Rotating a bridge into position - GIF

[Frank S]

I believe this is for construction purposes not utility.

That would be one possibility. We see a lot of bridges constructed in the north east states where they build the bridge then over night install it on the footers

Another possibility would be if the road was an interconnecting highway to another country and you wanted to restrict an invading force having easy access just rotate the bridge Or wait until they were on the bridge then rotate it. Shooting fish in a barrel comes to mind