Crew fatigue brought on by irregular work schedules and a moderate form of sleep apnea is the primary reason behind a middle-of-the-night train crash that killed two Union Pacific workers and injured two others in northern Arkansas, the National Transportation Safety Board said Tuesday.
The panel also blamed an automatic horn that improperly reset alarms and the railroad industry's slow adoption of a system to stop trains automatically.
The conductor and engineer killed in the crash were likely sleeping in their southbound train as it sped through a stop signal Aug. 17, 2014, and hit a northbound Union Pacific train, the board found.
"This tragedy illustrates what can happen when identified weaknesses in safety protection are not addressed," NTSB Chairman Christopher Hart said to open Tuesday's hearing. "The crew of the train did not stop or slow their train in response to three restrictive signals. This action is indicative of fatigue, a problem that occurs so regularly it is on the most-wanted list of transportation safety improvements."
A railroad spokesman declined comment ahead of the hearing and did not return telephone calls for comment placed after the board's vote.
Investigators found that, as the train approached Hoxie, a town of 2,700 near the Missouri border, the southbound crew activated an automatic horn that repeats blasts in a long-long-short-long sequence until being shut off. As each cycle started anew, it reset a device designed to ensure the crew is alert. Had it worked properly, the engineer and conductor would have been warned at least three times that something wasn't right. If they didn't respond to the warnings, the train would have applied its brakes automatically.
The investigators also found that either the conductor or the engineer disengaged the horn 44 seconds before the crash, but the board's medical officer said it was likely just as a reflex. "Have you ever hit the alarm, the snooze button on your alarm clock?" Dr. Mary Pat McKay told the board. "Automated responses can happen when you are not awake. We can explain the turning off of the horn."
The conductor had worked an irregular schedule ahead of his final trip while the engineer had moderate sleep apnea that he was not required to report. Union Pacific required that only severe cases be disclosed.
After its 3-1 vote on the cause of the 2014 accident, the board unanimously recommended that railroads and government agencies screen for sleep apnea among transportation workers, citing its increasing role in accidents.
The condition has been implicated in a September crash in northern New Jersey that killed one person and a 2013 crash in the Bronx on the Metro-North Railroad Hudson Line that killed four. Crew fatigue was a factor in fatal train collisions in Red Oak, Iowa, in 2011, and Newton, Massachusetts, in 2008.
The board also renewed its call for "positive train control," which uses GPS-based technology to monitor and control train movement.
NTSB vice chairman T. Bella Dinh-Zarr voted against the findings. She said that since the board has been advocating for a form of positive train control since 1970, it deserved greater attention so "there aren't catastrophic results because of one simple human mistake."
Most railroads face a December 2018 deadline to install the technology.