This is a good answer, and always an important consideration. Here is a little handout we refer to a lot re: "the driving issue": http://www.agingwisely.com/wp-content/handouts2011/TakingAwayKeys.pdf. However, as mentioned in the article, it is important to keep in mind the judgment issues related to dementia, which compromise not only the driving but the decision-making about stopping. We all too often hear families say their loved one has mild dementia, and "only drives locally" or "during the day" or "two or three places within a mile"...which may be true until he/she ends up lost one day or something throws off the routine and complex thinking is compromised too much to manage it.
Some docs are better than others about this. As care managers, we often have to be the person's advocate as you are for your loved one--we've had a family doc of 30 years for one client...just too close to the situation so unwilling to do anything. There are independent driving assessment programs in many communities--one way to take the emotion out of it and let an indep. test tell. Some of our local memory clinics provide them, so that may be a way to have your Dad "check in" on how he's doing now (and then perhaps every so often if he's ok now).
Also, don't forget if he does give up driving...he still needs to stay active and vital...make sure he has ways to get around--friends, family, local transport services, home care company, cab, etc. We call it "Drive to Thrive":-) http://www.easylivingfl.com/wp-content/uploads/2011/01/Drive-to-Thrive-for-website.pdf since driving is vital to getting out and about in most areas in the U.S.