This happened to me on Saturday: I was in the left lane of Interstate 40 west bound through New Mexico with Autopilot engaged (TACC + Autosteer), passing an 18-wheeler in the right lane. The 18-wheeler driver apparently got distracted, and began drifting out of his lane to the right. You can hear his tires run over the rumble strips on the right. He overcorrected back into his lane and partly into mine. The Tesla sounded the Side Collision Warning alert, and I believe also did a slight Side Collision Avoidance maneuver by nudging the car to the left side of the left lane. I then sped up (you can hear the speed limit warning chime) to avoid being next to him. I cannot say for sure whether the car nudged the vehicle to the left or I did. When I looked at the video, I don't think I reacted that fast, leading me to believe that the car did so. It's also possible that both actions occurred, with one or the other first. I wasn't going to contact the trucking company, but someone on the Tesla Motors forum suggested I should. The owner of the company commented on the video and says he will forward the information to their safety department for review. I told him I didn't want the driver to get into trouble, especially since there was no collision. Anyway, I found it very interesting and reassuring that the car's safety systems appear to be this good.