NEW YORK (CBSNewYork/AP) — The National Transportation Safety Board will release its final report on the deadly February 2015 crash between a Metro-North commuter train and an SUV at a crossing in Valhalla.

A U.S. official told The Associated Press that investigators determined the crash was extra deadly because of an unusual rail design.

NTSB investigators found that about 340 feet of electrified rail was pulled up from the ground, penetrated the SUV’s fuel tank and then sliced into the train, according to the official, who was not authorized to discuss an ongoing investigation and spoke to the AP on the condition of anonymity.

The rail was an under-running or under-riding design, in which a metal shoe slips underneath the electrified third rail, rather than skimming along the top. Questions were raised after the crash about whether the collision caused the shoe to pry up the third rail. Metro-North, which operates in New York and Connecticut, is believed to be the only U.S. commuter railroad with the under-riding rail configuration.

Gallery: NTSB Releases Valhalla Metro-North Crash Photos

NTSB investigators also are recommending risk assessments be conducted for grade crossings, the official said.

The Metropolitan Transportation Authority, which operates Metro-North, “will carefully review any safety recommendations” made by NTSB investigators, MTA spokesman Aaron Donovan said.

Six people were killed and more than a dozen others injured when the train crashed into the SUV on the tracks at a crossing in Valhalla. The impact sparked an explosion, and flames blasted into the passenger area, burning out the first car of the train.

Passengers were trapped in the fiery, mangled wreckage and tried to pry open the doors to escape. One passenger, whose hands, shirt and hair were on fire, shattered an emergency box and then pried the doors open before leading a group of passengers out of the wreckage.

More: Deadliest Train Crashes Near NYC, Tri-State Area

The SUV’s driver, Ellen Brody, had stopped in traffic on the tracks, between the lowered crossing gates. Witnesses said Brody got out of her SUV to inspect the damage to it before driving forward and being struck by the oncoming train.

Federal safety investigators say they haven’t been able to determine why Brody drove her car into the crossing. Investigators found that warning gates and lights worked properly.

NTSB head Robert Sumwalt hypothesized that Brody had been in traffic and wasn’t aware she was in a rail crossing.

Brody’s husband is suing Metro-North, the MTA and the train’s engineer, saying the crash was caused by a badly designed grade crossing and improper warning signs. Alan Brody says his wife must not have realized she was on a railroad track.

After hearing from the AP about the NTSB’s findings, he noted Monday that courts also are being asked to weigh the crash and its causes. He said he’ll continue pressing the MTA to modernize and improve the railroad.

“There are substantial systemic issues at stake here, and, you know, somebody has to take it on,” he said. “I’m dead serious about it. I have a reason to be dead serious about it. They (officials) didn’t lose anyone.”

A data recorder showed the train’s engineer hit the emergency brakes and sounded the horn as the train bore down on the Valhalla crossing, traveling 58 mph in a 60 mph zone, the NTSB has said.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)