Cooling the trains is a relatively easy problem to solve these days. It’s cooling the tunnels and stations that’s the true engineering challenge.
Once you see it, you can't unsee it. There's this dark mist in the London underground, I find it very visible on the northern line, around elephant and castle. Just standing at one extreme of a platform and trying to look at the farthest part of the station, you'll realise everything is "foggy" by lack of a better term.
One hour there would turn my snot black.
I'm struggling to find a source that tells the reason, but here you can see they chose wooden brakes.
https://www.stm.info/sites/all/modules/custom/stm_import/imp...
By eliminating this heat, they are able to use that heat budget to run air conditioners on the trains and they still make less heat overall. As a side effect, the dust should be reduced too (and probably a bit of the maintenance)
https://www.modernrailways.com/article/revolution-piccadilly....
Same with loudness which on some (old) lines is way past safe.
The most up-to date information on the tube I could found was this report[0], that only covered a number of stations. Even then, the information provided is not great, e.g. for Highbury & Islington:
> The results for particulate matter were between <0.02 and 2.16 mg/m3 for PM2.5.
Results cover the range from 4x of WHO recommended limit (5 μg/m3, i.e. 0.005 mg/m3) to 432x.
[0] https://content.tfl.gov.uk/dust-monitoring-lu-stations.pdf
1. Why is it _so_ hot in the tube? I can understand when the metro in Madrid gets hot, but London?!
2. How many people living in London, and taking the underground regularly, have hearing problems? How can a train be that loud and still be allowed to operate?! I've never experienced a train as loud as on the Victoria line.
tl;dr: when the underground was built, it was very cold down there (14C) to the point where people would go visit the underground in summer just to cool down. So no thought was build in the extra ventilation tunneling for future cooling it since it was already so damn cool.
But over the 100 years since then the trains and people have heated up the tunnels and stations, and since underneath London it's clay, it works as insulation so the heat never manages to dissipate, but rather gets trapped.
There are projects to add cooling to stations, but since they're old, deep, cramped and built in a dense metropolis that is already full of other stuff both above and underground, it is difficult and expensive to do.
It's getting like 1-2 degrees hotter each year
This seems to be a problem almost exclusively on deep tube line escalators, in my experience.
As a software engineer who's not touched hardware design in 25 years, I found this heat budgeting really interesting.
But stations - that's a cost. Stations are connected to the surface by multiple shafts, or are already exposed.
Not correct in context. You cannot successfully chill air without having a place to vent the resulting waste heat.
Where, in deep tube lines, to vent the waste heat, is _not_ a solved problem. It _is_ an unsolved engineering challenge.
The heat has been accumulating there for decades.
As detailed here
https://en.wikipedia.org/wiki/London_Underground_cooling