Maintenance wasn't the problem.
The bridge was built in 1955, and while considered 'safe', and not in dire need of repair, the design was functionally deficient (too narrow, no shoulders, not high enough for modern transport). The state had no plans to replace it (until now).
The truck that hit it was carrying a large steel girder drilling platform. The truck was part of a two truck convoy with a leader truck and a follow truck. These guide trucks are supposed to move into the left adjacent lane when they are approaching a low structure like this bridge and slow down to allow the trucks to drive slowly down the center of the roadway (straddling lanes) in order to cross under the highest point.
In this case, the second truck had engine problems, and pulled off at a rest stop with the follow truck while the leader truck and one of the semi's continued on.
This left no lane protection from the rear, allowing vehicles to pass on the left lane and preventing them from moving under the highest part of the bridge opening.
The load was too wide for one lane, and too tall for the right lane because the trusses were arched and lower towards the outside edges.
The top right corner of the drilling platform hit the right edge of the truss where it met the right side of the bridge, compromising the integrity of the support structure.
The impact was strong enough to tip the loaded 18 wheeler onto it's left side wheels.
The truck was able to continue safely across the bridge before it collapsed.
Here is a news article, and a picture gallery
http://www.seattlepi.com/news/us/articl ... php#page-2Here is a picture of the truck with the drilling platform on it, with the still in tact end of the bridge in the background.
Here is a good visual of the collapsed segment of the bridge (south end). You can see the truck that hit it on the far right side of the image.