There are others who know a lot more than I, except that I have heard repeatedly today that the section over water went first, the middle, not an end, as was reported yesterday.
Reporters agree with witnesses I’ve seen that say they saw the center fail first.
The video shows that the failure occured at the S end of the bridge. That whole section acts like a sheet and fell like a sheet. It fell, because what held the sheet in place on the S side failed across an expansion joint. From the evidence of the torque on the fallen section in Jeffers still above, it looks like a SE side of the sheet (roadbed+trusses) came loose, and that was immediately followed by the SW side popping loose. If you look at the video, you’ll see the roadbed + trusses fall with the S side leading.