It was an old bridge (40 years or so) and they've been working on it forever ... I don't doubt the construction work brought it down. No reason to think it was anything more sinister.

Up in this part of the world we have a saying about the 4 seasons: almost winter, winter, still winter, and road construction. Believe me, it holds true in Mpls! I haven't been there in probably the last 5 or 6 years where SOME highway hasn't been in the midst of work!