Look at the bridge shoes (lowest visible steel atop the piers) for the main span.
Those four locations support not only the main span, but also half to all (depending on how the cantilever trusses are designed) the weight of both of the next two approach spans, plus any live load (vehicles) those three spans of the bridge are carrying.
That translates to significant (massive) point loads at those locations.
That’s precisely the point I was trying to make. Plus, the uprights/verticals atop the concrete piers not only bear the compressive load that any single internal truss-member would; they bear it for TWO truss sections which share that particular (upright) chord; AND they bear the weight/mass of a bunch of sections. Now, the verticals appear to be composed of 2 channels joined together box-style like so [ ] with intermittent cross pieces, whereas the internal truss members appears to be a straight “I” beam. So they are stronger but not massively stronger.
Add some normal rust, which seems evident from the pix...the unequal load from the one-side-only traffic condition, maybe some fastener deterioration from freeze-thaw back/forth movement.....and you have a news story.
Hey,,,How much SALT is used on that bridge in the winter ??...