I found that adaptive cruise control is something I have to watch all the time, so mostly it replaces one fatigue type by another.
Lane keep assist is quite opposite for me, as it really makes for the substantially less strain from the “fine steering” I need to do (ok, call it “it allows you to be more sloppy”), but still requires to provide inputs of the general travel direction.
How does lane assist work on roads with no lines or on gravel roars?
surprisingly, on the local roads with missing right lane marker it still detects the edge… mostly…
on the gravel roads… you are quite right… it roars 
I was curious as the road I live on the wife describes it as one step up from gravel it is just barley two lane that you have to be right on the edge to pass someone going the other way with no markings at all.
I imagine lane keeping on a road with fresh snow would be like a chameleon on a mirror.
I can only talk to how Honda I own behaves.
If it’s “unsure” - it will simply beep and turn the lane assist off, so more likely than not it would not work on the road you describe
Also black ice.
Thank you I was just curious I have no desire to have one.
I bought one not for this feature too
still, it’s a nice addition you get with the newer generation.
so far, it made a couple of emergency brake incidents on me: it was a guy pulling in front with minimal distance left once and another time the car if front slammed on brakes.
in both cases I was in control, yet I felt it was within the reasonable boundaries to engage as if I did not react simultaneously with the security system, it would not be pretty
I just thought of something else I bet it would go crazy driving across the lines in an empty parking lot. 
hmmm, what would it do with this.
As several have stated, there is no fully self-driving car available, and if there were, you would still have to pay attention to correct any errors.
I have found the Tesla Model 3 (which depending on your state’s rebates and credits might fall in your range) to have an extremely accurate and steady lane keeping and distance dependent cruise control. The car stays in the lane without deviation on curved roads and it works on some roads without markers; it tells you it is turning off when it can’t function right. It does require a hand or two on the wheel generating a small amount of force, not just resting, or it will disengage if your hands are off too long. The lane keeping on this is much better than my Subaru Ascent (a good car) and it is far better than most cars I am behind on a highway! The wandering I see is amazing.
If you are fatigued and think this type of system will make you safer, I am afraid it will not.
My son a truck driver had a truck with adaptive cruise control. When the shadows from an overpass was just right, the truck sensed it as an object and braked hard. Frustrated the devil out of him.
When fully autonomous vehicles are on the road you will NOT have to pay attention. In fact there may not even be manual controls.
The roads with the screwy lines might confuse it. But even the current systems don’t strictly rely on lines. It uses GPS and other road markers. As I’ve stated many many times. The software is still be written. Thousands of lines of code every month is added or changed. Lets wait 10 years before we make judgements on it’s viability. Currently they are at phase 3. Phase 5 is considered road worthy.
Out of those I’d get the Mustang. Just make sure you understand that no car is able to drive itself yet
That’s ticks me off the Subaru EyeSight, which is purely vision-based system.
Having the secondary radar sensor at least gives a second opinion to the computer.
I’ll relate my experience on my car, which has “lane assist.” First of all, unless you’re driving on a 100% level driving surface (front to back and side to side) and your alignment is 100% perfect, you can expect a certain, if minute, amount of drift. On my car, with hands off, it corrects to one side, then the other, in increasingly severe arcs, until the dash gives me a message to put my cotton pickin’ hands on the steering wheel.
Also, on my car (and I expect most others) this feature is controlled by sensors that detect lane markings and the strip usually painted at the edge of the shoulder. You should note there are plenty of places, mostly rural, that lack that painted edge. That being the case, this feature will not function at all and if you’re not paying attention you’ll go off-roading.
Finally, with hands on the wheel, if you drift too far toward the edge of your lane, you get a slight tug on the wheel to turn the car back to the center of the lane. This can become somewhat stronger if you have to suddenly change lanes; you have to remember you MAY need to use a stronger then usual amount of force to make the car change lanes.
Bottom line: I’m indifferent myself about having this feature, but there is absolutely no replacement for keeping your hands on the wheel and paying attention to what’s going on around you. Emergencies are just that - they happen without warning and you need to always be ready to respond.
… or recall your car has blinkers ? 
the moment you signal the lane change, lane keep assist will turn off
