UPDATE 9:58 a.m.:
All lanes now open on Highway I-43 SB at University Avenue.
According to Green Bay Police, a man died in the crash. The man has not been identified. The driver is cooperating with officers.
Police still don't know why this happened and they don't know exactly where the victim was when he was hit.
PREVIOUS: A portion of I-43 Southbound from University Avenue to East Mason Street is closed due to a fatal crash.
The Green Bay Police Department is investigating.
It's unknown how long the area will be shut down.