We went thru this with my father - he started with Alzheimers and it clearly got to the point that us kids felt he should not be driving any longer. We literally had to take his keys away and then sell his truck in order for him to accept that he just could not drive any longer for his safety and others.

It was a very difficult thing to do but we just had to do it. Now, years later with full blown Alzheimers - he doesn't even know where he is half the time - he will still insist that he could still drive - very scarey.

I wish you luck with reasoning with your father - I know first hand that it can be an uphill battle.