sure, but are you implying that taking your eyes off the road to look down is safer than having directions superimposed on the road, because you're driving and not flying?
Honestly, yes. You have to consciously decide to look down at an in-car UI, and change your focus to match. If something is constantly in your field of vision, it's going to consume more of your attention when you should be watching traffic around you.
My flight instructor phrased it this way. In a car in good conditions, you spend 95% of your time watching your surroundings. In an aircraft in visual conditions, you spend 70% of your time looking outside the cockpit. In an aircraft in instrument conditions, you spend maybe 5% of your time looking outside.
The pilot is focused on the hud first, the outside environment second. A car should be completely reversed from that.
