What to actually say
Open with this, more or less word for word: Dad, can I talk to you about the car for a minute, and not about the stop sign.
This isn't about your driving skill, it's about reaction time, and that changes for everyone whether we like it or not.
It separates the fact of aging from an attack on his competence, which is what he's braced to hear.
I'm not here to take anything from you, I'm here because I'd rather have you alive and furious at me than the alternative.
Names the actual stakes plainly instead of hiding behind vague concern language.
What would make this less awful, me driving you, or us setting up a service so you're not asking anyone for a ride.
Moves the conversation from a verdict to a choice, which he can actually engage with.
I know this feels like the first domino, and I don't think you're wrong to be scared of that.
Says out loud the fear underneath the anger, which is usually what he's actually fighting.
How it usually goes
A version of the conversation with the push-back left in, because that is the part you need to have already heard once.
What not to say
You're a danger to everyone on the road.
It puts him on trial, so he defends himself instead of hearing you.
Mom and I already decided.
It turns this into a ruling handed down, which guarantees the fight becomes about control, not safety.
You'll thank us later.
It dismisses what he's feeling right now in favor of a future you haven't earned yet.
If he shuts down and says 'we're done talking about this'
Don't chase him out of the room and don't escalate to win the moment. Let him go, but don't let the subject disappear with him. Say: 'I'm not going to make you decide tonight, but I'm not going to pretend I didn't bring it up either.' Then actually bring it up again later, calmer, maybe with a doctor or the DMV renewal as the reason rather than you. A man who feels ambushed digs in; a man who's had a week to sit with it sometimes surprises you. Some fathers never come around at all, and you have to decide what you'll do then, not just hope.