On a 5-0 vote, the panel also agreed that the weakness of passenger car walls likely contributed to the number of deaths and more than a dozen injuries after the truck skidded 300 feet into the train at a rural crossing on June 24, 2011. It recommended new strength standards be developed.
NTSB investigators said the truck driver apparently didn't notice the train because he was fatigued as a result of inconsistent sleeping patterns, was suffering from ankle pain or possibly could have been checking messages on his cellphone. But the panel decided there wasn't enough evidence of any of those things to include in the formal probable cause finding issued during a hearing in Washington.
Board members also ruled out the possibility the crossing guard gate or warning lights malfunctioned after time-lapsed photography showed the gate fully extended four seconds before the crash. Monitoring equipment also indicated the warning lights were flashing and the gate in place 18 seconds before the collision when the truck was still 900 feet away from the crossing.
The truck driver, Larry Valli, 43, was killed along with the train's conductor and four passengers.
NTSB chairwoman Deborah Hersman said Valli had plenty of opportunity to see and react to the lights.
"This accident could have easily been prevented if the driver had acted appropriately or the motor carrier had acted responsibly in maintaining the vehicle," she said.
Officials for the owner of the truck, John Davis Trucking Co. of Battle Mountain, and their lawyer did not immediately respond to messages from The Associated Press seeking comment.
Investigators said they weren't able to find any immediate relatives of Valli.
The California Zephyr bound from Chicago to Emmeryville, Calif., was three hours behind schedule when it left Salt Lake City on the day of the crash.
It was going 77 mph in northern Nevada's Forty Mile Desert and approaching the crossing at U.S. Highway 95 north of Fallon when the engineer noticed that a semi-truck hauling two open empty trailers didn't seem to be slowing for the oncoming train, according to the NTSB's preliminary findings.
With the whistle blaring, the engineer initiated the emergency brakes about 450 feet from the crossing. Rubber skid marks on the highway show the truck driver hit his brakes 300 feet from the tracks but skidded nearly the length of a football field into the side of the train, investigators said. If the brakes had been properly maintained, the truck should have stopped within about 230 feet of braking, they said.
Valli, of Winnemucca, had been talking on a cellphone earlier in the day, the NTSB said. He was not talking on the phone at the time of the crash, but he did receive a call a few minutes before that and, while he didn't answer it, it's possible he could have subsequently been checking his voice mail, investigators said.
Board member Robert Sumwalt said he found it "phenomenal" that the driver didn't react to the crossing warning sooner.
"I cannot imagine barreling down the highway at 60 mph and wait until you are less than the length of a football field before applying the brakes," he said. "This accident could have been avoided if the driver would have applied brakes 1.4 seconds sooner or if John Davis Trucking would have maintained the brakes as they should have been maintained."
The truck embedded in the side of a crew car, which ultimately was destroyed by the fire that also charred a passenger car behind it.
The children of the conductor, Laurette Lee, 68, of South Lake Tahoe, Calif., are among those who have sued over the crash, naming Valli and John Davis Trucking as defendants.
NTSB investigator Jennifer Morrison said 11 of the truck's 16 brake drums were worn beyond limits. She said tests conducted by the Nevada Highway Patrol also found nine of the 16 brakes were out of adjustment or inoperative, but she said the patrol didn't use the proper test guidelines so it was not possible to tell for sure if those results were entirely accurate.
Those conditions might not have been obvious to the driver, who likely would not have known his brakes were faulty unless he'd been required to make a quick stop before, she said.
However, NTSB also discovered the warning lights and anti-lock brake system had been deliberately disconnected and the wiring gathered in a loop for an unknown reason.
The NTSB found Valli had been cited for 11 speeding violations over the past 10 years but less than half were known to John Davis because the firm only checked his Nevada background. The probe also determined Valli had 30 different employers over the past 10 years but didn't include at least two that had terminated him on his John Davis application.
As a result, the board recommended Tuesday that commercial motor carriers be required to conduct and document investigations into driver histories for the 10 years prior to their application for employment.
Among other things, the panel also recommended the development of side-impact worthiness standards to minimum encroachment into rail cars and requiring passenger rail car doors to be designed to prevent fire and smoke from moving between cars -- although they acknowledged fire doors would not have made a difference in this case.
The passengers killed in the accident were: Cheuy Ong, 34, of West Jordan, Utah; Francis Knox, 58, and Karly "Annie" Knox, 18, of Seward, Neb.; and Barbara Bell, 60, of United Kingdom.
Senate Majority Leader Harry Reid commended the investigative team for providing "insight into the causes of the tragic collision."
"Today, as we reflect on the accident, my thoughts go out to the family and friends of those individuals who lost their lives in the collision and to those who were injured," he said in a statement. "The recommendations set forth today by NTSB will go to improve transportation safety and I look forward to receiving a full briefing on the investigation's findings in the near future."
Associated Press reporter Ken Ritter contributed to this report from Las Vegas.
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