I was driving on the highway utilizing the full self-driving mode. There was traffic and I was behind an 18-wheeler. The 18-wheeler turned into the right lane, but because of the traffic, it couldn't completely clear the lane so the rear was slightly sticking. The Tesla stopped because it couldn't clear the lane while the 18-wheeler was sticking out. I didn't intervene because it had stopped. Then all of a sudden, it surged forward causing the Tesla's right side mirror to be hit by the 18-wheeler's back. The right side mirror's paint job was completely taken off. I didn't have time to intervene because of the sudden surge.