We saw something similar on the way back from St Augustine, FL last fall. A semi driver was carrying an excavator and didn't have the arm all the way down. He hit the crap out of the I-75 overpass on I-10W. A lot of concrete chunks came down on the road and several low riding vehicles like sedans drove over them, damaging the underside of their cars. I was fortunate enough to slow down and avoid hitting any of them.
Shortly after that, I started seeing a lot of signage going up right before reaching an overpass warning about this. Has a pic of a dump truck with its bed UP, warning drivers to make sure their bed is down.