Fighter pilots go through countless hours of training to learn how to deal with a HUD during air combat. During the other 90% of flight time there's nothing for them to hit if they're not paying attention to the sky. Drivers, on the other hand, go through a few hours of just barley paying attention in drivers ed., and/or a few minutes skimming the book just to pass the test before taking to the road. Automobile driving requires constant attention to the road, and with no training what so ever what do you think joe sixpack will be paying attention to because "I thought I was supposed to focus on the HUD, and it would tell me what to do"?
Remember, 50% of the population is below average intelligence, and I'm sure a good 25 to 30 percent of the above average think they can handle texting while driving as well. HUDs for automobiles is a very bad idea, and there's no reason for them.