Bridge blame is made official

The National Transportation Safety Board made official what has been clear for months -- that the failure of undersized steel gusset plates was the probable reason Interstate 35W bridge buckled and fell into the Mississippi River last year, killing 13 people.

The board found that engineers who designed the bridge in the 1960s either failed to calculate or improperly calculated the thickness needed for the plates that were to hold the bridge together. The board also blamed state and federal highway officials for not catching the design flaw when bridge construction was approved.

On Aug. 1, 2007, under stress from 287 tons of construction material and rush-hour traffic, the bridge’s center span shuddered, then collapsed, dragging other spans into the river.