We can do a lot that would help. We can build electric mass transit (trains, street cars, busses). We can legally mandate that roads have large sidewalks / bike lanes and limit the size of rods. We could remove stroads completely. With how often roads go under maintenance, those rules would be able to be implemented fairly quickly. Remove zoning restrictions that limit density, or make artificial space like setback requirements and parking requirements, then let infill development do the work.

There is a lot that can be done with the stroke of a pen and will be fixed naturally over time.