Longitudinal control system for a motor vehicle

The invention relates to a longitudinal control system for a motor vehicle having a sensor system for detecting the lying ahead traffic situation, in particular for locating vehicles traveling ahead, and a control unit for automatically controlling the speed or the acceleration of the motor vehicle as a function of the ahead traffic situation to a standstill, wherein an automatic driving off is permitted without an acknowledgment driver within a predetermined time interval from reaching standstill. According to the invention the time interval is variably predetermined thereby, preferably in dependence of the estimated driver's attention and accompanied by a startup warning to the driver.