FOREST PARK, Ill. (AP) — The morning commute was mainly running smoothly a day after an empty, unmanned commuter train slammed into another at a suburban Chicago station, injuring dozens of passengers.

The Chicago Transit Authority train connecting Chicago's western suburbs with downtown and O'Hare International Airport was operating on a single-track near the Harlem stop on Tuesday. The train was bypassing the station where Monday's collision occurred.

Video footage shows that no one was driving the four-car train when it rumbled the wrong way toward a parked train about 10 miles west of Chicago. Investigators are trying to determine how it somehow started moving along the tracks.

The trains are driven by conductors.

As many as four dozen people on the parked train were treated for minor injuries.

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