A convoy of evacuees have begun the long drive out of work camps north of the fire-ravaged Fort McMurray area.
Meanwhile, a mass airlift of evacuees was expected to resume, a day after 8,000 people were flown out.
In all, more than 80,000 people have left Fort McMurray, in the heart of Canada's oil sands, and officials say no deaths or injuries related to the fire have been reported.
Crews battling the fire got a little help with temperatures forecast to fall overnight to 16C (61F) from the low 30s.
The Alberta provincial government, which declared a state of emergency, said more than 1,100 firefighters, 145 helicopters, 138 pieces of heavy equipment and 22 air tankers were fighting the fire, but Chad Morrison, Alberta's manager of wildfire prevention, said rain is needed.
"Let me be clear: air tankers are not going to stop this fire," he said. "It is going to continue to push through these dry conditions until we actually get some significant rain."
Environment Canada forecast a 40% chance of showers in the area on Saturday.
About 25,000 evacuees moved north in the hours after Tuesday's mandatory evacuation, where oil sands work camps were converted to house people. But the bulk of the more than 80,000 evacuees fled south to Edmonton and elsewhere, and officials are moving everyone south where they can get better support services.
Some 8,000 evacuees had been flown to Edmonton and Calgary by Thursday night. It appeared the highway is safe enough on Friday to move thousands more south on the highway.
Officials said a helicopter would lead the evacuation convoy on Friday morning to make sure the highway is safe.
The convoy will pass through Fort McMurray where the fire has torched 1,600 homes and other buildings. The Royal Canadian Mounted Police is escorting 50 vehicles at a time.
Fort McMurray is surrounded by wilderness, and there are essentially only two ways out via road.
Aided by high winds, scorching heat and low humidity, the fire grew from 75 square kilometres on Tuesday to 100 square kilometres on Wednesday, but by Thursday it was almost nine times that - at 850 square kilometres. That is an area roughly the size of Calgary, Alberta's largest city.
Unseasonably hot temperatures combined with dry conditions have transformed the boreal forest in much of Alberta into a tinder box.
Mr Morrison said the cause of the fire has not been determined, but he said it started in a remote forested area and could have been ignited by lightning.
The region has the third-largest reserves of oil in the world behind Saudi Arabia and Venezuela.