Heavy fog and ice were to blame.
That according to Wisconsin police who say the multi-vehicle pile up on Friday was due to poor weather conditions.
Around 15 people were treated for non-life threatening injuries after the crash.
The U.S. Highway 41 near Oshkosh was closed for several hours after this.
And it's a similar story across the Prairies. Especially in southern Saskatchewan.
The thick fog did improve throughout the day, but as temperatures drop overnight, poor visibility is expected to return. If you plan on travelling tomorrow, be sure to check the road conditions first. If the fog persists it will be very difficult see, making it dangerous to get around.
For the latest details on what's happening in the Prairies, tune into The Weather Network on TV. Your National Forecast comes up at the top and bottom of each hour.