I got my ticket in San Francisco while I was heading back from the East Bay in the far right lane. I was almost off the bridge when a large 16 wheeler signals to switch lanes into mine. At this point, I was in the middle of the truck and initially got worried, so I let out a signaling honk of my horn in hopes he'd hear me. However, he did not, and was slowly switching into my lane. As a safety reaction, I honked and I gunned it and went past the truck before a serious accident occurred. The truck stayed in its original lane and I was safe. I then returned to a safe speed. Just as I finished, a cop pulled me over for speeding. He wrote me down for 71 when the speed sign was 50. I would say my conduct was necessary to avoid harm and was wondering if I could get any advice/feedback on contesting this ticket. Any help would be appreciated.