PRE-SAFE® Brake uses the same close-range and long-range radar sensors of the DISTRONIC PLUS adaptive cruise control system, which automatically maintains a pre-selected distance between you and the vehicle you’re following.
It’s a three-stage process. If the system determines you will hit the vehicle in front of you, it will set off audible and visual warnings at 2.6 seconds before the expected impact. If the system senses the driver is not reacting, it will engage partial braking at 1.6 seconds before expected impact. If the driver still doesn’t react, full braking will be engaged 0.6 seconds before the expected impact.
This will not avoid the collision; only mitigate its force. The PRE-SAFE® Brake therefore acts as something like an “electronic crumple zone.”
Chris Goczan, Manager of Product Planning, Mercedes-Benz Canada, cited research that revealed that initiating full braking any sooner than 0.6 seconds causes drivers to “jerk the steering wheel or do something else that would make the collision even worse.”
Mercedes-Benz offers all three systems (DISTRONIC PLUS, PRE-SAFE Brake, Brake Assist PLUS) in combination as part of the Driving Assistance package.
(Brake Assist Plus is a system that senses when your braking action is inadequate for an expected collision, and automatically increases brake pressure.)