Engineers are examining the scene of a deadly highway overpass collapse in Laval, trying to determine why a 20-metre section of the bridge gave way over the weekend.

Crews are removing the debris at the site of the collapse, CTV Montreal's Derek Conlon reported Monday.

"Presumably, those pieces may be key to the investigation that's going to be conducted into the collapse of the Concorde overpass, and that's why that was taken away," he said. "Special analysis will be done on those pieces of concrete."

Meanwhile, thousands of Laval motorists and transit users were urged to use public transit after the collapse closed a major expressway linking the suburb to Montreal, jamming other major south-bound routes.

Officials called on commuters who normally use the highway to reach Montreal to switch to public transit and have added extras trains and buses to the regular schedules.

Highway 19, an important north-south link between Montreal and its northern suburbs as well as the Laurentian region, is to remain shut for an indefinite period.

A second nearby Laval overpass has also been ordered closed as a precaution because it also dates from 1970 and is identical in construction to the one that collapsed over the weekend.

"They're taking no chances. The overpass has been closed, and there's no word on when that will reopen," Conlon said.

A third overpass, also located in the Montreal neighbourhood of Outremont, was also ordered closed Sunday.

On Sunday, Quebec Premier Jean Charest vowed to get to the bottom of the overpass tragedy amid concerns the province's public highway infrastructure is unsafe.

"For the time being, it's inexplicable," he told reporters. "I guarantee we will do everything possible to find out what happened. I can only guess how frightening it was for the people involved."

Objections to inquiry appointment

Transport Minister Michel Despres announced that a public inquiry into the tragedy will be led by former Parti Quebecois premier Pierre-Marc Johnson.

"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," Despres said.

There is no word on when that inquiry will begin, but the choice of Johnson as inquiry head has already sparked some protest

Action democratique Leader Mario Dumont objected to Johnson's appointment on Monday, saying he was chosen for all the wrong reasons.

"When you look at the appointment, why Pierre-Marc Johnson, it's hard to find other reasons than the fact that it's a former PQ premier," Dumont said.

"It restrains the room to maneuver, for the Official Opposition to ask questions, and the fact that it's all strategic political communication, it's certainly not the type of preoccupation that we expected our premier to have in a case like this one."

Johnson resigned from his post on the board of directors for St. Lawrence Cement as soon as he was named, CTV Montreal reported.

Johnson has asserted that the law firm of Heenan Blaikie, where he works as counsel, will not pose a conflict of interest.

Johnson held the post of premier from October to December, 1985, when he was defeated by the Liberals.

Disbelief and grief have given way to anger as the cost of the overpass collapse in Quebec finally became clear.

All five victims identified

Five people in two southbound vehicles passing underneath Highway 19 were crushed to death when a massive 20-metre chunk of the three-lane highway overpass collapsed on Saturday.

On Monday, authorities identified the two other people who died in the overpass collapse near Montreal as Veronique Binette and Mathieu Goyette, both of whom were 28. They both lived in Laval.

The three other people killed in the accident have been previously identified as Jean-Pierre Hamel, 40, his partner Sylvie Beaudet, 44, and his brother Gilles, 44.

That couple leaves behind an eight-year-old son Gabriel. His mother had dropped him off at his hockey game just before noon on Saturday and had promised to pick him up just after 2 p.m. Twenty-four hours later, his relatives told him of his parents' death.

Another six adults, four men and two women, were also injured -- two of them critically. Four people still being treated at the hospital are listed as being in serious but stable condition.

Sacre Coeur Hospital officials said at a Monday press conference that the patients suffered spinal injuries, and one patient received hours of brain surgery.

But none appear to have been paralyzed and are expected to make a full recovery. Officials added, however, that while the physical wounds may heal, they're concerned about the mental trauma suffered by the patients from such an accident.

The two cars were removed from beneath the rubble of the overpass early Sunday morning -- 15 hours after they were crushed at 12:37 p.m. Saturday.

Officials review highway system

At a Transport Quebec press conference on Monday, officials said they inspected 18 overpasses across the province that have similar characteristics to the Laval bridge.

However, only one will remain closed. The overpass is located just one kilometer north of the collapsed bridge, and investigators hope it will provide some clue as to why the bridge fell apart.

The Laval overpass was built in 1970 and is owned by the province. Both the province and the city of Laval are responsible for its upkeep.

One man was killed and two others were injured when a highway overpass under construction, also in Laval, collapsed in the summer of 2000.

A coroner's report later concluded a construction company didn't properly secure the concrete beams, and accused the province's construction industry of shoddy work and questionable corporate practices.

At the time, the PQ government came under fire for allegedly lax construction and inspection practices in the province's highway network.

With files from The Canadian Press