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Leaves are surprisingly tricky. Trains mulch them into a hard slippery varnish on the rails, which is then extremely difficult to remove (current best methods i

Leaves are surprisingly tricky. Trains mulch them into a hard slippery varnish on the rails, which is then extremely difficult to remove (current best methods involve industrial lasers). The slippery varnish substantially reduces breaking performance, and increases breaking distances. That in turn means all of your safety margins vanish, and it’s no longer possible to operate trains at full speed, and at normal follow distances. All of that in turn means delays on an individual train basis, but also lower network capacity. Given that most of the UKs commuter rail operates at 80%+ capacity (basically the limit, before minor failures consistently result in catastrophic cascading failures), the result is that leaves on the rails is actually a pretty serious problem that’s tricky to solve.

benj111 4y ago
What about some kind of shovel or air blower to remove the leaves before they compress. I don't deny it's an issue. But it happens every year. It's like having trains that can't run when it rains.
- avianlyric 4y ago
  You would have to equip every train with that system, leaf fall during Autumn in the UK is surprisingly high, so cleaning once a day wouldn't even be close to good enough. Many councils increase their street cleaning 4x just to deal with leaves. Not to mention that wet leaves are surprisingly heavy and sticky, so you might need a pretty complicated system to reliably remove leaves on a train moving at full line speed. At the end of the day, leaves cause issues for about four weeks out of every year. That makes it tricky to justify adding thousands of pounds of specialised equipment to every train, just to deal with four weeks. Of course, you could find a solution to all these things, and have far more reliable trains. But the cost would be high, and it would require our government to actually want reliable public transport. So far, all the evidence suggests our government is only interested in subsiding private vehicles, because public transport "doesn't return a profit".
  - iamtedd 4y ago
    Why not point compressed air at the rails? Edit: D'oh, already suggested up-thread. Rest of my comment still stands. I'm sure even electric trains already have a compressed air system for brakes (though being UK, it might be vacuum). If you really want to get fancy, have a computer vision system looking ahead that will only turn on the air when it sees leaves.
    - benj111 4y ago
      Even a vacuum system would imply pressurised (well at least forced, I'm not sure if there's technically a difference here) air.
  - benj111 4y ago
    4 weeks is aprox 1/12 of a year. A train costs multiple millions of £. So 'thousands' of pounds seems reasonable to keep them running properly for 1/12 of the year. Are leaves heavy and sticky when just fallen? From my experience that seems to be the case when they've been around a while. The whole issue is that the network is running at near capacity. If they're being moved away every hour, it doesn't seem like you'd get that issue. Ultimately it hasn't been done, so in some sense you are correct. I think it's more a case that they can't be bothered, rather than a technical or financial limitation.
    - avianlyric 4y ago
      > Ultimately it hasn't been done, so in some sense you are correct. I think it's more a case that they can't be bothered, rather than a technical or financial limitation. Seems rather uncharitable. Given how much effort various rail companies put into providing a good rail service, seems rather odd that they got to leaves and decided “they can’t be bothered” anymore. I mean why stop there? Why bother running the trains at all? Why bother doing track upgrades or maintenance? There’s 20,000 miles of train track in the UK. At 100mph it would take you 8days to traverse all of it. You would need 200 leaf clearing units running at 100mph 24/7 to clear leaves every hour. I can see why that might be a logistical challenge.

benj111 4y ago

What about some kind of shovel or air blower to remove the leaves before they compress. I don't deny it's an issue. But it happens every year. It's like having trains that can't run when it rains.

avianlyric 4y ago
You would have to equip every train with that system, leaf fall during Autumn in the UK is surprisingly high, so cleaning once a day wouldn't even be close to good enough. Many councils increase their street cleaning 4x just to deal with leaves. Not to mention that wet leaves are surprisingly heavy and sticky, so you might need a pretty complicated system to reliably remove leaves on a train moving at full line speed. At the end of the day, leaves cause issues for about four weeks out of every year. That makes it tricky to justify adding thousands of pounds of specialised equipment to every train, just to deal with four weeks. Of course, you could find a solution to all these things, and have far more reliable trains. But the cost would be high, and it would require our government to actually want reliable public transport. So far, all the evidence suggests our government is only interested in subsiding private vehicles, because public transport "doesn't return a profit".
- iamtedd 4y ago
  Why not point compressed air at the rails? Edit: D'oh, already suggested up-thread. Rest of my comment still stands. I'm sure even electric trains already have a compressed air system for brakes (though being UK, it might be vacuum). If you really want to get fancy, have a computer vision system looking ahead that will only turn on the air when it sees leaves.
  - benj111 4y ago
    Even a vacuum system would imply pressurised (well at least forced, I'm not sure if there's technically a difference here) air.
- benj111 4y ago
  4 weeks is aprox 1/12 of a year. A train costs multiple millions of £. So 'thousands' of pounds seems reasonable to keep them running properly for 1/12 of the year. Are leaves heavy and sticky when just fallen? From my experience that seems to be the case when they've been around a while. The whole issue is that the network is running at near capacity. If they're being moved away every hour, it doesn't seem like you'd get that issue. Ultimately it hasn't been done, so in some sense you are correct. I think it's more a case that they can't be bothered, rather than a technical or financial limitation.
  - avianlyric 4y ago
    > Ultimately it hasn't been done, so in some sense you are correct. I think it's more a case that they can't be bothered, rather than a technical or financial limitation. Seems rather uncharitable. Given how much effort various rail companies put into providing a good rail service, seems rather odd that they got to leaves and decided “they can’t be bothered” anymore. I mean why stop there? Why bother running the trains at all? Why bother doing track upgrades or maintenance? There’s 20,000 miles of train track in the UK. At 100mph it would take you 8days to traverse all of it. You would need 200 leaf clearing units running at 100mph 24/7 to clear leaves every hour. I can see why that might be a logistical challenge.