About the same as moms in my experience. Mine won’t stop driving, though she absolutely should. I just have to hope she doesn’t kill someone.
The difference between you and me is that mom can afford to buy her own new car whenever she wants, so I can’t act as a gatekeeper as long as she is mentally capable of making her own (bad) decisions. You’re in a better spot; if your dad is an unsafe driver, you can choose not to enable his driving by not providing him with a car.
I agree with the many others. Get him set up with Uber/Lyft and keep him, and everyone around him, safe.