In the event of an impending rear-end collision, PRE-SAFE® Brake prompts the driver to take action by means of visual and acoustic signals.

The anticipatory brake.



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When an impending rear-end collision is identified, the innovative PRE-SAFE® Brake system prompts the driver to take action by means of visual and acoustic signals. If the driver fails to take action, the PRE-SAFE® Brake additionally triggers a vibration signal to warn the driver and is able to carry out autonomous partial braking to reduce the vehicle's speed.

If the driver still fails to react, the PRE-SAFE® Brake is able to initiate emergency braking shortly before the now unavoidable collision, thereby substantially reducing the severity of impact. PRE-SAFE® Brake and BAS PLUS Brake Assist work together here. These two assistance systems form part of the DISTRONIC PLUS adaptive cruise control package. This is how the innovative systems work in the fractions of a second before the identified and calculated time of a potential rear-end collision: approx. 2.6 seconds before: visual and acoustic warning of potential collision and commensurate additional brake power from BAS PLUS when the driver steps on the brake. Approx. 1.6 seconds before / after three acoustic warning signals: if the driver now steps on the brake, BAS PLUS Brake Assist will provide support as required by the given situation. A rear-end collision can often be prevented in this way. If the driver fails to react, the PRE-SAFE® Brake will automatically initiate partial braking to attain deceleration of up to 0.4 g – corresponding to around 4 m/s² or approx. 40 % of the maximum braking force. The available PRE-SAFE® functions are additionally activated in the interior (see PRE-SAFE® system). Approx. 0.6 seconds before: if the driver still fails to respond, the PRE-SAFE® Brake can initiate autonomous emergency braking to further reduce the severity of impact and the possible consequences of an accident. The system operates in the speed range from 30 to 200 km/h.



Cutting-edge radar technology is able to help identify an impending accident. Two short-range radar sensors located behind the front bumper panels with a scanning angle of 80 degrees monitor the area up to 30 metres in front of the car. Thanks to a special drum technology, the latest generation of the long-range radar behind the radiator grille is able to provide both long- and mid-range coverage: in the long-distance range up to 200 m with a scanning angle of 18 degrees; in the mid-range up to 60 m away from the vehicle with a scanning angle of 60 degrees. While PRE-SAFE® Brake provides the driver with a visual and acoustic warning of an impending rear-end collision, BAS PLUS automatically calculates the necessary brake pressure and supports braking by the driver in response to the warnings as appropriate to the given situation. In extreme cases, this takes the form of emergency braking.


If the driver brakes very heavily from a speed of over 50 km/h or if BAS Brake Assist is activated in emergency braking, the adaptive brake lights warn the traffic behind by flashing at fast intervals. When the vehicle comes to a standstill after such emergency braking, the brake lights revert to continuous mode. In case of emergency braking from a speed of over 70 km/h the hazard warning lights go on automatically when the vehicle comes to a standstill and go off again when the vehicle continues its journey.


Road tests carried out by engineers from the ADAC German Automobile Association with PRE-SAFE® Brake, stage 1 (autonomous partial braking) in 2007 revealed that the "electronic crumple zone" of PRE-SAFE® Brake, stage 1, reduced the impact speed by 12.5 km/h, resulting in collisions in the conducted tests at a speed of only 37.5 km/h instead of 50 km/h, for example. This corresponds to a reduction of around 30 % in the forces acting on occupants in the front, while forces in the rear are reduced by as much as 45 %.


Current measurements by Mercedes-Benz engineers show that a reduction in speed by as much as 30 km/h is attainable by a combination of partial braking followed by emergency braking (PRE-SAFE® Brake, stage 1 and 2).


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