Semi Jackknifes on Icy Mountain Curve, Blocking Entire Roadway Gallatin County, MT — A dash-cam video captured a heart-stopping moment on a narrow mountain pass Wednesday afternoon when a semi truck lost traction on an icy downhill curve, jackknifed, and skidded sideways across both lanes, leaving oncoming drivers with only seconds to react. The footage shows the long trailer swinging out like a pendulum as the truck’s cab slides toward the outside edge of the roadway, spraying snow into the air