One driver allegedly stabbed another on Monday on a gridlocked side road that was being used to divert traffic around a fatal highway crash north of Toronto, police said.

The man, who was stabbed inside his car at about 3:30 p.m. ET, was airlifted to hospital with life-threatening injuries, Ontario Provincial Police said. South Simcoe Police Service said they have a man in custody.

A fatal accident on Highway 400 on Monday took place midway between highways 88 and 89.
(Dwight Friesen/CBC)

Neither police force would confirm if the stabbing was a case of road rage caused by traffic headaches.

The stabbing took place on Canal Road, an arterial road being used to divert motorists around the scene of a late morning tractor-trailer crash that closed a section of Highway 400, about 30 kilometres south of Barrie. 

The highway was closed in both directions between highways 88 and 89 on Monday, and was not expected to reopen until late evening.

Witnesses told CBC News they saw three cars speeding north on the highway at about 11:20 a.m. ET. One of the cars cut off a tractor-trailer, which lost control, hit a guard rail and then rolled into the east ditch.

Tina Lyn Hannahson saw the accident and called the truck driver a hero because he appeared to swerve in order to spare the other cars in his path. He was pronounced dead at the scene.

"He saved everyone's life,"  Hannahson told CBC News.

Police did not release his name Monday.

Ontario Provincial Police have taken two of the drivers involved in the crash into custody.

"Two young men have been arrested for dangerous driving causing death," said Sgt. Cam Woolley.

The two men know each other, CBC News has learned.

Police looking for third driver

Police are still looking for a third driver, who is a "person of interest," Woolley said.

He said the force of the crash scattered debris from several vehicles across all northbound and southbound lanes.

Fire crews cut through the middle guardrails along parts of the highway to allow hundreds of vehicles to turn around.

In another collision over the weekend on the same highway, two people were charged with dangerous driving and criminal negligence after a multi-vehicle crash police believe may have been caused by street racing. Eleven people were injured.

"In the summer, we see a trend with this. We see more injuries and more fatalities from high speeds than we do at any other time of the year," said Woolley.

The highway safety division is trying to figure out how to tackle the increase in speed-related crashes, Woolley said. The number of officers on the road has risen, he added.

With files from the Canadian Press