I was behind two cars on the freeway, one in lane 1 and one in lane 3. They both decided to merge into the center lane at the same time. I remember the sound distinctly because it was so different than I expected. It sounded like two large, empty cardboard boxes hitting each other. No screeching tires or glass breaking sound (both windshields and side windows broke, but remained intact). It was very unexciting.