The U.S. National Transportation Safety Board said the warning bells and signals at the West Texas track were activated 20 seconds before the accident. The second float didn't go onto the track until several seconds later, just after the guardrail began lowering.
Four veterans of Iraq and Afghanistan were killed Thursday when the train slammed into the parade float in Midland. Sixteen people were injured.
Nine seconds before the crash, the train sounded its horn, a blaring that lasted four seconds, according to NTSB member Mark Rosekind. The guardrail hit the truck, and then the engineer pulled the emergency brake, trying to bring the train to screeching halt.
"Once the crossing becomes active, people should stop," lead investigator Robert Accetta with the NTSB said.
People on the first float and dozens of others who had come out to greet the veterans shrieked and watched in shock, as some aboard the truck tried to jump off, witnesses said. The veterans military instincts kicked in as they treated the wounded.
Residents of a town whose history and even name are inextricably linked to the railroads that run through were holding a candlelight vigil Saturday evening.
The timeline was pieced together by combining information from a video camera mounted on the front of the train, another one that was on a sheriff's car and a data recorder that acts like an airplane's black box, activating when the train blared the horn, Rosekind said.
The federal agency has also interviewed the engineer and conductor, and established the train's air brakes were working, Rosekind said. No mechanical problems were found with the cars. A review of the train's maintenance history found no defects, he added. The tracks also had no problems.
Investigators will try to establish on Monday what the engine could have seen as it approached the truck, Rosekind said.
Part of the investigation includes whether the parade had the proper permit. The parade has been an annual event in Midland for nine years, but City Manager Courtney Sharp declined to say whether the group, Show of Support/Hunt for Heroes, had the necessary paperwork to hold the event.
Railroads, though, are a vital part of Midland, a town that sits in the heart of Texas' oil rich Permian basin. Three or four tracks lie within city limits, and the site of the accident is just about 10 minutes from downtown, said Midland spokesman Ryan Stout.
That's considered when the city grants permits for parades and other events, Sharp said.
"We take all steps into consideration when we permit," he said. "I hate to go down that track until all of the investigation is over, but yes we do take that stuff into account."
The veterans were on their way to a banquet in their honor and were being cheered by a flag-waving crowd. It was supposed to be the start of a three-day weekend of banquets, deer hunting and shopping in appreciation of the veterans' sacrifice.
Killed were Marine Chief Warrant Officer 3 Gary Stouffer, 37; Army Sgt. Maj. Lawrence Boivin, 47; Army Sgt. Joshua Michael, 34; and Army Sgt. Maj. William Lubbers, 43.
Five people remained hospitalized early Saturday. In Midland, three people were in stable condition and one in critical. None of the injuries are life-threatening, said hospital spokeswoman Marcy Madrid. A fifth person who was transferred to a Lubbock hospital shortly after the accident is in serious condition.
Union Pacific spokeswoman Raquel Espinoza said the speed limit in that area was raised from 40 mph to 70 mph in 2006.