By 3 p.m., the lanes reopened after about an hour and a half. A witness reported a shootout on the expressway between people in two vehicles.
No injuries were reported, police said.
During the closure, investigators searched for evidence between Independence and California as some stuck drivers turned around and funneled off the expressway via the on-ramp at Homan.
A motive for the shooting was not determined, but many recent expressway shootings result from neighborhood violence spilling out onto the expressway.
No one was in custody.
Anyone who witnessed the shootout or has information about the incident is asked to call state police at 847-294-4400. Callers may remain anonymous.