...chain up? I was behind a semi that had spun out half way up a hill on the highway tonight, me and another vehicle. I noticed him unhooking the trailer, was thinking I should get out of there, as I was thinking, the trailer began to slide backward towards us. It stopped just inches from the car in front of me, I had started backing up already, the person in front of me hadn't noticed it sliding. Good thing it stopped! I kinda lost it on the trucker, he told me you need to unhook to chain up. Seems stupid to me?? I would think you could back on top of your chains without unhooking??