New mystery in train crash:

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PHILADELPHIA — The Amtrak train that derailed along the nation’s busiest tracks may have been struck by an object in the moments before it crashed, investigators said Friday, raising new questions about the deadly accident.

PHILADELPHIA — The Amtrak train that derailed along the nation’s busiest tracks may have been struck by an object in the moments before it crashed, investigators said Friday, raising new questions about the deadly accident.

National Transportation Safety Board member Robert Sumwalt said an assistant conductor aboard the train told investigators that she heard the Amtrak engineer talking over the radio with an engineer for a regional railroad just before the crash.

The regional engineer, who was in the same area as the Amtrak train, said his train had been hit by a rock or some other projectile. The conductor heard Brandon Bostian, who was at the Amtrak controls, say the same had happened to his train, according to Sumwalt.

The windshield of the Amtrak train was shattered in the accident but one area of glass had a breakage pattern that could be consistent with being hit by an object and the FBI is investigating, he said.

Sumwalt declined to speculate about the exact significance of a projectile, but the idea raised the possibility that the engineer might have been distracted, panicked or even wounded in the moments before the train left the rails at more than twice the speed limit along a sharp bend.

Bostian told investigators that he does not recall anything after ringing the train’s bell as he passed by the North Philadelphia station a couple of minutes before Tuesday night’s crash.

NTSB spokesman Peter Knudson said the board was seeking more information about a third report of damage that night, this one involving a different Amtrak train.

Not long before the derailment, two passengers on a southbound Amtrak told The Philadelphia Inquirer that something shattered a window on their train as it passed through the same area. They said Amtrak police boarded the train at 30th Street station in Philadelphia to document the incident.

The derailment has made it clear that despite the train industry’s widespread use of electronic signals, sensors and warning systems, safety still sometimes comes down to the knowledge and experience of the engineer.

Those skills would have been critical on the curve where the New York-bound train derailed, killing eight and injuring more than 200 in the deadliest U.S. train accident in nearly six years.

Instead of high-tech signals or automatic controls, engineers on that stretch of track have to rely on their familiarity with the route and a printed timetable they carry with them, not unlike engineers a century ago.

“We’re depending heavily on the human engineer to correctly obey and interpret the signals that he sees and also speed limits and other operating requirements,” said David B. Clarke, a railroad expert at the University of Tennessee.

The engineer, who had been working that route for several weeks, said in an NTSB interview Friday that he felt comfortable with the train and was not fatigued, Sumwalt said.

In the minute before the derailment, the Amtrak train accelerated from 70 mph to more than 100 mph, even though the curve where it came off the tracks has a maximum speed of 50 mph.

It’s not clear whether Bostian manually accelerated, Sumwalt said, though a data recorder shows that he did engage a braking system seconds before the derailment.

Experts say the railroad’s signaling system would have slowed the train automatically if it had hit the maximum speed allowed on the line, but older cab-signal and train-control systems do not respond to localized speed restrictions.

Investigators are also conducting drug tests. Bostian’s lawyer has said he was not using drugs or alcohol.