Transport Quebec will release a list of some 135 highways flagged for extraordinary inspections because of suspected structural problems.

The province's transport ministry is also lowering maximum weight allowances for large transport trucks on affected highways because of concerns the roadway may not be sound enough to bear the weight.

Transport officials said they will release the complete list Thursday afternoon at a press conference in Montreal.

Inspectors are currently taking core samples to determine road stability, something that could take at least to the end of the summer.

The transportation department has come under fire for keeping its list of targeted bridge and overpass structures secret despite repeated demands from the province's trucking industry to publish it.

The Quebec Trucking Association pressured Transport Quebec to release the list, saying weight restrictions will likely drive up transportation costs and that could trickle down to the consumer.

But it's important everyone know which structures are under scrutiny, said president Marc Cadieux.

"We need that list of structures if we want to reorganize our roads, and want to reorganize our delivery," he said on Wednesday. "We have to be in knowledge of those restrictions."

Transport Quebec has already shut down two lanes on the Félix-Leclerc Highway in the provincial capital area after a special inspection this week revealed structural defects in two overpasses spanning the road.

The lanes are closed until at least Friday and heavy trucks are restricted until engineers complete further testing, evaluate core samples and effect necessary repairs on two overpasses bridging Labelle Street in the Beauport borough, east of Quebec City.

The closures are a precaution and people shouldn't get alarmed, officials said.

"If there was the slightest chance they would fall, the overpasses would be closed," said Jacques Gagnon, a regional director with Transport Quebec, in an interview with the Montreal Gazette.

Transport Quebec has banned trucks weighing more than three tonnes from the Félix-Leclerc Highway in Beauport. Two lanes will also remained closed to traffic until necessary repairs are completed. Alternate routes include Henri-Bourassa Boulevard and the Dufferin-Montmorency Highway.

The closures come as Quebec's Transportation Department has had to defend its bridge inspection procedures, after being severely criticized at the Johnson Commission investigating the Laval overpass collapse.

The commission has been asked to establish causes that led to the Concorde overpass collapse that killed five people and crushed several cars on Sept. 30, 2006, north of Montreal.

Expert testimony from various engineers suggests a "perfect storm" of factors, including poor design and construction and inadequate inspection rules that allowed fissures to grow on the Concorde overpass, weakening the structure to the point it could no longer bear the weight of regular traffic.

Several experts have testified the fissures should have been noticed during routine inspections, which they argue are not rigorous enough.

This week experts summoned by Transport Quebec's lawyers dismissed those accusations, testifying there is no way inspectors could have noticed fissures in the Highway 19 overpass.

The head of the commission, Pierre Marc Johnson, has on separate occasions expressed concerns about the safety of similar bridge structures in other parts of the province.

His warnings prompted the Transport Ministry to promise further inspections of 135 road and bridge structures across the province.

Last week engineers destroyed an overpass on Highway 20 in Sainte-Hélène-de-Bagot, in the province's Montérégie area.

About eight of the highway structures scheduled for inspection are in Montreal.