Hacker News Reader

Comment by colechristensen | Hacker News Reader

Wouldn't a powerful fan or a small spinning brush be mostly as good and much cheaper and simpler to deploy?

This is what I was also initially thinking, but after a bit of reading [1] I quickly learned that the actual problem is not some leafs neatly sitting on top of the rails but leafs being turned into a wet grime [2] that gets worked into the surface and makes the rails really slippery. Other candidate solutions for the problem are plasma and laser treatments, so I think they considered using fans and brushes before. The problem is probably closer to removing oil stains from concrete than blowing leafs off the lawn.

[1] https://www.railengineer.co.uk/cleaning-the-rail-head/

[2] Non-native speaker, not sure if that is the proper term.

Great link, more informative (even if not so newsy) than the submission IMO.

And that's a fine term for it.

Yah, its pretty clear from those pictures its not the leaf but the resulting compressed pulp, which looks pretty similar to the stuff I spray off my driveway every year with a 3200psi pressure washer. That i largly a mix of leaf/etc with black mold, which actually grows into the concrete pores.

Which makes me wonder why no one bothered to try something like that, are pressure washers common in the UK? Mine is hardly the highest PSI, and it frequently needs to be turned down because at that pressure it can actually etch soft concrete. And at 2.5GPM its not using a lot of water either.

Pressure washers are the current solution to this problem. Here's a news article about the LIRR switching from a 4000 PSI pressure washer to a 20000 PSI pressure washer: https://www.amodernli.com/lirr-launches-new-tech-to-fight-le... (From 3 years ago.)

The problem isn't just a bunch of leaves, it's the pulp that gets generated by a layer of leaves that gets run over by heavy trains several times an hour. That pulp is particularly difficult to remove.

There are existing solutions for this, of course. For example, the Dutch railways deploy a mush of sand, potato fibers and iron particles on top of the mush to give trains the necessary grip when they brake while they take the caked on goop with them at the same time. This solution can be applied by separate trains running at relatively high speeds.

This approach, like the novel CO2 approach, has advantages and disadvantages, but it should be clear that "just attach a fan and a brush to the front" isn't going to cut it. You'd need a hell of a fan to blow sticky mush off the tracks at 60-65mph (average UK train speeds).

> For example, the Dutch railways deploy a mush of sand, potato fibers and iron particles on top of the mush to give trains the necessary grip when they brake

That sounds like Sandite, which is definitively in use on the UK rail network. But I think the cleaning effect of that is still relatively limited, and the adhesion improvement only lasts a certain number of trains, after which the material needs to be re-applied again to the track.

Thanks for this explanation. The article didn't do a good job at explaining why leaves were such a problem -- it just repeated that it was a big problem. Maybe it should have been obvious but it definitely wasn't to me!

But why is a brush/blade on _every train_ not good enough? Remove the leaves before they turn into a sticky pulp?

Trains run over a stupendous amount of debris. A more involved mechanical solution would just break more.

If a simple mechanical solution worked they'd have implemented it a century ago.

I'd think the brush would muck up

Ok so use a piece of metal?

I really really don't understand how leaves are an issue with trains.

Anyone know why they can't just use a cowcatcher like device?

https://www.forbes.com/sites/lauriewinkless/2021/10/27/why-l...

It's not leaves on the line that are in a pile, it's leaves on the line that get smashed onto the rail, and make the already low friction rails even lower friction. If you can't stop and you can't go, then the railroad isn't going to take you anywhere.

I'm guessing not all of the tracks are welded rails and so they have expansion joints, which means a cow catcher like device trying to scrape a rail clean might hang up on a joint and get destroyed. Plus it would wear down quickly with the metal on metal contact.

The problem isn't necessarily the leaves but the cellulose that's driven out of the leaf and onto the steel rail when it's run over. Additionally, the steel wheels of a train get really hot and probably turn the cellulose (and whatever else is in a tree leaf) into a pretty hard to deal with substance that coats the rail and (likely) the wheel. That makes braking difficult and can probably contribute to safety problems.

It's the sticky crap - sap, cellulose, sugars, plant fats. This can fix larger debris in place, accelerating pitting and weathering of the rail. The co2 pellets freeze the sticky crap, which then gets shattered and dispersed, leaving clean bare metal behind. A scraper or brush would leave nasty residue.

Reply on news.ycombinator.com