[philjohn]

most subway trains are decades old - newer fleets have regenerative braking[1]

But also ... almost a century of brake dust because nobody is going through and vacuuming the tunnels.

[1] https://tfl.gov.uk/corporate/transparency/freedom-of-informa...

[cogman10]

Interesting. Looks like it the line isn't able to take the energy (I'm guessing voltage is already too high) they dump the energy into a resistive heater.

Makes sense, it's just going to be heat anyways. I wonder how often that happens vs the energy getting dumped into the line.