Most automatic systems brake proportionally to danger. On their own (without driver assistance) the goal is usually to bring an accident down to a "safe" speed

Most automatic systems brake proportionally to danger. On their own (without driver assistance) the goal is usually to bring an accident down to a "safe" speed like 30mph rather than prevent the crash completely. I guess the point is to strike a balance between trust in the automatic systems and trust in the driver to make the right decisions. Another way to look at it is that the system is designed to protect you, not the car. Use automatic braking to bring the crash down to something the car can protect you from, the rest is up to you