The Canadian National Railway has announced that the Memorial Day train derailment in Potterville was caused by a broken railroad track.
The community's 2,200 residents were evacuated for four days wile the derailed train was removed. Several of the cars contained explosive liquid propane and toxic sulfuric acid.
Canadian National says there was a fracture inside the rail that was undetectable when federal inspectors visited the track a few days before the derailment. CN inspectors also didn't spot the problem in their twice-weekly inspection.
The Federal Railroad Administration is still investigating the derailment.