A pilot who uses his autopilot or other auxiliary systems remains permanently in a working condition, in his seat with the same body alignment. And if something goes wrong, he usually, not always, has time for corrections.
I suspect that the self-propelled car causes the occupants, especially the driver, to slide into a different mental state. Once a driver has got used to looking away from the road, talking face to face with other occupants, reading, playing with his mobile phone, there is no time at all left before he suddenly grasps a dangerous situation.
That's why the solution can only be completely or not at all automated. There is also another problem. If you really wanted to pay attention to how the car drives, you have to get very tired quickly if you have nothing active to do. It must be a boring and at the same time very strained feeling to drive like that.
