The way it fell down is telling.

The center deck dropped, then the approaches pulled back from the piers and fell. It seems to me that there must have been some members under the road deck that were in tension. Those tensioned members if they ran from one bank to the other and were anchored, would gradually have to take more and more of the load as the other members of the truss fatigued cracked and stopped helping.

When they gave up the fight, what remained just buckled. The piers were only thick enough to hold up the bridge, not resist lateral pulls along the road direction. Indeed you would want some kind of bearing on top of the pier that would let the road bed and truss glide back and forth.

I guess we'll see if that analysis holds up when the experts make their report.

On another note. I'm beginning to suspect that Minnesotan ideas as to what constitutes bumper to bumper traffic is different from that of the SF Bay Area.