A series of collisions involving 21 vehicles happened on Interstate 90 near Hardin, Montana Highway Patrol Sgt. Jay M. Nelson said by email. “A quick-arising dust storm caused a 21-vehicle incident this evening,” he said. Officials did not immediately release information Friday night on possible injuries. Delays on the highway are expected to last for hours, Nelson said. All eastbound traffic was being diverted off the highway, and westbound traffic has been reduced to one lane, according to the Montana Department of Transportation, which first reported about the pileup near mile post 493 at 4:55 p.m.