I can understand that cooling a tunnel network like that is difficult, but surely filtering particles from the air is a solvable problem? Movable air filters on the platforms, etc.
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