The Chicago Transit Authority restored Blue Line service between the O'Hare and Rosemont stations on Sunday, following a train derailment at O'Hare International Airport on Monday.
Rail service was restored around 2 p.m.
Service at the O'Hare station has been disrupted for almost a week after a train derailed, sending rail cars onto an escalator at the station.
The eight-car train jumped the tracks and landed on the stairs and escalators leading to the airport terminals just before 3 a.m. Monday. The crash left 32 people injured, and three passengers have since filed lawsuits against the CTA.
The National Transportation Safety Board estimates the crash caused about $6 million in equipment damage.
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"CTA personnel have worked around the clock in recent days to repair the O'Hare Blue Line Station," CTA said in a statement.
The NTSB said the operator admitted to dozing off at the controls as the train pulled into the station.
"She did not awake again until the train hit close to the end of the bumper," investigator-in-charge Ted Turpin said.