You don't want two windows. Check out the smartglass on the new 787 plane. Electronically dimming glass with variable tint!
Smart glass has been around for a while. It's even available in tint-film form (smart film). I don't know if we can get it in our cars, maybe we're paying our law makers to protect us from it or maybe it has to be flat to work.. just guessing. Either way, it seems like just a matter of time.
https://www.youtube.com/watch?v=cf3WJM72sYs