[PeppyGPhiB]

Driver B is at fault. I had the exact same thing happen to me several years ago, and I was Driver B. It was at night time and it was snowing, and the driver behind me didn't have her lights on. Even though I was looking behind me in my mirrors, I couldn't see her. I thought she was driving negligently, and I had witnesses that even said they couldn't see her, but that didn't matter...I was still at fault because the person backing up is almost always at fault in an accident.