A notice of claim against the Metropolitan Transportation Authority, the first step in a lawsuit, was filed on behalf of Denise Williams, a retired Army colonel and dentist who was aboard the train, attorney Michael Lamonsoff said.
He did not specify damages, but said the railroad will be accused of negligence, adding state law requires a negligence claim to be directed at the railroad and not the train engineer.
The driver was "nodding off" and braked too late to prevent the derailment, a union representative told CNN Tuesday.
"I think most people are leaning towards human error," Anthony Bottalico, acting director of the Association of Commuter Rail Employees, told the network, adding engineer William Rockefeller Jr. acknowledges his responsibility in the deadly Sunday morning accident that also injured 67 people.
Law enforcement sources told CNN Rockefeller said he was "in a daze" moments before the crash. Rockefeller's alcohol breath tests were negative, though other toxicology tests were still outstanding.
Rockefeller earlier told investigators he braked before the curve but the train kept going. Examiners said the brakes worked fine at nine earlier stops.
Rockefeller, 45, told supervisors he hit the brakes before the Metro-North Commuter Railroad train reached one of the sharpest curves in the region's rail system but it would not stop, sources told the New York Daily News.
The National Transportation Safety Board said the train was traveling 82 mph in a 70 mph area just before it hurtled off the rails at the turn, where the speed limit is 30 mph.
The braking came "very late in the game," NTSB member Earl Weener told reporters.
The train's engine still had power and the brakes weren't fully engaged even when the seven-car train tumbled off the tracks and careened toward the Harlem River, north of Spuyten Duyvil station in the Bronx, Weener said.
The throttle wasn't "reduced to idle" until 6 seconds before the locomotive, at the rear of the train, finally ground to a stop, he said. The brakes weren't fully applied until 5 seconds before the locomotive stopped.
It remained unclear if the speed was a result of human error or faulty equipment, Weener said.
Authorities said the train's brakes appeared to have been working fine shortly before the crash.
"We are not aware of any problems or anomalies with the brakes," Weener said.
"The train did make nine stops before coming to this curve," said Sen. Chuck Schumer, D-N.Y., citing the NTSB. "So clearly the brakes were working a short time before."
The safety board said the tracks in the area also seemed in proper condition, Schumer said.
When asked if the safety board was probing the possibility Rockefeller fell asleep, was using his cellphone or was otherwise distracted, NTSB spokesman Keith Holloway told The New York Times, "Part of our investigation, as in all investigations, is to look at human performance factors."
Rockefeller's cellphone was recovered as "part of our routine process," Weener said.
Investigators don't think he was on it at the time of the crash, CNN reported.
Rockefeller, who was among those injured in the wreck, was treated at a hospital and released.
The safety board's interview with Rockefeller, who lives in Germantown, N.Y., about 115 miles north of New York City, was cut short Monday afternoon because of "the trauma of the whole thing and the lack of sleep" for Rockefeller, Bottalico told the Times.
The interview is to resume this week, officials said.
New York City and Metropolitan Transportation Authority police, along with Bronx District Attorney Robert Johnson, were mounting a separate investigation into the accident, the Times said.