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Comment by walthamstow | Hacker News Reader

London has changed for the better for sure but black snot on the tube hasn't changed at all. I get it from 20 minutes on any deep line like the Victoria. It's from train brake dust, nothing to do with vehicle emissions.

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Victoria might be one of the worst for this. You can hear the wheels screaming the abrasion off for long sections of it. It’ll be interesting to see whether the Piccadilly gets better for you when the new trains arrive over the next couple of years.

I think the screeching is because the section from Highbury to Blackhorse is one massive right hook that the trains take at an uncompromising speed.

The Tube has a real ventilation issue - not just the brake dust, but also temps and staleness. Some of those lines, it’s like a 24/7 sauna!

I think I read that the warmth from people and braking has baked some of the clay earth around the tunnels, making them even more insulative!

Because of how old they are there is some really interesting long term data as the earth itself around the tunnels reaches a new thermal equilibrium. In looking for a source, i found a good wikipedia article on tube temp in general.

These comments and the article made me see how much of it is/was due to braking. TIL.

https://en.wikipedia.org/wiki/London_Underground_cooling

Ha, I happened upon an interesting video earlier today on this topic! https://youtu.be/4MzHt_YLnjw

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