At the end of November 1996, Mercedes-Benz presented yet another contribution to the enhancement of road traffic safety. Brake Assist (BAS) shortens the stopping distance in an emergency – when the driver applies the brakes too hesitantly or too gently in a critical situation. In such a case, the system automatically generates the maximum available brake boosting effect in split seconds, thereby shortening the car’s stopping distance significantly. Tests impressively demonstrate the effectiveness of this assistance system: On a dry road, the stopping distance in an emergency braking maneuver from 100 km/h can be up to 73 meters, due to the fact that most drivers step on the brake pedal too gently. With BAS, by contrast, the wheels come to a standstill after just 40 meters – a stopping distance shortened by some 45 percent. Brake Assist formed part of the standard specifications – initially of the S-Class and SL-Class – from December 1996. Today, every Mercedes-Benz car is equipped with Brake Assist.

BAS is an important link in a chain of assistance systems the first of which was the anti-lock braking system (ABS). Based on the ABS, a world first, acceleration skid control (ASR, 1985) was developed to control the interplay of the longitudinal forces between the tires and road surface not only under braking but, for the first time, also under acceleration, by acting upon both the brakes and the engine torque. This was followed by the automatic locking differential (ASD, 1985) and the automatically engaged four-wheel drive (4MATIC, 1985). What all these systems have in common is the recording and limiting of wheel slip by means of advanced micro-electronics and hydraulics with the aim of improving the so-called longitudinal dynamics of a motor vehicle.

The revolutionary Electronic Stability Program ESP® (1995) equally uses the ABS signals. Brake Assist builds upon the scope of ESP® functions. The next evolutionary stage is Brake Assist PLUS (BAS PLUS) which made its debut in the S-Class from the W 221 series in late 2005; this system warns the driver of an imminent head-to-tail crash by means of visual and acoustic signals, and automatically com-putes the brake pressure required to prevent the accident.

Integrating all these components, the PRE-SAFE® brake represents another trailblazing innovation from Mercedes-Benz for optimally decelerating a car in a dangerous situation. It was presented in the CL-Class (C 216 series) in 2006, initially available in this model series as well as in the S-Class. This unique system automatically brakes the car in case a head-to-tail crash is imminent. The PRE-SAFE® brake works together with the Brake Assist BAS PLUS, the latter making its brake boosting effect available as soon as the driver steps on the brake pedal. If the driver does not react to the warning signals emitted by BAS PLUS, the PRE-SAFE® brake initiates automatic partial braking to decelerate the car with some 40 percent of the maximum brake power.

These advanced systems not only use the sensors installed in the car but also state-of-the-art radar technology in order to capture the scene in front of the car and to identify a situation in which an accident is imminent. Mercedes-Benz offers very similar systems for its commercial vehicles, for instance the Active Brake Assist in the Actros heavy-duty truck.