The radar-based brake assist system.

Mercedes-Benz Intelligent Drive


BAS PLUS monitors vehicles ahead and optimises the applied brake power as soon as the driver steps on the brakes – initiating emergency braking, if necessary.

The BAS PLUS brake assist system forms part of the optionally available DISTRONIC PLUS package and can help to avoid rear-end collisions or at least to reduce the speed of impact.



BAS PLUS employs the same watchful "eyes" as DISTRONIC PLUS: two radar systems which carry out long-, mid- and close-range monitoring of the area in front of the vehicle. These systems are particularly good at detecting moving objects ahead, calculating their distance in front and determining the relative speed between vehicles in front and one's own car. When the assistance system recognises an impending rear-end collision on the basis of this information, Brake Assist PLUS goes into action. The electronics then calculate the necessary deceleration automatically. When the driver subsequently steps firmly on the brake pedal, BAS PLUS recognises the driver's braking intention and optimises the brake pressure automatically. BAS PLUS enables controlled precision braking according to the given speed and distance and increases the brake power as necessary – applying full emergency braking in the most extreme cases. BAS PLUS intervenes only when the driver's braking response is not sufficient. When the driver takes his foot off the brake or the radar shows that the way ahead is now clear, BAS PLUS ends its assistance function.

More detailed information


Changes may have been made since these images and films were produced.

Sensors which scan the area ahead of the vehicle and recognise dangers in a fraction of a second form the core of the BAS PLUS assistance system which is available in conjunction with the optional DISTRONIC PLUS package.



Brake Assist PLUS uses the information from two radar systems. A long-range radar system under the radiator grille scans the area in front of the vehicle with a beam angle of 18° over a range of up to 200 m (as of model year 2009, previously 150 m), covering up to three traffic lanes. Model year 2009 also saw the introduction of an additional mid-range scanning zone for this new sensor, covering a distance of around 60 m at a beam angle of 60°. Two particularly wide-angle short-range radar sensors are additionally concealed behind the front bumper with an 80° field of vision and a range of 30 m.


As with the airbag, the belt tensioner, ESP® and other trailblazing safety systems, the hard facts on accidents again provided the starting point for the development of Brake Assist PLUS – more precisely, the high number of serious rear-end collisions. The DISTRONIC PLUS and BAS PLUS assistance systems from Mercedes-Benz employ state-of-the-art radar technology to warn drivers when they are too close to vehicles in front, also providing support in emergency braking. In this way, the systems make an effective contribution towards reducing the incidence of such collisions. This is confirmed by an analysis conducted by Mercedes-Benz on the basis of representative accident research data. In Germany alone, this technology could prevent one fifth of all rear-end collisions. On motorways, the number of accidents could be reduced by as much as around 36 percent.



The developers have considered drivers following the braking vehicle, too. Adaptive brake lights which flash rapidly when emergency braking takes place with BAS PLUS warn vehicles behind and can help to reduce their stopping distances.


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