The issue boils down to roads and parking more than cars. Trees need sunlight, but cars don’t so roads work just fine segregated below street level away from pedestrians and inclement weather. It sounds expensive, but work out how expensive NYC’s above ground road network costs both in terms of land value and ongoing property taxes and you see just how pricy cheap roads end up.

Go 3D to segregate N/S traffic from E/W traffic thereby eliminating traffic lights and things really pick up. Of course it’s much easier to blame cars, but counties only have so many people you can actually build enough infrastructure to solve the root issues.