National Transportation Safety Board member Mark Rosekind made that announcement at a news conference Saturday. He said the signals had been activated seven seconds before the float crossed the tracks.
Four veterans of Iraq and Afghanistan were killed Thursday when a freight train slammed into the parade float in Midland. Sixteen people were injured.
Rosekind said the NTSB reconstructed the accident using video cameras from the train and a sheriff's vehicle.
He said the train started sounding its horn nine seconds before it hit the float. The train engineer also used the emergency brake five second before the crash.
(Copyright 2012 by The Associated Press. All Rights Reserved.)