The design and installation of a number of components of the Nipigon River bridge were responsible for the structure's failure, according to results of an investigation released by Queen's Park on Thursday.

In January, the bridge unexpectedly heaved apart, closing the Trans-Canada highway about 100 kilometres northeast of Thunder Bay, Ont.

In a joint statement from Steven Del Duca, Ontario's Minister of Transportation, and Michael Gravelle, the Minister of Northern Development and Mines and MPP for Thunder Bay-Superior North, the province said that "a thorough engineering analysis" found three main factors led to the failure:

  • The design of the shoe plate and its flexibility
  • A lack of rotation in a bearing that was constructed
  • Improperly tightened bolts attaching the girder to the shoe plate

"The safety of the travelling public is of paramount importance to our government, and we appreciate the ongoing patience and understanding of the people who use and depend on this bridge," the statement read, adding that neither cold temperatures nor wind were responsible, and that overloading — not any kind of flaw — caused the bolts to break.

The two ministers visited the bridge site on Thursday.

The province and independent engineering consultants analysed the bridge and the bolts after the January 10 failure, which closed the Trans-Canada highway for 24 hours, severing the link between east and west.

Provincial officials had already received the reports, but announced in July that they wouldn't be made public until the fall.

Retrofit work slated to be done during winter

Initial cost estimates for repair work range from $8-12 million according to the statement.

Work is slated for the winter to implement a permanent retrofit design for the structure. "This permanent retrofit will ensure that the Nipigon River bridge functions safely for road users throughout its intended useful life," the statement said.

In addition, the province said it will undertake a planning study and an environmental assessment in the fall, aimed at creating an emergency detour route. That is expected to take approximately 18 months.

"While our government has full confidence that the retrofit, once complete, will ensure that the bridge is safe for all users, this detour route would provide an alternate option for local residents and businesses in an emergency," the provincial statement read.

Nipigon Mayor Richard Harvey said Thursday he was happy to hear a detour route is in the works.

"We started talking about it over 10 years ago when we were doing emergency exercises, and recognized the need for that" Harvey said. "We're very pleased."

The $106-million Nipigon River Bridge project, the first cable-stayed bridge built in Ontario, opened its first two lanes about two months before the failure.