A crash involving more than 40 vehicles has snarled traffic on I-84 in Meridian, Idaho on Thursday near the Ten Mile Road exit.
The westbound lanes of the highway are completely shut down.
But there are traffic problems on the east side, too, reported KTVB.
At least 10 people are injured, according to Idaho State Police.
Troopers were clearing a crash when fog hindered visibility, prompting a series of crashes.
Firefighters have had to cut into at least one car to rescue victims.