A safety system for a vehicle includes an imaging sensor and an image processor. The image sensor has an exterior rearward field of view. The imaging sensor captures image data and the image processor is operable to process captured image data to detect an object approaching the subject vehicle from rearward of the subject vehicle. The safety system is operable to determine if the detected object is likely to collide (or that a collision is probable or imminent or unavoidable or substantially unavoidable) with the subject vehicle and is operable to adjust a safety feature of the vehicle before the collision occurs. The safety system may be operable to adjust or vibrate or reposition a headrest of a seat in the subject vehicle responsive to determination that the detected object is likely to collide with the subject vehicle.