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Mark Lennihan, Associated Press
Sen. Richard Blumenthal, D-Conn., left, and Sen. Charles Schumer, D-NY, bring a bouquet of flowers to place at a railroad crossing, Friday, Feb. 6, 2015, in Valhalla, N.Y. On Tuesday a car collided with a Metro-North Railroad train at the same location, killing the car's driver and five train passengers.

VALHALLA, N.Y. — It was a hellish scenario investigators had never seen before: 400 feet of electrified third rail snapped into 40-foot pieces and speared a commuter train during a fiery collision with an SUV. Now officials want to know whether the rail's unusual design explains why the crash was so uncommonly deadly.

The pieces went through the first car of the train "like daggers going into the heart of that chamber," Sen. Richard Blumenthal, D-Conn., said Friday after touring the blackened, mangled wreckage.

The SUV driver and five passengers were killed Tuesday evening in the rush-hour collision in Valhalla, about 20 miles north of New York City. The SUV driver had stopped on the tracks, between the lowered crossing gates, for reasons still unclear to investigators.

The Metro-North Railroad is believed to be the only U.S. commuter railroad that uses the "under-running" or "under-riding" configuration: A metal "shoe" slips underneath the third rail rather than skimming along the top.

Some have questioned whether the violent collision could have caused the shoe to act as a crowbar that lifted the third rail toward the train.

"This has never happened before, and this is a rare configuration of a third rail. Do those two add up to the explanation for this terrible, terrible tragedy? Very possibly," Sen. Charles Schumer, D-N.Y., said, calling the design "a real concern."

The National Transportation Safety Board said Thursday it was looking to answer that question among many others from the crash — a rare and unusually fiery instance of passenger deaths among the thousands of train-auto collisions each year.

In other developments:

— The railroad crossing had undergone a number of upgrades in recent years to reduce the risk of accidents, but some planned work — the installation of a third set of flashing lights — was never done, for reasons officials were unable to explain.

As for whether the extra lights could have prevented the tragedy, state Transportation Department spokesman Beau Duffy said: "It's way too early to be guessing about what could have or couldn't have made a difference."

— A funeral was held for the SUV driver, 49-year-old Ellen Brody, at a synagogue in Dobbs Ferry on Friday. Brody worked at a jewelry store and was the mother of three daughters in their teens and 20s. Her rabbi, Benjy Silverman, called her a "beautiful soul" who "adored her daughters and husband. She was their biggest fan and supporter."

A railroad expert noted that the "under-running" design has been used for decades because it avoids the problems caused by ice building up on top of the third rail.

But it's impossible to say whether it was a factor in the fire without testing how the "over-running" system would have reacted in the same situation, said Steve Ditmeyer, a former Federal Railroad Administration official who teaches railway management at Michigan State University.

"One doesn't expect a train to push an automobile against the third rail," no matter how it's configured, he noted.

The third rail is a common feature of subway systems. But among the nation's 28 commuter railroads, only Metro-North and the Long Island Railroad use third rail systems at all, according to the American Public Transit Association. Others use overhead wires or other forms of power.

More than 50 miles of Metro-North have the "under-running" design. The lines were built by a private railroad about a century ago, long before Metro-North's founding in 1983.

After the train hit the SUV at the crossing in Valhalla, the third rail penetrated the SUV, then pierced the floor of the train's first car. It "kept coming in, in, in, in," breaking up into about 15 pieces and going through the car's roof as the train went 1,000 feet before coming to a stop, Schumer said.

"It's like looking into a coffin," he said of the burned-out train car. "It's one of the worst experiences I've had in elected life. ... One of the worst fires I've ever seen. It must have been a total nightmare."

The NTSB's lead investigator told the elected officials he hadn't seen anything like that happen before, Schumer said.

"Should there certainly have been something that prevents third rails in this almost freak situation from penetrating the car? Probably so," he said, cautioning that the NTSB has yet to make its findings.

NTSB vice chairman Robert Sumwalt has said the NTSB in investigating whether the third rail became de-energized, as designed, when it started to break, or was still electrified as it speared the train.

The Metropolitan Transportation Authority, which runs both Metro-North and the LIRR, declined to comment, citing the NTSB investigation.

Associated Press writers Frank Eltman in Mineola, New York; David B. Caruso in New York; and Michael Kunzelman in Baton Rouge, Louisiana, contributed to this story.