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Warning Signals Activated 7 Seconds Before Veterans Crossed Train Tracks

Joseph Devenney/Getty Images(MIDLAND, Texas) -- The warnings signals at a railroad crossing were activated seven seconds before a flatbed truck full of wounded veterans crossed the tracks during a parade and was struck by a freight train, according to preliminary details released by the National Transportation Safety Board.

Four veterans were killed and 16 were injured in the accident, which happened on Thursday.

It is not yet clear when the train conductor applied the brake, but the question is one of dozens the board hopes to answer in the coming weeks.

"Our mission is to determine probable cause, which is to determine not just what happened but why," NTSB Board Member Mark Rosekind said. "And that why is critical for us to determine what safety recommendations need to be issued so this does not happen again."

Investigators will be on scene in Midland for seven to 10 days collecting evidence to bring to Washington, D.C., for processing. They will examine both vehicles and the gates that should have blocked the tracks. They will also contact all drivers, victims and witnesses.

Given that the area where the crash happened is a "quiet zone," Rosekind said his team will be looking into whether that played a role in the collision.

Copyright 2012 ABC News Radio

ABC News Radio