The semi, hauling a load of apples, went over a barrier, and landed on nearby railroad tracks, according to the UHP.
All three occupants a woman and two men were not wearing seat belts and were ejected from the semi, Johnson said.
The woman, Laura Fannin, 26, was taken from the scene by medical helicopter in critical condition. Jirden Mcinvale, 28, who was driving, and Christopher Odom, 39, were transported to a local hospital by ground ambulances, also in critical condition but with non life-threatening injuries, according to UHP.
All three are from Alabama.
All lanes in both directions were closed until about 11:25, when one lane of US 6 was opened for alternating one-way traffic,the Utah Department of Transportation reported.
Troopers finally cleared the crash by 7 p.m. In the meantime, eastbound traffic on US 6 was able to access US 89 to go south toward Thistle and Fairview.
Salt Lake Tribune reporter Michael McFall contributed to this story. firstname.lastname@example.org