Updated 04/28/15 – 5:07 p.m.

CHICAGO (CBS) — The National Transportation Board has blamed last year’s Blue Line derailment at O’Hare International Airport on operator fatigue and design flaws with the terminal’s automated braking system.

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“The layers of protection that were designed to prevent such an accident failed,” NTSB Chairman Christopher Hart said at a hearing Tuesday morning in Washington.

Hart pointed to the trip arms and bumping posts at the O’Hare terminal at the end of the tracks, saying neither could adequately slow or stop the train, after the operator nodded off while pulling into the terminal. The train was going approximately 26 mph as it pulled into the station on the center track.

When the operator failed to hit the brakes as the train pulled in to the O’Hare terminal, and the automated braking system could not stop the train, it jumped the tracks, and smashed into an escalator.

“Fortunately, nobody was on the escalator at the time of the accident, which occurred at about 2:49 in the morning. If this accident had occurred a few hours later, during rush hour, it could have had far more tragic results,” Hart said.

The operator, Brittney Haywood, has been fired, after acknowledging to investigators she had fallen asleep at the controls.

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NTSB investigator Steve Jenner mentioned the CTA’s scheduling and Haywood’s own choices as factors in her lack of sleep.

“She had participated in recreational sports, rather than trying to sleep before the start of her next shift. This resulted in her getting less than one hour of sleep,” he said.

Hart said Haywood told investigators she was on her 12th straight day of work; some on day shifts, some on night shifts.

“To its credit, CTA has revised its work rest policy since the accident,” Hart said.

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.

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

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Train operators union president Ken Franklin says he hasn’t seen the report yet and therefore can’t comment today.