PHILADELPHIA (AP) — A federal investigation into what caused a speeding Amtrak train to slam into a backhoe last year near Philadelphia, killing two maintenance workers, already has found evidence of a lax safety culture, poor communication and employee drug use at the government-owned railroad.

Now, with the investigation wrapping up, the National Transportation Safety Board is meeting Tuesday to review the findings and determine a probable cause of the April 3, 2016 crash in Chester, Pennsylvania.

Backhoe operator Joseph Carter Jr. and supervisor Peter Adamovich were killed and 40 passengers on the New York to Savannah, Georgia, train were injured.

The NTSB’s investigation found that the maintenance crew failed to follow safety procedures designed to keep workers safe and that Amtrak management was wrong to let the work go on without a detailed plan identifying hazards and ways to mitigate them.

Amtrak contended that the work was part of an ongoing, routine maintenance project that did not require a detailed plan. Investigators, in a sharp rebuke that was not meant to be made public, said the railroad’s explanations “are simply a post-accident circling of the wagons to deny supervisory or management involvement in the review of a project gone bad.”

Toxicology reports showed that Carter, 61, had cocaine in his system and Adamovich, 59, tested positive for morphine, codeine and oxycodone. The train’s engineer, 47-year-old Alexander Hunter tested positive for marijuana, according to the reports.

Hunter is no longer employed by Amtrak. No amount of marijuana use by an engineer is acceptable, the railroad said.

The unions representing maintenance workers and train engineers suggested the probable cause of the crash was the crew’s failure to use a device that blocks access to tracks where maintenance crews are working. The unions also cited the crew’s failure to ensure that all workers and maintenance equipment were clear of the tracks.

The Brotherhood of Maintenance of Way Employes said in a filing with the NTSB that drugs played no role in the severity or cause of the crash. The union described “an absence of a just and mature safety culture at Amtrak” and a lack of “communication, collaboration, cooperation, and trust” between labor and railroad management.

In its filing, Amtrak blamed the foremen running the maintenance operation for failing to comply with the railroad’s rules, policies and procedures. Amtrak said it has since issued safety alerts and advisories reminding workers of safety rules and that it is improving worker protection training programs.

Hunter told investigators that he knew of maintenance work being done in the area but was not given any warnings about equipment being on the same track as his train.

Hunter blew the train’s horn and hit the brakes once he saw equipment on an adjacent track and then on his own track, about five seconds before impact.

The train slowed from 106 mph to 100 mph at impact and only came to a complete stop about a mile down the track. The lead engine of the train was derailed.

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