Also worth noting that with modern emissions standards (and transition to EVs), over 50% of handful particulates come from tires, brakes, road surface wear, and resuspended dust:
I don't think there's any healthy level of private cars coexisting with humans in a city, without even considering the more immediate harms from crashes, etc.
https://www.oecd.org/en/publications/non-exhaust-particulate...
I don't think there's any healthy level of private cars coexisting with humans in a city, without even considering the more immediate harms from crashes, etc.