NORFOLK, Va. (AP) — A trash truck driver who had marijuana in his system likely caused a fatal collision last year with an Amtrak train that was carrying Republican lawmakers, federal investigators concluded Thursday.

The National Transportation Safety Board's final report said the crash in rural Virginia was likely caused by the truck driver's decision to go around a rail crossing's lowered safety gates. The agency also cited the driver's "inaction" while stopped on the tracks.

Drugs likely played a role as well, the NTSB said. The driver's blood contained the psychoactive ingredient in marijuana as well as an anti-seizure medication for which investigators found no prescription.

The ensuing collision killed a passenger in the trash truck and severely injured another. Several people on the train were hurt, including a congressman who suffered a concussion.

The train was carrying Congress members to a strategy retreat at the Greenbrier resort in White Sulphur Springs, West Virginia. The crash occurred in Crozet, just outside of Charlottesville.

The report said marijuana impairment is evident through slower decision-making and noted the driver's "indecision when he encountered obstacles while trying to cross the tracks."

"The truck driver's lack of response after stopping the truck and being positioned between two obstacles for several seconds is an example of slow decision-making," the report said.

William Tanner, Naylor's attorney during the criminal trial, did not immediately respond to a phone call from The Associated Press seeking comment.

The NTSB's findings may have little impact on the driver.

NTSB spokesman Keith Holloway wrote in an email that the agency "does not have any enforcement authority" and that "there is no legal action that can be taken by the board."

Naylor had been indicted locally on involuntary manslaughter and DUI charges.

A charge of maiming under the influence was dropped after a judge ruled out certain scientific testimony and blood evidence, the Daily Progress reported .

Last month, a jury found Naylor not guilty of involuntary manslaughter. He still faces civil suits filed by people who were on the train.