What if

[JuanMena]

We had roads underground, like subways but for cars.
The cars and their CO2 emissions would get trapped in"the roof" of underground roads and filtered towards patios/green areas to feed trees and plants on the surface.

In that way, CO2 emissions gets recycled, and it justifies having large green areas in highly condensed areas and cities.

 

[CoolMe]

It's not 3am sleep-deprived level rambling yet but, you're getting there

 

[Veho]

Trees are shit at capturing CO2 though.
It should be vented to algae bioreactors that are way more efficient.
And the algae could some day be used to make biofuel so it's win-win.