When do Utah drivers need chains on their tires?

BIG COTTONWOOD CANYON — The crash that injured Brittany Kidd happened just two weeks ago, during one of the first winter storms of the season.
As a canyon patrol driver for the Utah Department of Transportation, Kidd rescues stranded drivers and helps maintain roads in Big and Little Cottonwood canyons.
During a snowstorm in Big Cottonwood Canyon on Nov. 17, she was following snowplows near the Donut Falls Trailhead when another driver steered around the plows, lost control of the vehicle