CHICAGO (CBS) — The derailment of a CTA Blue Line train near O’Hare International Airport on Wednesday seems to have been the result of human error, after the motorman apparently made a minor operating mistake and over-corrected, according to a source familiar with the investigation.

The derailment happened around 7 p.m. Wednesday in the tunnel approaching the O’Hare terminal, causing major delays for several hours.

A source familiar with the investigation into the cause of the derailment said the train’s motorman appeared to have made a minor operating error, realized the mistake, and over-corrected, causing the train to derail. An apparent miscommunication between the CTA control tower and the motorman also was a contributing factor.

A CTA Blue Line train derailed in the tunnel approaching O‘Hare terminal on April 10, 2019. (Credit: Connor L)

The source said there was no “infrastructure element” involved, meaning no mechanical issues with the train, tracks, or switches.

There also is no sign at this point any alcohol or drug use was involved.

A total of 73 passengers were evacuated from the train after the derailment. A 39-year-old woman was taken to Resurrection Medical Center with a back injury, Chicago Fire Department officials said.

(Credit: Glyn Garside)

Blue Line trains did not run between Rosemont and O’Hare for nearly seven hours after the derailment, and the CTA provided shuttle buses from Rosemont to the airport. Normal service resumed around 2 a.m. Thursday.

Human error also was to blame for a major Blue Line train derailment at the O’Hare platform in 2014, when the train’s motorman admitted she “nodded off” as the train was entering the station. The train jumped the tracks, and smashed into an escalator at the end of the terminal.

The operator, Brittney Haywood, was fired after acknowledging to investigators she had fallen asleep at the controls. Haywood told investigators she was on her 12th straight day of work; some on day shifts, some on night shifts.

However, the National Transportation Safety Board also found a design flaw contributed to the crash, noting the trip arms and bumping posts at the O’Hare terminal at the end of the tracks could not adequately slow or stop the train after the operator nodded off while pulling into the terminal.

This CTA train smashed into the escalator on Monday morning at the O’Hare station. (Credit: CBS)

The CTA also has since lowered the speed limit on its O’Hare platforms from 25 mph from 15 mph, and moved the trip arm farther from the bumper post, to give trains more room to stop. The CTA also revised its work rest policy to give motormen more time between shifts.

More than 30 people on the train were injured in the 2014 derailment, and the crash caused more than $9 million in damages to CTA property.