Now, not to steal KitaYama's thunder, but I've been hit by road debris, similar but not identical to the case of that bus driver . In my case, I was in the front passenger seat, part of a car pool group. We were heading for work on I-10, in the left-most lane - for our non-USA friend, the "fast lane" because we drive on the right side of roads. In the center lane (of a 3-lane highway), a speeding panel truck drove past us, moving faster than us, and rolled over a section of a truck's leaf spring that must have broken off earlier. Basic road debris. I'm going to guess it was 7 or 8 inches across and approximately square - but slightly curved, not flat. Maybe 1/2 to 3/4 inches thick.
Apparently the panel truck rolled over it in a way to flip it up into the air. I didn't see it coming, but that bit of metal sliced through the windshield on my side, and hit my briefcase, which (fortunately for me) was reinforced steel-frame construction, lying in my lap. The metal segment bounced off the briefcase, which was slightly dented but still structurally intact. I still have it as a reminder.
The bouncing debris hit my hand, and then bounced up and caught me in the jaw. Most of its force was absorbed by the impact on the briefcase, and the hand strike was glancing - but the jaw hit was square. No broken bones or teeth, but - as we say sometimes about boxers - it rang my bell. The driver took the fourth hit but only as a glancing strike, and she was not knocked out. She was able to bring the car to a safe stop on the right-hand shoulder of the road. The third member of the car pool was not injured because the debris ended up in the floor beside her in the back seat. None of us had cell phones at the time because this was in the late 1970s and cell phones were clunky things that wouldn't fit in a pocket. Therefore, we couldn't call for help. The third person directed the driver to a nearby hospital with an emergency room, which she knew about because she had been there herself in the past.
I remember the post-impact drive in flashes of momentary consciousness alternating with a few blurry "don't give a damn" moments, but by the time we got to the hospital, I was a bit more coherent. Still dizzy, but eventually able to walk on my own without losing my balance. No stitches, and the X-rays said nothing broken. The next day I visited my dentist to verify no tooth damage, and I was lucky, I guess. Didn't even dislodge any fillings. The aftermath was that for a few days, my cheek and jaw were swollen like one side of me had become part chipmunk, and I had a little bit of a black eye.
From personal experience, I can tell you that a road debris hit is no joke. I also have a great deal of reluctance to throw away that old briefcase for some reason, perhaps because of what it shielded during the incident.