Most studies so far on Advanced Driver Assistance Systems have assumed perfect knowledge of driving conditions, driver intents which require expensive sensor suite, data communication and processing. In this paper, we study a fairly restrictive driver assistance system supporting "blind spot", "lane departure" detection and "safe following distance" monitoring. A vision-based active safety system is presented to prevent possible traffic accidents during lane change maneuvering and lane following tasks. The active system considers that the driver is always in-the-loop and in case of lane departure detection or lane change unintentionaly into the path of the coming vehicle, visual and audio signal is generated to warn the driver. Design and implementation issues of the developed low cost active safety system are presented.