That is dangerous, and reckless, and goes against everything you've ever taught him?
Your level-headed kid who is so smart. Whose friends sometimes do these kinds of things, but he doesn't.
I took his car away. I told him that there is no way he is going away to school in 3 weeks if I cannot trust him. I told him that I needed to keep him safe, and if letting him out of my sight means he puts himself in danger, then he is not allowed out. That I didn't raise a kid to be almost 19 to stand by while he risks his life.
What else do you do?