The accident avoidance system engaged during a 55mph drive on a divided 4 lane road. no other cars on road, no animals. Car swerved sharply to left half way into left lane and brakes engaged sharply, enough that driver and passenger in front went forward. after clearing warning, and proceeding down the road a few hundred feet, same thing happened. Has also occurred during navigation of a sharp curve, possible due to picking up a small reflection sign well off road.