The board has a meeting scheduled for Thursday, where it plans to release a draft report identifying the cause of the Interstate 35W collapse, which killed 13 people and injured 145.
In January, NTSB Chairman Mark Rosenker said a design error was "the critical factor" in the collapse. He cited too-thin gusset plates, which helped connect the bridge's steel beams.
Rep. Jim Oberstar, a Minnesota Democrat who chairs the House Transportation Committee, has criticized the board for coming to conclusions before the investigation is complete.