CSX Corp.’s lax approach to safety caused a fatal collision between a passenger train and one of the company’s parked freight trains last year, U.S. accident investigators concluded Tuesday.

The National Transportation Safety Board cited what it called multiple layers of failure at CSX (CSX.O) that led a conductor to leave a switch in the wrong position, sending an Amtrak train onto a side track. The NTSB also cited U.S. railroad regulators for repeated failures to adopt safety requirements.

“Invariably humans will commit errors,” NTSB Chairman Robert Sumwalt said at the hearing. “We have to have enough redundancy in the system so that when that error is committed that error will be trapped before bad things happen -- and CSX failed to do that.”

The collision killed the Amtrak engineer and conductor at 2:27 a.m. on Feb. 4, 2018, in Cayce, South Carolina. Another 74 people were injured, nine of them seriously.

The southbound Amtrak train was operating in a zone of CSX-owned track on which warning switches had been deactivated so the railroad could install a new automated safety system known as Positive Train Control. A CSX conductor had left a switch in a position that sent the Amtrak car onto a side track where the other train was parked, NTSB found.

There were multiple underlying reasons for the accident, investigators found. A form required by CSX to remind workers they’d properly set switches hadn’t been filled out. Mandatory training hadn’t been performed. CSX didn’t follow some of the same protections as other railroads during those conditions.

The Federal Railroad Administration hadn’t followed earlier recommendations by the NTSB to impose more stringent safety practices when warning signals are disabled, the NTSB concluded. The NTSB voted to classify FRA’s response to its earlier requests as “unacceptable.”

The FRA had “diligently followed up on” NTSB’s recommendation by issuing an advisory urging railroads to take additional precautions during track repairs, such as reducing train speeds, the agency said in a statement.

CSX didn’t respond to requests to comment on the NTSB findings.

The NTSB, which issued a series of recommendations, has no authority to impose fines or enact new regulations.