CN spokesperson Julie Senecal said the cars were all carrying grain and were part of a train that was heading west from Winnipeg to Edmonton on Saturday afternoon.
Senecal said 31 cars left the tracks about 30 kilometres from Wainwright near the community of Fabyan, and 17 fell off the bridge.
"There were no injuries and there are no environmental issues," Senecal said.
According to the town of Wainwright's website, the bridge is almost 60 metres high and 845 metres long. The website says it is Canada's second-longest trestle, with the longest being further south in Alberta at Lethbridge.
George Duffy, who lives near the bridge, said the cars didn't fall from the highest part of the bridge. But he said it was still a "very high" spot and that the cars are so badly damaged they're barely recognizable.
"They're definitely beat up. By looking at them on the ground it's really hard to tell they're railway cars," said Duffy, who notes the frozen Battle River underneath the structure is popular with snowmobilers like himself.
"I've been here going on 23 years, and I've never thought about a train going off the trestle," he added.
He said there's also a lot of grain on the snow around the wreckage.
It's the third train to derail in Alberta in a week.
On Friday, 18 cars went off the tracks near Hay Lakes, southeast of Edmonton.
Earlier last week, a CN freight train derailed between Hinton and Grande Cache.
There were no injuries in the Hay Lakes derailment but one crew member was hurt in the Hinton derailment.
Senecal said the cause of Saturday's derailment near Fabyan is still under investigation.
She said CN is re-routing traffic to a line further north.
"It's too early at this stage to say when the line will be reopened to traffic," she said.
The bridge originally opened in 1909, and according to the town Of Wainwright's website, a man was required at that time to walk the entire length prior to each train crossing.
While images of trains falling car-after-car from blown-up bridges are common in old movies, Senecal explained that the weight of the cars usually snaps the couplers and keeps that from happening.
"You have one car that falls, and very soon you have another, but pretty soon the coupler is going to break," she said.