I once saw an entire wheel break off of a logging truck on I-5 near Tacoma, bounce up and over the Jersey barrier into oncoming traffic. I was in the oncoming left lane, it hit in front of me, bounced up and over me and wiped out cars behind me. Miraculously nobody was killed, but when I stopped to help, we had to pry the woman behind me out of her car with tire irons. The wheel hit dead center on her hood, then bounced again so it didn't come through her windshield, but it folded her car so bad that none of the doors worked. That was one of my scariest moments on the road.
A few years ago my wife and I were delivering a car to her sister in Minneapolis and when driving through Nebraska, I watched as an unsecured kayak on top of a car just lifted off and went airborne. It flew right at my wife's car windshield next to me but at the last second, caught a wind gust and sailed over her, then went through the windshield of the car behind her. Again, nobody killed or seriously injured, but we went out and bought lottery tickets right after that.