The Wisconsin State Patrol shut down westbound I-39/90 at Hwy 26 in Janesville at 4:48 a.m. due to a semi-truck accident near mile marker 168.
The Rock County Communications Center said the semi-truck jackknifed and is blocking all northbound lanes.
Drivers were unable to use the northbound ramp to the interstate at the Milton Avenue interchange until police cleared the accident around 6:30.
Officials initially worked to clear a shoulder of the interstate to allow the stuck traffic through, but they asked drivers to take alternate routes.
Northbound drivers were directed off of the interstate at Highway 14/Humes Road and detoured to take Highway 51 north.
