When driving in the city, the AR windshield is minimalist and just shows your speed and other essential dashboard information. But whenever you stop at traffic light, the AR windshield fills up with a bunch of notifications and information you're interested in. Or maybe it just opens up the previous app you had open, letting you continue a train of thought.
Discussion
Because you're not driving alone, the passenger seat has their own AR interface, and because you share the same windshield, this could be a social thing. Maybe you're playing a chess game with them, and whenever the car detects that you're driving in safe conditions (or the car is stopped), it's your turn to play.