---

How could this happen?
That's the question that is surely on the minds of many people in Quebec after five people were killed when a viaduct collapsed this weekend and the province plans to hold an inquiry to answer that question and the many others that have arisen after the tragedy.

The Quebec government announced Sunday it will hold hearings into the accident in which an overpass in Laval, north of Montreal, collapsed, causing huge slabs of concrete and vehicles to rain down on two cars underneath, leaving the victims inside with no chance of survival.

Former premier Pierre-Marc Johnson will head up the review.

The structure collapsed around noon Saturday and the debris landed on Highway 19 - a busy thoroughfare that links Laval to Montreal. Six people were also injured.

"The public inquiry will allow us to understand the situation that is exceptional because no expert can explain to us how a modern structure could have fallen here in Laval," Transport Minister Michel Despres said.

As a precaution, the government also announced that it shut down another overpass in the Laval area with a similar design over fears that it too could collapse. That structure, like the one that crumbled Saturday, was built in 1970.

Transport Quebec was notified about an hour before the accident Saturday that a chunk of concrete measuring 38 centimetres by 18 centimetres had fallen from the overpass. Despres said an inspector was sent out and found nothing to indicate the structure should've been shut down.

The viaduct collapsed four minutes after the second chunk fell off.

To ensure the rest of the province's overpasses were safe, inspectors worked through the night Saturday, checking all of Quebec's 4,500 overpasses and bridges. They found that 20 need close review.

Saturday's deadly collapse was the second such incident in Laval in six years. Laval Mayor Gilles Vaillancourt tried to ease tensions Sunday, but also acknowledged motorists' worries.

"There is no indication this could happen on another structure," he said. "All the analyses are telling us it is probably something that was not predictable that happened."

"Everybody is going to live with a certain nervousness."

---