Blue Line trains are standing on the Near West Side, after an unauthorized person was on the tracks, the CTA said.
Blue Line trains were standing at Western Avenue just after 3 p.m., the CTA said.
Chicago fire officials said the person who was on the tracks was taken to Stroger Hospital in critical condition.
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It was not immediately clear how the person got on the tracks along the Eisenhower Expressway.
This is a developing story; check back with ABC7 Chicago for updates.