Pittsburgh allegedly has more bridges than any other city in the world. One collapsed last January.[0] I had driven over and walked under it many times. An uncomfortable number of other bridges in the city are in poor repair.[1] If one of the bigger ones over one of the rivers here collapse, it will be a tragedy of similar magnitude to your nightmare.
[0] https://triblive.com/local/frick-park-bridge-collapses-natur...
[1] https://archive.ph/5u4de