My Brother's Threatening Behavior

Anger is tough. I was the angry child. I feel as if you go straight to your parents without acknowledging him first he will probably just get angry and stubborn. I would've done the same. Approach him when he's calm and bring up carefully the fact that you're worried for him (as well as your) safety when he gets angry and suggest he might benefit from professional care. If that doesn't go well you can try parental involvement but fair warning an angry person will probably just get angrier if that's the move. Very difficult situation. I do hope he finds ways to manage it.

Agreeing with what SoxyWoxy. Threatening to drive the two of you into a ditch because of his anger is not healthy and is indicative of mental illness. Don't go to him about it. Go straight to your parents. This is not a situation that you can just talk out with him. Make sure to emphasize the need for professional help to your parents. It may make things worse if they just try to punish him instead of getting him help. Talk about being worried for his well-being as well as being afraid for your safety.