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

itoggle caption Justin Sullivan/Getty Images

Monday, as a train on an unaffected track passed by (in the background) work continued on removing the commuter cars that derailed the day before. Mark Lennihan/AP hide caption

itoggle caption Mark Lennihan/AP

Passengers move away from Asiana Airlines Flight 214 on Saturday in San Francisco. This photo was taken by a passenger. Eugene Anthony Rah/Reuters/Landov hide caption

itoggle caption Eugene Anthony Rah/Reuters/Landov

A car driven by a 19-year-old man crashed into a tree in Bates Township, Mich., in April. The Iron County Sheriff's Department said investigators believed the driver, who survived the crash, was drunk and speeding. AP hide caption

itoggle caption AP

Pieces of damaged electrode coils from a battery cell that resulted in a fire aboard a Japan Airlines Boeing 787 Dreamliner airplane at Logan International Airport in Boston. Saul Loeb /AFP/Getty Images hide caption

itoggle caption Saul Loeb /AFP/Getty Images