OPP Sgt. Kerry Schmidt said the QEW is icy, particularly through Burlington, Oakville and Mississauga.
He said the area between Dorval Drive and Trafalgar Road is a "just skating rink."
"People still need to drive with extreme care," said Schmidt. "Hopefully people are getting used to the fact that their travel times will be longer than normal.
"People just need to exercise caution and adjust their driving as road conditions change."
Early Thursday, a tractor trailer jackknifed near Highway 403, leading to a delay that was cleared before 6 a.m.