What can you do about a parent that you no longer feels is able to drive, but they don't agree?

I have concerns over my dad driving. When I began a conversation with him, he got very mad at me and is now not talking to me or my brother. We are very concerned about his ability to drive and feel he is a danger on the road. We have started talking with friends of his and his coworkers and they are very concerned as well. He has become very explosive and unpredictable. He is a diabetic and his blood sugar is dipping so low that he is passing out and having frequent episodes. He is under a doctors care and he tells me everything is fine (when he was talking to me). He is very stubborn and is refusing any help or admission that he even needs help. He is in complete denial. I am not sure what to do. He is refusing to even consider moving, although he is no longer able to maintain the house and it has become a health and safety risk. He is refusing to relinquish any driving privileges and won't talk to me about future plans, arrangements or any of his financial situations. I tried to discuss these matters years ago before we got to this point and he refused to talk about it. To my knowledge, he has no will, no health directives, neither my brother or I are on any of his accounts, nor know anything about any of his finances. He and my mother are divorced, so it's just me and my brother to take care of him. We are feeling he is a danger to himself, to others in regard to the driving issues and his explosive nature. We are looking for any guidance possible. I love my dad and want to take care of him, but how do you do that when they refuse your help and become combative?