The QEII Highway south of Edmonton has reopened after a series of crashes that injured 100 people during a storm that dumped as much as 25 centimetres of snow on Thursday.

The aftermath of the chain-reaction crashes closed the highway — the main route from Calgary to Edmonton — until late Thursday night. About 85 to 100 vehicles were involved in the crash near the town of Millet.

About 80 people were treated at the scene by EMS and another 22 were taken to area hospitals.

RCMP said that the most seriously injured person was a man who was struck by a semi-truck while he was standing outside his vehicle after a collision.

About 45 heavily damaged vehicles had to be towed. The CBC’s Briar Stewart reported that most of the vehicles have been cleared away. She said the road is open but slippery.

RCMP investigators are trying to piece together what happened. Since the scope of the crash was so huge, RCMP Corp. Colette Zazulak said that collision reports were not filed at the scene the way they typically are.

Once people file reports with RCMP detachments, investigators hope to get a better picture.

"Which ones happened where, and what vehicles were involved," Zazulak said. "From there, they're going to determine whether it was just nature, in the sense of the conditions, or whether there are any charges to be laid or things like that."

One witness believes a lack of advance signage about the road closure may have caused some vehicles to go into the ditch.

Jim Fyshe said he saw several vehicles go into the ditch along the QEII highway yesterday. (CBC)

Jim Fyshe says he was approaching Leduc when the traffic suddenly stopped. He was able to brake without hitting the driver in front of him, but people behind him weren't so lucky.

"The car behind me wasn't able to do that, and it went off into the ditch," he said. "I looked in my rear view mirror, and I saw three, maybe four, cars further back that had lost control, had gone sideways. There may have been an accident."

"It seemed to me that all of these accidents had been caused by the fact that the highway had been closed off, and nobody had any warning of it, and they couldn't stop in time," he said.

"Because up to that point, the highway really wasn't in that bad of shape. Visibility wasn't terrific, but the actual road surface was in pretty good shape."

Woman and children killed

Another crash north of Edmonton killed three people Thursday — 23-year-old Christine Michaud, her four-year-old niece Hailie Michaud and a two-year-old nephew Trent Michaud.

Eran Peletier, Trent's mother and Hailie's step-mother, was badly hurt as was her son Owen Michaud, 4.

They were in a car that crashed head-on with a truck on Highway 44 halfway between Westlock and Slave Lake.

The driver of the truck, who is facing charges including dangerous driving causing death, was also hurt.

Peletier and husband, Jeff Michaud, had just moved to Slake Lake from New Brunswick six months ago.

Mayor Karina Pillay-Kinnee said they were well-known in the community.

"I think a lot of people will be familiar with them, either in the workplace, or know their families, or the schools, the children," she said.

Within Edmonton, city police dealt with 133 collisions on Thursday, nine involving injuries.

Edmonton cleanup crews worked overnight to clear streets in time for the Friday morning commute.