Here in Massachusetts, there are many concrete highway overpasses dating from the 1920s. For years, I was nervous about driving under them. People thought I was crazy. About five years ago the highway department began putting nets under them. Some chunks must have fallen out.
You don't want to hit any size of concrete chunk while driving at 55 mph.
I'm amazed that they are still building new overpasses with concrete, like the giant ones on Rte. 84 near Hartford, CT.