(CNN) -- The driver was asleep at the controls when a commuter train barreled through the protective end bumper of its stop at Chicago's O'Hare International Airport earlier this week -- but two backup systems should have saved the train, the NTSB said.
The operator of the Chicago Transit Authority Blue Line train jolted awake just in time for her to see the lead car climb the stairs that started not far from where the track ran out, investigator Ted Turpin from the National Transportation and Safety Board said Wednesday.
That was 2:52 a.m. Monday, when most people were in bed. No one was killed, and of the 32 injured, none suffered serious harm.
But emergency braking systems should have stopped the eight-car train without her, Turpin said. The driver is a relatively new employee and has been operating trains for just 60 days, the NTSB said.
It wasn't the first time she has dozed off at the controls, she told investigators. Turpin said she was "very forthcoming" in her admissions. In February, she slightly overrode a station, leaving the train partially past the platform.
Investigators are checking surveillance video to see if she overshot prior stations.
"She dozed off prior to entering the station," Turpin said. "She did not awake again until the train hit close to the end of the bumper."
But her apparent lack of sleep wasn't the only failure. If a driver falls asleep and the controls slips out of her hands, the train should stop automatically, Turpin said.
And when the train raced into the airport's station, it hit a trip arm that activated emergency brakes.
"There is an electrical brake, and there's a disc brake system on the train, and there's a third track brake," Turpin said.
The trip arm set off the first two 41 feet away from the bumper. They engaged and should have halted the train on time. But they didn't.
Investigators are inspecting the tracks' and trains' systems to determine why not.