ISP responded just before midnight to southbound I-57 near 99th Street and Chicago's Longwood Manor neighborhood for a report of a pedestrian who had been hit.
The individual was taken to a local hospital with life threatening injuries, police said.
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Just before 12:55 a.m., the southbound lanes of I-57 near 99th Street were closed for an investigation. All lanes reopened just before 5 a.m.
The person hit has not been publicly identified, and information about any possible charges was not immediately available.