How many cars, how much they are driven and how they are driven, depend on urban development.
Urban development -> cars -> pollution
If you want less cars going around, design your cities to allow and incentivize people not to use them. See recent developments in Paris as an example:
https://www.nbcnews.com/science/environment/paris-olympics-city-reduce-air-pollution-rcna153470
^ this: people always scared of being assaulted, never for a collision. Numbers speak clearly