I have a friend who lives in an apartment near a major, major artery in Seattle. It's 6 lanes wide looking out from the balcony directly down onto the street. It's what they can afford in a somewhat close commute to work by bus (they can't afford a car). I lived in an apartment a block from I-5 for 6 years. I've made enough money to buy a house in a neighborhood away from traffic pollution. It was a major part of my purchasing decision.

Zoning often puts more dense and therefore cheaper housing near busy roads. I think a lot about who can afford fresh air and who can't, and the compounding impacts of that quite often.