The National Transportation Safety Board's leader attempted Tuesday to dispel concerns that the panel's stance against a public hearing on the Interstate 35W bridge collapse was due to a power struggle with Minnesota highway officials. NTSB Chairman Mark Rosenker said in a letter to the acting head of Minnesota's Department of Transportation that the concerns stem from a "misunderstanding" of internal board documents released late last month.
Those documents showed that staffers expressed concern about "losing control" of the investigation and discussed the politics of the issue. The board voted 3-to-2 against a public hearing about the Aug. 1 collapse, which killed 13 people and injured 145.
In his letter dated Tuesday, Rosenker said the Minnesota department has cooperated with the NTSB from the early stages of the probe.
"First and foremost, let me state clearly that the ongoing investigation of the Interstate 35W bridge collapse is proceeding expeditiously with the full and complete cooperation of all the parties," Rosenker wrote. "The Minnesota Department of Transportation has been highly cooperative and collegial, and our joint investigative work has been fruitful."
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Bob McFarlin, the acting Minnesota transportation commissioner, asked Rosenker on Monday to clarify the working relationship of the agencies. A Jan. 17 memo from NTSB staff, he said, "has raised concern among several Minnesota elected officials as to the nature of the NTSB-MnDOT relationship."
The memo had directors of the Office of Highway Safety and the Office of Research and Engineering to the board arguing against a public hearing. They expressed concern that staff preparation for a hearing would delay the investigation.
"It has already taken significant negotiations to keep MnDOT and its WJE technical consultants within our investigation," referring to the Minnesota agency and Wiss, Janney, Elstner Associates Inc.
Any potential delay, such as holding a public hearing, risks MnDOT and the Federal Highway Administration "completing their modeling efforts without our control or input." That could leave the board in an "also-ran position," the memo says.
In his Tuesday letter, Rosenker said a public hearing could take two to four months to arrange and conduct. While such hearings are open to the public, he noted, public participation isn't allowed.
"The document simply expressed staff concerns that those parties might proceed independently if they perceived we were not actively pursuing the investigation for an extended period of time because of the demands of a public hearing," he wrote.
The NTSB has issued preliminary findings that point to a design flaw with beam-connecting gusset plates and heavy loads of construction equipment and material on vulnerable parts of the bridge.