[commish]

Poor writing or explaining -- the 100 tons was not spread out -- the rock was sitting in Dump Trucks all parked in a line (you can see the line of full dump trucks in some of the pictures.)

add to that , that the workers were jackhammering the concrete in the same place, and things start to fall into place (no pun intended).

Weak gusset plates, excessive weight contained in one area, and jackhammers vibrating those plates with all that weight on them.

[crazyshrink]

I didnt hear how the rocks were distrubuted. I didnt see more than one truck on that center section of the bridge that went down first. I assume some had already been dumped in the non traffic lane.

[Mad_Tom_Rackham]

Weak gusset plates, excessive weight contained in one area, and jackhammers vibrating those plates with all that weight on them.

Yep. But mostly, this tragedy is a result of BAD PLANNING. Construction during rush hour, poor load division (traffic and construction materials), vibration effects.