A single car accident briefly snarled traffic on I-55 just south of the 6th Street split just after 3:00 Monday afternoon.
State Police say a Ford Explorer with two occupants, neither of whom have been identified, attempted to change lanes near mile marker 91 south of the split, but over corrected when attempting to switch back and smashed through a frontage road fence.
The car overturned and continued into a ditch, ejecting both the passenger and the driver.
Sangamon County Coroner Cinda Edwards says one person was pronounced dead a short time later at a Springfield hospital; the other person suffered serious injuries.