A defect not visible to the naked eye is being blamed as the cause of a train derailment in southern Wisconsin over the weekend.
The Canadian Pacific train carrying crude oil from North Dakota jumped the tracks in Watertown on Sunday, with 13 cars derailing. More than 500 gallons of crude oil were spilled and about three dozen homes had to be evacuated from more than a day.
The company said it inspects its lines with a rail flaw detector at least three times a year. The process uses ultrasonic technology to check for defects. The section of track in Watertown was last checked in late September and no issues were found at that time.