He somehow lost control of his car and slammed into a wall. That impact ejected him.
The driver is now hospitalized in serious condition.
State Police Master Sgt. Joe Stangl said the 20-year-old was driving south on the expressway shortly after midnight Tuesday when his car door flew open. As he struggled to pull the door shut, the car struck a wall by the 25th Street bridge, and the man was ejected.
Stangl said the man fell about 125 feet and landed in a rail yard below the bridge, but he was still conscious and able to talk to officers on the scene.
Stangl says the man was taken to Stroger Hospital, but his injuries did not appear to be life-threatening.
The Associated Press contributed to this report.