BISMARCK, N.D. - Federal investigators said Wednesday they have recovered a broken axle at the scene of an oil train derailment and fire in southeastern North Dakota but don't know yet whether it caused the wreck.
"We'll want to know if it was the actual cause of the derailment, or was it broken during the derailment?" National Transportation Safety Board member Robert Sumwalt said.
Investigators at the scene have found nothing wrong with the railroad track or with signals along the tracks. Interviews of train crews were to begin as early as Thursday, Sumwalt said, and investigators have other work to finish such as developing a detailed timeline of the incident and going through shipping records.
"Our investigative teams will be here through the weekend," he said. "We are in the very early stages of the investigation, but even still we are making good progress."
The NTSB said earlier that a westbound BNSF Railway train carrying grain derailed first Monday afternoon, and a portion of it fell onto an adjacent track carrying the eastbound BNSF oil train. Eighteen cars on the 106-car oil train derailed and several burned. No one was hurt, but many of the 2,400 residents in nearby Casselton temporarily evacuated due to potentially unsafe air.
Investigators have determined that the grain car derailment happened at a point in the tracks where a train can be switched to a side rail, Sumwalt said.
"We believe it to be a very short window," he said of the time that elapsed between the grain train derailing and colliding with the oil train. "Not a matter of minutes but something probably less than a minute. We think it was very quick."
Residents of Casselton were welcoming a return to normalcy Wednesday while railway crews spent New Year's Day working in subzero weather to get the track ready to reopen Thursday.
Mayor Ed McConnell was back at his trucking business, finishing year-end work he said he typically completes the day before the holiday.
"It's like taking a day and a half out of your life," he said of the disruption caused by the derailment.
Earlier, McConnell called for federal lawmakers to address safety concerns posed by transporting oil by rail.
"There have been numerous derailments in this area," he told The Associated Press. "It's almost gotten to the point that it looks like not if we're going to have an accident, it's when."
While the rate of oil train accidents remains low, there has been a sharp increase in the past several years in the number resulting in accidental releases. That increase is being driven by a surge in drilling in North Dakota and other western states.
Casselton's voluntary evacuation recommendation was lifted Tuesday afternoon after air quality tests, and a Red Cross shelter set up at the high school was shut down.