The crash occurred just before 2:30 a.m. at 18th Street in the southbound lanes of the Dan Ryan.
Troopers said there was a minor traffic crash on the expressway between two cars and the victim got out of one of the vehicles involved.
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The victim, a woman, was then hit by another vehicle that was not involved in the original crash, according to ISP. The Cook County Medical Examiner's Office later identified her as 30-year-old Stephanie N. Johnson.
Police said the driver who struck Johnson did stop at the scene.
The crash caused major delays during the morning rush hour. All four southbound lanes were closed down in the area for more than four hours, with traffic being diverted onto I-55. All lanes reopened just before 7 a.m.
It is unclear if any citations will be issued. Police said the crash is under investigation.