The driver saw a man with dreadlocks who had a black handgun driving a blue minivan, police said. The license plate began with the letter Q.
Officials said a vehicle was damaged in the shooting but no injuries were reported. Troopers walked the southbound lanes looking for shell casings for about an hour after the shootibng.
The expressway reopened shortly before 6 p.m.
The Sun-Times Media Wire contributed to this report.