Ontario Provincial Police are investigating why a driver decided to reverse his car on Highway 401 late Sunday night -- a move that caused a serious accident and resulted in his death.

"In this situation, I don't know what the reason was. We may never know why he was backing up on a highway that wasn't even shut down," OPP Sgt. Dave Woodford told reporters at the scene. "Maybe he missed his turn and decided he didn't want to go to the next exit."

Authorities say the accident happened at around 11:40 p.m.  in Whitby when a Chevy Impala reversed down the far right lane of the highway's eastbound lanes, just east of Thickson Road.

It collided with a tractor trailer that was unable to swerve out of way in time. The impact ignited the Impala's fuel tank, setting the car in flames. Both vehicles slid to the right side of the road, with the truck going over the ramp and dislodging from the front cab.

The cab fell onto the embankment and rolled onto the Thickson on-ramp when the trailer became lodged on the guardrail not far from a weigh scale. The driver of the truck was not injured.

"I tried to move, but there was nothing I could do. I tried to break, but there was not enought time," Hardeep Padda of Montreal told reporters.

The 76-year-old passenger of the burning car, a visitor from Florida, managed to make it out of the vehicle but suffered severe burns. They were transported to Sunnybrook Hospital with life-threatening injuries.

The 72-year-old driver, an Ajax resident, did not make it out of the car and was pronounced dead at the scene.

"I feel so bad for this guy who died, but it was very bad what he did," Padda said.

The accident left the highway shut down in the area for about five hours.

Police will not release any information about the dead motorist until next of kin are notified.

Witnesses to the crash are being asked to call police at 905-668-3388.

With a report from CTV Toronto's Jim Junkin