WARNING: Not surprisingly, some language in this video.

Luckily no one was hurt from this encounter, as the truck driver was able to leave his vehicle long before the train arrived. Fun fact: Those are Nutrigrain bars going all over the place.

According to staff at Willis Tower, the cracked portion you see here was a part of the safety seal of the observation platform and not the glass itself. Still, that's the last thing you want to see when you're suspended that high in the air.