Eyes being on the road doesn't mean your mind is on the road. Looking for problems is an active process, and if your brain isn't engaged it won't matter where you're looking.

Playing with adaptive cruise's following distance can keep a driver engaged with driving situations while retaining the benefits of adaptive cruise. Not sure if there is an analogy for lanekeeping.

That is a problem even without this kind of technology.

This is a good point, although I do think there is an argument for a greater tendency to "mentally wander" if you aren't physically engaged somehow.

If you are long distance driving on straight empty highways, it is easy to get into the wandering state. I find these features only useful in those cases where engagement is difficult to maintain anyways.

Very true, and that situation is the only time the feature appears to work. Minimal repetitious physical engagement wouldn't change much I'm guessing.

Ya, I never use them for city driving. It is just that once a year cross country western trip where it comes in really handy.

I seriously question this kind of system. The Cadillac system seems to work by using IR light and cameras to make sure your eyes are open.

I worked with a system like this many years ago in a transportation research firm. The way it worked was that it used bright IR LEDs at two different wavelengths, pointed at the driver's face, and then cameras tuned to both wavelengths, and then subtracting the images to see if the driver's eyes were open.

I sat in front of this system some, but not for any long drives, and even then I felt very uncomfortable after 10 seconds or so. While humans can't directly see IR light, I definitely felt something there, probably from the very near-IR LEDs.