In a final report on the 2012 derailment, the National Transportation Safety Board said a broken rail was responsible. The agency said there was evidence of "gradual deterioration of the rail-head surface."
Rose Louese Mayr and Elizabeth Conway Nass, both 19-year-old college students, were sitting on the bridge, which carries CSX tracks over a street in Ellicott City, at the time. The report said their actions "placed them in harm's way," but did not cause the crash.
The crash on Aug. 20, 2012, sent 21 cars off the tracks. One overturned, burying Mayr and Nass under coal and seven fell into a parking lot.
The report found that CSX had been testing the rail line more frequently than federal regulations demanded. The NTSB said the company was concerned about a history of problems in the area and an increase in the amount of coal being shipped.
Ellicott City is an affluent community about 10 miles west of Baltimore on the Patapsco River. The derailment and cleanup shut the town down for several days.