At a press conference today, NTSB investigator Debbie Hersman noted that the agency will also look at the actions of on-board operators. "We don't know, at this point, whether the operator could have seen ahead of them in time to stop," she said.

The striking train included cars that are some 30 years old ready for replacement, which raises the possibility of a mechanical failure. The NTSB said it also plans to examine cell phone and text messaging records of the operators, as well as signal systems and tracks.