It sounds to me like some kind of lock-down area that bad guys can't shoot their way into.
Personally, I'm surprised they don't just avoid the area entirely rather than go to the trouble of (what amounts to) rebuilding the bridge superstructure...
From RFC 1925: "(3) With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead."