Portland, Oregon (CNN) In the days before Amtrak 501 careened off the tracks last month in a deadly crash, engineers and conductors warned their supervisors that they did not feel adequately trained on the new route, according to more than a dozen sources.

Several train cars flew off an overpass, landing on Interstate 5 in the December 18 accident near DuPont, Washington, which left three dead and more than 100 injured. At the time, Amtrak 501 was making its inaugural journey of a new Seattle-to-Portland run called the Point Defiance Bypass route.

Engineers and conductors had safety concerns, citing rushed and "totally inadequate" training which left them feeling dangerously unprepared for the new route, according to multiple sources, including several directly involved in the training. Crew members traditionally train on new routes to familiarize themselves with the signs, terrain and other physical characteristics which vary from route to route.

Some training runs were performed at night, with as many as six or more crew members stuffed into cars with just three seats, which meant some trainees rode backwards, in the dark, the sources said. Engineers felt they did not get enough practice runs at the controls and could not properly see to familiarize themselves with the route.

Adding to the training concerns, the new locomotives for the maiden run were unfamiliar to many of the crew members up until the brief training runs, the sources said.

The engineer for Amtrak 501 told investigators he took seven to 10 observational training trips on the new route, but was only at the controls for three one-way trips, and only one of those was in the direction the train was traveling when it crashed, according to an interim report released this week by the National Transportation Safety Board.

The engineer did not respond to CNN's requests for comment, but according to the report he told the NTSB "he would not have gotten behind the throttle if he had any reservations about his readiness to operate the train."

Amtrak 501 was travelling at near 80 miles an hour while heading into a turn with a maximum speed of just 30 mph. The engineer told the NTSB he missed at least two signs which would have warned him to slow down, then "as soon as he saw the 30 mph sign at the start of the curve, he applied brakes. Seconds later, the train derailed as it entered the curve," according to the NTSB report.

When asked about allegations of inadequate training, Amtrak referred CNN to the NTSB, which said in a statement, "NTSB investigators are aware of the issues that have been raised regarding training of the Amtrak 501 crewmembers."

Amtrak also said in a statement to CNN, "Our highest priority is ensuring the safety of our passengers, our crew and the communities we serve. We are actively taking measures to strengthen the safety of our operations, from adopting a safety management system approach used by commercial aviation to advancing Positive Train Control across the network. We will continue to work with the NTSB to learn from this accident and improve."

Amtrak employees who spoke to CNN insisted on remaining anonymous out of fear of losing their jobs.

More than a half dozen lawsuits have been filed so far in the crash, all alleging that inadequate crew training contributed to the accident. One of the lawsuits was filed by a conductor who was training in the lead locomotive when Amtrak 501 crashed.

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His attorney, Anthony Petru, told CNN that warnings to managers about the lack of training went unheeded.

"In an environment where there is a quick trigger by management to charge employees with insubordination, or to go after them if they report safety concerns, there was some hesitancy by employees to do anything other than go along with the program," Petru said.

Train accident investigator John Hiatt says it is clear to him the engineer had lost track of his location on the route, and blames the problems with training and preparation, at least in part, for the crash. Hiatt is an investigator with the Bremseth Law Firm of Minnetonka, Minnesota, which has filed a lawsuit on behalf of another Amtrak employee.

​"Training is money, and in this case it looks to me like they were worried about money and time and safety was number three, at best, on their list," Hiatt said.

The Point Defiance Bypass was the final piece of an $800 million project under a federal economic stimulus for high-speed rail.

But the federal money was due to run out, and the pressure to get the maiden voyage done and open the line resulted in sped-up training, sources told CNN.

The crash of Train 501 is again raising larger concerns about what many call a failing safety culture at Amtrak.

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In 2016, Amtrak train 89 crashed near Chester, Pennsylvania, killing two and injuring 35.

After a year-and-a-half-long investigation the NTSB released its findings on the Pennsylvania crash, stating that the wreck there showed "deficient safety management across many levels of Amtrak."

NTSB chairman Robert Sumwalt concluded: "Amtrak's safety culture is failing, and is primed to fail again, until and unless Amtrak changes the way it practices safety management." He added, "investigators found a labor-management relationship so adversarial that safety programs became contentious at the bargaining table, with the unions ultimately refusing to participate."

That NTSB warning and report were released on November 14, 2017. Little more than a month later, December 18, Amtrak 501 crashed.

In addition to questions about the training, questions have been raised about why the new line did not have Positive Train Control, or PTC. This could have remotely slowed the speed of Amtrak 501 and was due to be operational on the Point Defiance Bypass line later this year. The decision was made to open the line before PTC was installed.

The Rail Safety Improvement Act of 2008 called for PTC to be implemented nationally for passenger railroads and some freight railroads by December 2015, which has since been extended to the end of 2018. The deadline could be pushed further back to December 31, 2020, according to Department of Transportation.

Only 24% of passenger railway routes had PTC actively operating as of the end of 2016.

According to Washington state DOT, the Amtrak Cascades route will now not run on Point Defiance Bypass until PTC is activated.