dspillett, makes sense.
• nickdothutton 5y ago
  One of the things you need to remember when thinking about the London Underground, is that it was a scheme that was ultimately unfinished. There were great plans between the world wars to extend it in size and functionality but ultimately these were all stopped by WW2 and an impoverished UK couldn’t afford to do them afterwards. It was planned to extend the network well into Surrey, Kent and other places.
  • Ichthypresbyter 5y ago
    They also chose not to build many of the suburbs that the extended lines would have served, and instead to keep those areas rural as the Metropolitan Green Belt and to build new towns further away from London.
    • tialaramex 5y ago
      I grew up in the resulting green belt with restricted residential development of Metroland. Of course in practice what happens is that many people who "must" work in the City but have the salaries that come with that, choose to move, especially when they have young families, out to "the countryside" where the Metropolitan Line ends at e.g. Amersham. There you can walk from your house (with a view of woodland and fields across the valley) to a London Underground station (you probably don't actually catch an Underground train, even the express takes too long, you catch a "normal" commuter train serving the same station but these days it's the same price because it's the same system) in the morning and the reverse even evening. And your children grow up away from the noisy polluted city, but not so far away that you can't take them to see a stage show or one of the museums on a whim. Which is nice for them, but hardly screams "sustainable" as a society.
• lbriner 5y ago
  There are not many/any high-frequency metro systems that can do this on the same rails. At peak times, when you could do with the expresses the most, there can be stopping services 1/2 minutes apart on average, which means non-stoppers are simply not possible. On regional railways, where the service might be every 30 minutes or longer, it is a different prospect since you can send the stopper out immediately after the express and it gets 30 miuntes to get out of the way.
• willyt 5y ago
  The tube has shorter times between trains than the New York subway. For example, Picadilly/Central/Victoria line trains run at <120 second headways on the central section. You couldn't control the gaps between trains precisely enough to demerge and remerge trains once you account for random factor of passenger loading and unloading and changing gaps between trains as they accelerate and decelerate between stations. Better to build a whole separate line, in fact this has been done already, the Victoria line is pretty much the express version of the Piccadilly line and likewise Crossrail will be the express version of the Central line.
  • anticensor 5y ago
    > random factor of passenger loading and unloading and changing gaps between trains as they accelerate and decelerate between stations. Solution: Never arrive early, never depart late, and keep the stopping durations fixed, at the longest time possible (which is one quarter the time between the two closest neighbouring stations).
    • Smaug123 5y ago
      That's not actually a solution. What do you do when someone holds the door open? Unless you have someone next to each door ready to boot such people out of the train, you simply can't stop yourself departing late.
      • deleted 5y ago
        [deleted]
      • anticensor 5y ago
        Have station doors, and slam shut them before the train doors close.