Freezing rain turned into sheets of treacherous ice, forcing Idaho and Montana highway officials to shut down part of Interstate 90 most of Monday night.
After 15 semi-tractor trailers slid into ditches or jackknifed near Lookout Pass, a 10-mile stretch of I-90 was closed from Wallace to the border.
All eastbound freeway traffic was diverted through Wallace to other roads.
Authorities expected to open the pass late Monday night after sand trucks were called to the scene and tow trucks removed stranded vehicles.
In Missoula, a Montana Highway Patrol dispatcher said 40 to 50 cars had slid off the road since road ice began forming in late afternoon.
A Montana Department of Transportation dispatcher said an eastbound tanker truck slid off the road, hitting several cars.
None of the aviation fuel tanks ruptured and no one was hurt, she said.
Montana workers shut down about 12 miles of the interstate east of Lookout Pass, said a transportation department worker.
“It’s so slick there even our snow plows have had to chain up,” she said.
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