The CTA Blue Line operator who was driving the train that crashed at the O’Hare stop early Monday morning had been operating trains for only about 60 days and had fallen asleep at the controls before, a federal investigator said Wednesday.

National Transportation Safety Board investigator Ted Turpin said in February she dozed off and overrode a station so that some of the doors were past the station. The CTA became aware of the incident and she was put on a progressive discipline system. There was also an instance where she overslept and was late for work.

The operator was hired by the CTA in April 2013 and began operating trains in January of this year. She began working Sunday evening around 10 p.m. and was on her fourth of five round trips between Logan Square and O’Hare when the accident occurred, Turpin said.

Just before 3 a.m. Monday morning the Blue Line train pulling into the O’Hare station failed to stop and jumped the tracks continuing to the top of an escalator injuring more than 30 people. An emergency track-side braking system activated but failed to stop the train. The estimated equipment damage of the accident is $6 million and does not include any of the structural damage at the station, Turpin said.

Turpin explained the operator’s schedule varied because she worked on a fill-in basis. She admitted to dozing off and said she did not wake up until the train jumped the tracks.

The NTSB will now compare the CTA’s records with the information from interviews and look into areas such as fatigue and work cycles.

Turpin said a preliminary review showed the train was traveling at the correct speed of 25 mph as it entered the station. Investigators said they have not yet determined whether the operator ever applied the in-cab brake. However, he said an automatic emergency braking system located on the tracks was activated but failed to stop the train as it burst onto the platform.

The train is designed to stop if operators become incapacitated and their hand slips off the spring-loaded controls. Kelly speculated that, upon impact, inertia might have thrown the operator against the hand switch, accelerating it onto the escalator.

The operator, whom officials have not identified, was off duty for about 17 hours before starting work around Sunday evening but had recently put in a lot of overtime, Amalgamated Transit Union Local 308 President Robert Kelly said Monday.

The operator took standard drug and alcohol tests after the derailment and that she assured him they were not an issue, Kelly said.

Investigators have also been scrutinizing the train’s brakes, track signals and other potential factors while reviewing video footage from more than 40 cameras in the station and on the train, Turpin said.

The station remained closed Wednesday with shuttle basses in place between O’Hare and Rosemont. CTA officials have not said when full Blue Line service will resume at O’Hare.

Also Tuesday, attorneys for one of the injured passengers filed a negligence lawsuit in Cook County court against the CTA seeking more than $50,000 in damages. A CTA spokeswoman said the agency doesn’t comment on pending litigation.