In my experience doctors don't get into this with patients. I got our doc to write my mother a letter which she ignored. What worked was a driving evaluation- cognitive and on the road- which she failed miserably and they took her license on the spot.

I got her there by telling her that if she was sick and tired of people telling her not to drive, she should go to the evaluation to prove she was able to. It felt manipulative but she never got angry at me, only at the rehab folks. She talked about hiring a lawyer for a couple of weeks and then forgot about driving.