I suspect there is something to be said
given the requirement for an alert driver, for a control system which steps in if and only if the driver is driving like an utter dickhead...
I'm not at all sure how this might be phased in; it seems that you need either full control or pretty much none. A cruise control saves my ankle, but I still need to steer and brake, and as a result to be alert and aware of what's going on around me. When it does, say, steering and lane control and emergency action and even something as simple as adaptive cruise control, what is left to keep me alert? Electric shocks through the seat?
For a long distance journey where you don't want to drive, take a train or a plane, or even an airship. For the two minute jaunt to the shops, why would you even *want* this sort of automation?