WASHINGTON — Federal investigators were testing the automated controls for Washington D.C. transit trains Wednesday, hoping to figure out why the computerized system designed to prevent collisions failed in a deadly crash this week.

At the time of the crash, the train was controlled primarily by computer, but there is evidence that the operator tried to slow it down.

"What we're trying to understand is how the automatic train control system works and if there were any faults," said Debbie Hersman of the National Transportation Safety Board told CBS' "Early Show." "Today is the first day that we're going to have access to the signal system and the tracks and the circuits to be able to test those."

It wasn't clear when results of the tests would be available, but the board scheduled a late afternoon news conference Wednesday.

The crash Monday occurred just after a train operator, who had been on the job about three months, started her shift. About eight miles down the red line track, another train was stopped. In the blink of an eye, the trailing train, slammed into a stopped one and jackknifed violently into the air, falling atop the first. Nine people were killed, including the train operator, and more than 70 were injured.

"It was only a split second," said 20-year-old Jamie Jiao of Vienna, Va., who was aboard the moving train, sitting just a few feet from where the car was smashed. "We were probably traveling pretty fast. No one had time to react."

Investigators are trying to find out why the train didn't stop, even though officials say the emergency brake control was pushed down and there was evidence that the operator tried to slow her car before impact.

"That train was never supposed to get closer than 1,200 feet, period," said Jackie Jeter, president of a union that represents Metro workers.

Emergency brake controls are referred to as "mushrooms" on transit trains, protruding from the operator's console so they can be slammed down with a swift slap of the palm.

Hersman said Tuesday it wasn't clear when the button was pressed or how it got that way. Much on the train, including toggle switches and other controls, could have been disturbed in the crash, she said.

Safety officials also are investigating maintenance records and a passenger's statement that the train had stopped briefly then started again before the accident.

The horror of the worst disaster in the system's 33-year history shocked the Washington region, where the Metro system is an integral part of the economic and social fabric.