Driving

My father taught my mother to drive when she was 23 (in 1942). I really can't imagine what kind of teacher he was. When he taught me I was 16. He was pretty patient with me except for the time I hit a garbage can in a gas station.
My mom was direction impaired. Her motto was, "always have a tank of gas". I unfortunately inherited that gene. This is why I have a GPS.
She was also a very careful driver. After her car was rear-ended she became a nervous driver.
Driving is another area when you don't how dangerous driving can be until after the danger has presented itself. The police, the insurance companies and the Department of Motor Vehicles are of absolutely no help in this area.
For most people, their car is their independence; and trying to convince someone to give up their independence is as hard as it was for me to eat boiled to death frozen broccoli when I was a kid. 
As she got older, you could no longer see her head in the driver's seat from the back of the car. For the rest of us drivers, we know that is not a good sign and these cars are to be avoided at all cost. She was no longer able to make left turns. She could not pump her own gas. She got lost on a hospital's grounds for over an hour.
She arrived home at 9PM without her lights on and parked the car on the lawn as if she was drunk (she was not).
It became clear she could no longer drive without it being life threatening, to her and anyone else on the roads or streets.
I was fortunate in that I was living with her by that point. We hid the keys and drove her everywhere she wanted to go. Of course, Tee thought that she could still drive. Oy he is a pain.
I don't know what the right answer is, but allowing someone to drive who is no longer able is definitely a bad idea.