Slight correction - a properly designed HUD is safer, in aircraft.

Aircraft are not cars - watching for other aircraft is typically handled by air traffic controllers for most aircraft that will have HUDs, or the HUDs are capable of displaying the locations of other aircraft.

Google Glass interfaces are not designed to be HUDs to be used when driving, and there is no ATC or automatic detection of other vehicles when you're in a car.

The two use cases are quite different.

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.

> If you compare a GPS unit the user has to turn their head or worse look down to use vs. a Glass sitting above their vision with the directions always available at a glance, the Glass is pretty clearly superior.

My GPS (actually my phone in a special car dock) is right up on my dash/windscreen, always in my peripheral. I glance at it with ease. And while I am glancing at it, the road ahead of me is in my peripheral. That sounds a lot like what people are describing how to use Glass for GPS. Where are you mounting your GPS that it takes more than a glance to see?

>Heads up displays have already been proven by the military to be much safer.

Correction: Military heads up displays have already been proven by the military to be much safer. In order for their results to apply to Google Glass, they would have to install Angry Birds, Facebook, and YouTube on those devices, too.

The military also have teams of cognitive scientists A/B testing different HUD apps. I remember seeing one paper where they were A/B testing different presentations of incoming enemy fighter craft. This stuff is tested by people who have very deep knowledge about perception and attention, and aren't just an app slapped together in spare time.

I remember from that testing that there were three ways the threat was categorised by distance: safe, lethal, very lethal - the middle one was very specifically not "kinda in danger" :)

> They try to reduce "heads down" time for the pilots looking at their instruments as much as possible.

Do cars integrate with Glass like this?

Cars already exist (off the top of my head I can only think of the Corvette) with HUDs, and they don't have any legal trouble.