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Underrated comment. For those not from the UK, "leaves on the line" is their #1 excuse for late-running trains.

by llimos 6y ago

noneeeed 6y ago
For those that are wondering why leaves would cause trains to be late, Network Rail have a good lay-persons summary of the problem https://www.networkrail.co.uk/running-the-railway/looking-after-the-railway/delays-explained/leaves/ https://www.networkrail.co.uk/running-the-railway/looking-af... The short answer is that leaves crushed under train wheels make for a very slippery layer that makes it hard to brake and can affect some of the train location tech (axel counters). This post has some nice info about some research into why some leaves seem to be more of a problem than others, and also the measures used to try and clean the track.
- iggldiggl 6y ago
  > can affect some of the train location tech (axel counters). Er, I think you mean track circuits, don't you? Those work by virtue of the train's wheels and axles creating an electrical connection between the two running rails, and would therefore indeed be likely to be affected by a potentially isolating layer of leaves on the line. Axle counters on the other hand just detect the wheels by other means (usually contactless by magnetic or inductive sensing), so wouldn't be affected by the presence of leaves. Again the UK is more susceptible to problems in this regard because it's been almost exclusively using track circuits for train detection until comparatively recently – it's only in the last two decades that axle counters have started seeing more widespread usage.
  - noneeeed 6y ago
    Yep, I got myself mixed up. It's been 15 years since I worked in thebrail industry, so I'm a bit rusty.
tialaramex 6y ago
Culturally this is the common excuse. So if you're making a situation comedy, you might have a character announce this is why they're late, and then maybe another character observes that it's currently May (The UK is in the Northern Hemisphere and so leaf fall is associated with autumn and early winter in maybe October through December) In practice this is not actually a very common cause of unanticipated delay, although it can happen. Where deciduous trees (the kind with annual leaf fall) grow over or very near to railway lines, leaves may accumulate on the rail and will be crushed by the tremendous weight of the train, this creates a potentially very low friction layer on the rail, which makes braking difficult, leading to problems with the train service. Of course both the most trivial (don't have so many deciduous trees in places where that's a problem; re-schedule trains during leaf fall to allow for worse braking) and sophisticated (fit special equipment to trains to destroy the leaves) solutions are in use to reduce the likelihood of this happening. Because leaves don't seem like a big threat to a bipedal human the juxtaposition (seemingly unthreatening leaves actually causes big problems) is good comedy. The actual most common reason announced is "Signal failure". This too is misleading and an opportunity for comedy, since it might seem as though it refers to e.g. an incandescent bulb burned out in a signal lamp - why not just fit two or use LEDs (they do). But in reality "signal failure" means any part of the entire signal system, including every sensor and component, might have failed and as a result the system has degraded working. For example perhaps in one of the sixteen motorised points ("switches" in US terminology) at a busy junction a sensor that confirms the metal "lock" to prevent undesired movement is in place has broken and its output is floating instead of tied. A human needs to go there, stop any trains nearby, take the machine to pieces, replace the sensor, put it all back, confirm it works, and then re-open, until then that part of the junction mustn't be used because the computer isn't sure it's safe, and all resulting delays will be reported as "Signal failure".
- codeulike 6y ago
  "The wrong type of snow" is another famous one https://en.wikipedia.org/wiki/The_wrong_type_of_snow https://en.wikipedia.org/wiki/The_wrong_type_of_snow

Underrated comment. For those not from the UK, "leaves on the line" is their #1 excuse for late-running trains.

by llimos 6y ago

Underrated comment. For those not from the UK, "leaves on the line" is their #1 excuse for late-running trains.

For those that are wondering why leaves would cause trains to be late, Network Rail have a good lay-persons summary of the problem https://www.networkrail.co.uk/running-the-railway/looking-after-the-railway/delays-explained/leaves/ https://www.networkrail.co.uk/running-the-railway/looking-af... The short answer is that leaves crushed under train wheels make for a very slippery layer that makes it hard to brake and can affect some of the train location tech (axel counters). This post has some nice info about some research into why some leaves seem to be more of a problem than others, and also the measures used to try and clean the track.

iggldiggl 6y ago
> can affect some of the train location tech (axel counters). Er, I think you mean track circuits, don't you? Those work by virtue of the train's wheels and axles creating an electrical connection between the two running rails, and would therefore indeed be likely to be affected by a potentially isolating layer of leaves on the line. Axle counters on the other hand just detect the wheels by other means (usually contactless by magnetic or inductive sensing), so wouldn't be affected by the presence of leaves. Again the UK is more susceptible to problems in this regard because it's been almost exclusively using track circuits for train detection until comparatively recently – it's only in the last two decades that axle counters have started seeing more widespread usage.
- noneeeed 6y ago
  Yep, I got myself mixed up. It's been 15 years since I worked in thebrail industry, so I'm a bit rusty.

tialaramex 6y ago

Culturally this is the common excuse. So if you're making a situation comedy, you might have a character announce this is why they're late, and then maybe another character observes that it's currently May (The UK is in the Northern Hemisphere and so leaf fall is associated with autumn and early winter in maybe October through December) In practice this is not actually a very common cause of unanticipated delay, although it can happen. Where deciduous trees (the kind with annual leaf fall) grow over or very near to railway lines, leaves may accumulate on the rail and will be crushed by the tremendous weight of the train, this creates a potentially very low friction layer on the rail, which makes braking difficult, leading to problems with the train service. Of course both the most trivial (don't have so many deciduous trees in places where that's a problem; re-schedule trains during leaf fall to allow for worse braking) and sophisticated (fit special equipment to trains to destroy the leaves) solutions are in use to reduce the likelihood of this happening. Because leaves don't seem like a big threat to a bipedal human the juxtaposition (seemingly unthreatening leaves actually causes big problems) is good comedy. The actual most common reason announced is "Signal failure". This too is misleading and an opportunity for comedy, since it might seem as though it refers to e.g. an incandescent bulb burned out in a signal lamp - why not just fit two or use LEDs (they do). But in reality "signal failure" means any part of the entire signal system, including every sensor and component, might have failed and as a result the system has degraded working. For example perhaps in one of the sixteen motorised points ("switches" in US terminology) at a busy junction a sensor that confirms the metal "lock" to prevent undesired movement is in place has broken and its output is floating instead of tied. A human needs to go there, stop any trains nearby, take the machine to pieces, replace the sensor, put it all back, confirm it works, and then re-open, until then that part of the junction mustn't be used because the computer isn't sure it's safe, and all resulting delays will be reported as "Signal failure".

codeulike 6y ago
"The wrong type of snow" is another famous one https://en.wikipedia.org/wiki/The_wrong_type_of_snow https://en.wikipedia.org/wiki/The_wrong_type_of_snow