Necessary

I would put the sign about 6 inches higher than the bridge. That way, it'd still be a true statement, "if you hit the sign you hit the bridge", but there'd be that one guy who's shorter than the sign but taller than the bridge. And for him it'd be worth it.

Why do I get an urge to check if that's actually true?..

there's a lot of video of trucks hitting that bridge before the sign was put up

Thanks for placing the sign after all the exits...