Making traffic three dimensional is going to solve the traffic problem? Can anyone imagine the whirlwind of a blizzard that air traffic control would be like? One single accident, and the cascade effect from that?
Reduce global warming? Do you know how much fuel it would take to lift a car let alone go any significant distance with it? Elon's magic flying automobile can do its little tricks for a few seconds, and that's it. It is not designed or intended to really fly any real distance. A couple of $1,000 worth of fuel packed into a mini dirigible drag along tank just to fly to the Walmart, sure, okay.
Same with them jetpacks that we were supposed to be flying around just like the Jetsons - they last like what, 15 seconds is it before the fuel runs out and that's the end of that little trip?
It's this decade's gimmick toy. Every decade or two going back a century there's a yet another new flying car prototype which quite literally goes nowhere and we never hear from again.