Imagine that while you're driving, a big line of text that you can't see through appears on your windshield.

Worse yet the text is opaque but you have to concentrate on it to read it.

All this would do is give drivers a false sense of security in your directions example. You'll be concentrating on the text regardless, meaning your concentration is off the road.

Even that autopilot sense where you drive your daily routine for 30 minutes and don't remember minutes 20 of it still has your subconscious aware of obstacles in the road, etc. This would require your concentration to be on the text. Whether you want it to or not.