The train carrying members of Congress to a Republican retreat in West Virginia last month struck a garbage truck that had entered a railroad crossing after safety gates had come down, according to a new report released Wednesday.

The National Transportation Safety Board said in a preliminary report that witnesses told investigators the truck drove onto the crossing after the warning gates had lowered.

The train, which was operated by Amtrak, also had a forward-facing camera, which showed as the crossing came into view, "the gates were down and the refuse truck was on the grade crossing."

One trash company employee was killed in the Jan. 31 crash, while the truck driver, another employee and several others on the train were injured.

The NTSB said the crash happened around 11:16 a.m., as the Congressional Special Amtrak Train 923 approached the crossing in Crozet, Va. at about 61 miles per hour when "the engineer applied emergency braking."

After striking the truck, an axle on the front locomotive on the train derailed but remained upright, according to the NTSB.

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Several people who live near the railroad crossing told The Associated Press that the safety gates, which are designed to come down to warn drivers of approaching trains, were known to frequently malfunction, sometimes staying down for extended periods of time even when no trains were coming.

"The track and operational characteristics of the crossing signals were also examined and documented," the NTSB said in its report. "NTSB investigators continue to examine issues related to the highway–railroad grade crossing."

The agency said the probable cause of the accident hasn't yet been determined.

Congressional members were on the chartered train to the Greenbrier resort, where the party traditionally gathers to discuss its agenda and goals for the coming year.

"It was a very high-speed collision," Rep. Jeff Denham, R-Calif., who was on board, told Fox News at the time. "There was no braking that was felt. We hit an immediate impact and went from 70 to zero very quickly."

The train -- which had a functional engine on the other end -- was able to run in reverse back to Charlottesville, where members took buses to West Virginia.

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The crash was the latest tragedy to affect congressional Republicans, who were targeted in a shooting last summer at a baseball practice in northern Virginia. The lawmaker most seriously injured in that attack, U.S. Rep. Steve Scalise, R-La., was not on the train during the crash.

Fox News' Judson Berger, Chad Pergram, and the Associated Press contributed to this report.