I'm in a bus under a freeway overpass as I type this. I pass under here twice a day. The underside is smooth, possibly to keep it easier to clean. I've definite

I'm in a bus under a freeway overpass as I type this. I pass under here twice a day. The underside is smooth, possibly to keep it easier to clean. I've definitely seen overpasses that are not smooth underneath, but certainly not all overpasses and tunnels have space in the ceiling.