The N.W.T. Department of Transportation says part of the Sahtu winter road system is closing Friday because drivers ignored its daytime closure.

The section between the Deline junction and Wrigley will close for the season as of 11 a.m. Friday.

On Tuesday the winter road was restricted to night-time traffic only, but an inspector found four trucks travelled on the road during the day despite the closure.

Fred Lamb, the N.W.T.’s manager of highways, said the trucks severely damaged the road and it’s irreparable for this season.

"It's not so much the temperature, but the strength of the sun's rays change the composition of the snow — it starts to break down and it doesn't have the loading strength," he said. "So the vehicles — both light and heavy — break through the snow pack and start rutting into the ground underneath."

Lamb expects all Deh Cho and Sahtu winter roads, with the exception of the Nahanni Butte access road, to close on Sunday.

Travel on the Mackenzie Valley winter roads and the Trout Lake winter road are restricted to night time only. Any vehicles on the winter road after 11 a.m. are required to park and not move until the road reopens at 10 p.m.

He said driving on a closed road could damage the tundra underneath the ice and make it difficult to build the winter road next year.

Lamb said the department will put up barricades for any section of road that's closed. Anyone caught driving on a closed winter road will be fined $800.