Transcripts and interviews from the National Transportation Safety Board, which is investigating the April 3 accident in Chester, PA, show miscommunication and violations of safety procedures during the changing of two shifts of track workers. That resulted in a dispatcher clearing southbound Amtrak Train 89 to proceed at more than 100 miles an hour down a track the two workers thought was closed.
Records in the NTSB docket also show that the train's engineer had trace amounts of marijuana in his blood after the crash, but there is no indication he was impaired. A medical report containing drug test results on the two workers who were killed is expected to be published later Thursday, an NTSB spokesman said.
Records in the docket don't say that the engineer was impaired when the crash occurred, but that the 47-year-old veteran engineer was in good health, and didn't suffer from sleep apnea. The engineer attempted to brake the train when he spotted the workers on the track, the records said. "He also stated that he felt alert when he went on duty," the report said.
The positive marijuana test comes amid heightened concerns from federal safety regulators about drug use among rail workers. The Federal Railroad Administration has pushed to expand mandatory drug testing at passenger and freight railroads, and warned that the relatively safe railroad sector is also susceptible to a nationwide trend of increasing drug use, including of opioids.
The federal agency expanded its mandatory drug testing program to include track workers just weeks after the Chester crash. Amtrak, in announcing the appointment of new Chief Executive Charles "Wick" Moorman, in August, specifically invoked his safety record as CEO of Norfolk Southern Corp.
And in September, Sarah Feinberg, then the administrator of the FRA, convened group meetings of both major railroads and railroad unions, urging them to confront the likelihood that the nation's opioid addiction crisis "has begun creeping into the rail industry." In November, the agency rejected an industry petition to delay the new testing requirements by one year.
The FRA's drug testing program dates to 1987, and in recent years the agency has seen an increase in positive drug test results -- both in random testing and after accidents. In 2014, FRA data showed no positive toxicology tests in post-accident testing. That rose to 2.9% in 2015, then to 4.8% in 2016.
Federal regulations prohibit certain transportation workers, including train engineers, from using controlled substances, a category that includes marijuana. In a rule adopted after the Chester crash, the FRA formally extended that class of transportation workers to include track workers, though railroad rules, including Amtrak's, already prohibited the use of most controlled substances by track workers.
The crash "obliterated" the backhoe on which the two men were working, NTSB summaries said, killing them and seriously injuring another worker. More than 40 passengers aboard the train were taken to area hospitals, the NTSB said.
The opening of the docket isn't the NTSB's final determination of the cause of the accident.
Investigators have been trying to determine if the temporary restriction on the track, known as a "foul," was improperly ordered to be removed during the handover of the work site from one crew of workers to the next, people familiar with the investigation have said.
A simple piece of safety equipment, called a supplemental shunting device or shunt, would have alerted the railroad's signal system to the presence of workers on the affected area of track, but the device wasn't in use despite Amtrak rules that required it, according to railroad and union officials.
According to records released Thursday, the night foreman who was going off duty told investigators that he asked the incoming day foreman whether he should lift the temporary restriction by phone or over the radio. The night foreman said he was told "Just go ahead and call them on the phone. Doesn't matter."
The day foreman gave a different account, telling investigators he didn't know the night foreman told the dispatcher to lift the restriction, or foul. "Last I talked to [the night foreman], he had a foul on all three tracks. I assumed everything was still fouled because I didn't hear nothing. Nobody heard anything on the radio," the day foreman said, according to the NTSB records.
Railroad industry and union officials have said that some safety measures, like the use of shunt straps, are sometimes foregone by track crews because of a variety of factors, including pressure to get on and off tracks quickly and allow trains to move more readily through areas where work is being done.
In the aftermath of the Chester crash, officials from the Brotherhood of Maintenance of Way Employes, which represents Amtrak track workers, urged members to refuse to work on job sites where shunts weren't being used according to Amtrak rules.

A botched handoff between two foremen and a train dispatcher likely doomed two Amtrak workers who were killed by a train on a stretch of track near Philadelphia last year, according to new records released Thursday.