Just make the car turn on the warning lights and gently come to a stop when the driver lets go of the steering wheel or is otherwise not paying attention.
There are two possibilities:
1) The driver is actually incapacitated. Then slowing down and stopping is a million times safer than continuing to drive.
2) The driver was looking at his mobile phone. Then he'll probably quickly react and take control of the car again.
I don't see the scenario where continuing to drive is safe when the car knows the driver isn't paying attention.
Big city highway traffic where the road is crowded and moving fast. Those people aren't paying attention either and will slam into you. I've seen cars stopped on the freeway a few times in Atlanta because they broke down and it causes a big wreck. Responders really rush to get them off the road because it's so dangerous.
There are two possibilities:
1) The driver is actually incapacitated. Then slowing down and stopping is a million times safer than continuing to drive.
2) The driver was looking at his mobile phone. Then he'll probably quickly react and take control of the car again.
I don't see the scenario where continuing to drive is safe when the car knows the driver isn't paying attention.