Investigators and first responders work near the wreckage of Amtrak Northeast Regional Train 188, which derailed May 13, 2015, in north Philadelphia. Eight people were killed and hundreds injured in the crash. Win McNamee/Getty Images hide caption

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A photo of the truck that hit and shifted the train tracks, causing an Amtrak derailment in Kansas. National Transportation Safety Board via Twitter hide caption

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Smoke inhalation victims walk past a firefighter towards a medical aid bus Monday after passengers on the Washington, D.C., subway were injured when smoke filled the L'Enfant Plaza station during the afternoon rush hour. Paul J. Richards/AFP/Getty Images hide caption

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National Transportation Safety Board Chairman Deborah Hersman briefing reporters about the July 2013 crash of Asiana Airlines Flight 214 in San Francisco. Justin Sullivan/Getty Images hide caption

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