How much cleaner have they gotten, and how much more miles do these factories get driven? Taking a look at https://www.bts.gov/content/us-vehicle-miles (the first useful result I could find), highway vehicle miles have almost tripled since the 1970s (1.1 trillion miles in 1970 vs 3.2 in 2019). Have cars gotten 70% cleaner in the same timespan?
It's not about miles driven. It's about air quality in cities.
Just looking at efficiency, we see that people get 50% more miles per gallon today than in 1978. This doesn't even include impact from emmissions equipment, electric/hybrid cars, etc. Plus, most highway miles are not in cities. Pollutants can disperse and settle out (not ideal in general, but relevant to air quality it is positive). They also have lower densities of people in the area to affect, which should affect the overall population numbers less.
According to the EPA, cars (and trucks and busses) are 99% cleaner today than in the 70s.
