The problem near the Rosemont station caused delays of up to 20 minutes during the morning rush hour, officials said.
Preliminary information indicates that a rail car trolley shoe — a component that connects the train with the third rail — made an improper connection with the third rail, which caused the rail to lift and then be pushed over as other rail cars traveled through the section," CTA spokeswoman Catherine A. Hosinski wrote in an email.
No workers or customers were endangered by the mishap, she added.
The CTA took to Twitter to warn customers about the problem shortly after 8 a.m. and service was not restored until just before 11 a.m., officials said.
The CTA offered round-trip shuttle trains between Rosemont and O'Hare stations for passengers hoping to avoid the wait, according to the agency.