Tudor Van Hampton The contractor that began repairs in June had prior experience with the I-35W span, said NTSB Chairman Mark Rosenker (center).

The contractor hired to resurface and repair the road deck of the Interstate 35W bridge that collapsed on Aug. 1 had prior experience working on it, according to officials with the the National Transportation Safety Board.

The construction firm, which began work on the bridge in early June, is a "an experienced bridge and deck repair contractor," says Mark V. Rosenker, chairman of NTSB.

Federal investigators have interviewed employees of the firm, Progressive Contractors Inc., St. Michael, Minn., and have received preliminary documentation, such as field diagrams, of jobsite activities.

Construction "is an additional area that we need to be examining," says Mark V. Rosenker, NTSB chairman. "But it is no more of an interest to us than any other aspect of the investigation."

NTSB is looking at equipment, materials, craft staging and the flow of work for the $9-million overlay project. It will then take the data and plug it into a finite–element analysis program of the bridge.

"We need to have an accurate depiction of what the bridge was like at the time of the accident," says Rosenker.

The software program, which NTSB obtained from the Federal Highway Administration, had to be reconstructed. The original software, which was used in a 2001 University of Minnesota study of the bridge, was not available.

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By plugging up–to–date details into the new version of the model, "we are going to have, we believe, an even better program," says Rosenker.

"We are pleased to have some tools that we didn't have in the Big Dig," he added, speaking of last year's fatal concrete plenum collapse inside the Central Artery/Tunnel in Boston.

The I–35W bridge's de–icing system, installed in 1999, will also be plugged into the analysis software. No other electronic monitoring equipment was found on the bridge after the collapse.

PCI had the bulk of its crew and equipment on the southern end of the I–35W main span, according to NTSB's initial review. Crews had blocked off two northbound side lanes of the structure's four lanes.

The federal probe turned its attention away from the southern end of the bridge after preliminary investigation found no evidence of failure there.

"Everyday, we make more progress in finding out at least where the failures are not," says Rosenker.

The federal probe could take up to 18 months, notes Rosenker. "This is going to be a very long and thorough process."

Meanwhile, the Minneapolis Police Dept. has officially identified Greg Jolstad, 45, as missing. Jolstad was operating a skid–steer loader at the time of the collapse, according to eyewitnesses. His body is still likely to be buried in the debris field, local authorities say.

Police dive teams say they have not yet identified any heavy equipment in the wreckage.