A CSX coal train derailed on a railroad bridge in Ellicott City, Maryland, just before midnight on August 20, 2012.
Elizabeth Nass and Rose Mayr, both 19, were killed "when coal spilled out of the rail cars during the derailment."
The train had been traveling 23 mph, and the first 21 of the 80 cars in the train derailed. Seven cars fell into a parking lot.
"The presence in the rail right-of-way of the two fatally injured persons, whose unauthorized access placed them in harm's way, did not contribute to the derailment in any way," the board said.
"The NTSB investigation found that the point of derailment was a rail fracture several hundred feet before the bridge. The section of rail, which was examined in the NTSB's materials laboratory in Washington, showed evidence of rolling contact fatigue, a gradual breakdown of the rail-head surface."
The derailed train also damaged fiber-optic lines and temporarily disrupted Internet service at the U.S. naval base at Guantanamo Bay, Cuba, delaying the trial for Khalid Sheikh Mohammed and four others facing terrorism charges this week, a base spokesman said at the time.
The facility lost about 50% of its connectivity, which is serviced by satellite downlink locations in Maine and Maryland.
The Federal Railroad Administration started a Rail Failure Working Group "to study the effects of rail-head wear and resulting rail surface conditions" as a result of this and other incidents.
The Rail Safety Advisory Committee adopted its recommendations in April. CSX put a chain-link fence on the right-of-way in an effort to halt trespassing.
There will be a public forum in 2015 "to explore and educate the public about the dangers associated with unauthorized individuals in the railroad right-of-way."