My understanding is that in this case Mercedes if fully liable if something goes wrong - so you are allowed to watch a movie or read a book. If the car proceeds

My understanding is that in this case Mercedes if fully liable if something goes wrong - so you are allowed to watch a movie or read a book. If the car proceeds to crash into the car in front of you, Mercedes is on the hook, not you. I doubt your liability is waved when reading a book while using the adaptive cruise control in your car.