It's not a solution (you really shouldn't drive when you're sleepy) but a great many modern cars will warn you if you slowly quit your lane without having used

It's not a solution (you really shouldn't drive when you're sleepy) but a great many modern cars will warn you if you slowly quit your lane without having used your blinkers first, which is typically what happens when someone get sleepy while driving (slowly drifting out of your lane on the highway). My wife's little Toyota CH-R does just that: it tries to correct the car's trajectory, does give feedback both through vibration (in the steering wheel) and through an audio signal. I think it's more realistic to settle for that kind of features than to wait for a real 100% complete autopilot.