Two westbound lanes on the Queen Elizabeth Way in Mississauga were due to reopen Monday evening after a tractor-trailer rolled over hours earlier near Royal Windsor Drive.
The Ontario Provincial Police said the crash occurred at around 1p.m.
The driver was trapped, but then freed and taken by air ambulance to Hamilton General Hospital with life threatening injuries.
All lanes on the highway were closed in the immediate aftermath of the crash.
The eastbound lanes later reopened, but the ramp at Royal Windsor Drive and all westbound lanes were expected to remain closed until the evening.