At Mercedes-Benz they have gone a step further. They have combined primary safety, which has the purpose of preventing an accident, with secondary safety, which provides protection during a collision. At speeds above 30 km/h, PRE-SAFE monitors the dynamic state of the vehicle (speed, sway, etc.) and the actions of the driver who operates the steering wheel, the accelerator, and the brake pedal, in order to determine whether or not preventive action is being undertaken. If it is, then the system deems that a collision is inevitable, and among other measures tightens the seat belts using the reversible seat belt tensioners; optimizes the seating position of the occupants if the seats can be electronically adjusted; and, if the car sways badly or if there is lateral slip and a side collision or a rollover accident is expected, closes the automatic windows and sunroof. All the PRE-SAFE® actions are reversible: if the collision is prevented, the tension in the seat belts is released and the occupants can adjust their seats again.