Loving the game, it's fun as an optimization puzzle and as a generator of lovely little scenarios...
Having a slight issue with adding people to nearly-full cars, though? Sometimes it seems like I'm unable to add someone to a car, but if I remove people then re-add those same people in a different order then it works? I'm not sure if it's a bug or just that the clickable areas are really specific, though? Maybe having a "this click will succeed"-type hover outline or something as you mouse around would help.