NEW YORK » Two data recorders retrieved from the commuter train that veered off a sharply curved track by a river’s edge, killing four people, may shed light on key factors including the train’s speed and how brakes were applied, a National Transportation Safety Board member said today as the agency sought to ask the engineer and conductor what went wrong.

The NTSB was downloading data from a recorder previously found in the rear locomotive in the Metro-North Railroad train that derailed Sunday in New York. A second recorder was found in the front car of the train and has been sent to Washington for analysis, NTSB board member Earl Weener said.

Investigators have already had some success in retrieving data, but the information has to be validated before it’s made public, Weener said.

Investigators planned to interview the engineer and conductor today or Tuesday, Weener said. He said clues also could be found from a signaling system, which dispatchers operate from a central location.

Workers began righting the toppled rail cars today as the 26,000 weekday riders of the affected line used shuttle buses and cars to get to work. But no major delays were reported during the early rush hour, railroad spokesman Aaron Donovan said.

Marketing worker Leanne Bloom, 40, normally takes the affected Hudson Line to work but drove to a stop on another line instead. She was surprised to find the train nearly empty.

"I was expecting long lines" at the station, she said. "But I made it very easily."

About 150 people were on board when the train ran off the rails around 7:20 a.m. Sunday while rounding a bend where the Harlem and Hudson rivers meet in the Bronx, leaving four dead and injuring more than 60 including the engineer. He was identified as William Rockefeller, according to two officials familiar with investigation who spoke to The Associated Press on condition of anonymity because they weren’t authorized to speak publicly.

An engineer for about 11 years and a Metro-North employee for about 20, Rockefeller "is totally traumatized by everything that has happened," said Anthony Bottalico, executive director of the Association of Commuter Rail Employees, the union representing all the crew members. He said Rockefeller, 46, was "cooperating fully to get to root cause" of the wreck.

"He’s a sincere human being with an impeccable record, that I know of. He’s diligent and competent," Bottalico said.

The train’s assistant conductor, Maria Herbert, suffered an eye injury and a broken collarbone in the crash, Bottalico said.

While many survivors had been discharged from hospitals by this afternoon, seven were still in an intensive-care unit at St. Barnabas Hospital, some with spinal injuries, according to Dr. David Listman, the emergency department director.

Two patients out of seven remained in critical condition at NewYork-Presbyterian Hospital, hospital officials said.

Overall, the injured ranged from five police officers who were heading to work, according to Mayor Michael Bloomberg, to a 14-year-old boy who was taking a weekend ride with his father on the same train the boy usually takes to school.

The boy had been released. But in the wake of the accident, the boy’s mother wondered, "How is he going to get back on a Metro-North train to go back to school?" said Listman, recalling his conversation with her.

The NTSB said its investigators could spend up to 10 days at the crash scene to probe all aspects of the accident, which happened with the train about half-full. The speed limit on the curve is 30 mph, compared with 70 mph in the area approaching it, Weener said.

The agency said it would consider whether excessive speed, mechanical problems or human error played a role in the crash.

Though the cause is not yet known, the NTSB has been urging railroads for decades to install technology that can stop derailing caused by excessive speed, along with other problems.

A rail-safety law passed by Congress in 2008 gave commuter and freight railroads until the end of 2015 to install the systems, known as positive train control. PTC is aimed at preventing human error — the cause of about 40 percent of train accidents. But the systems are expensive and complicated and can’t prevent an accident if there’s a brake failure. Railroads are trying to push back the installation deadline another five to seven years.

Metro-North is in the process of installing the technology. It now has what’s called an "automatic train control" signal system, which automatically applies the brakes if an engineer fails to respond to an alert that indicates excessive speed.

Such systems can slow trains in some circumstances but not bring them to a halt, said Grady Cothen, a former Federal Railroad Administration safety official.

Cuomo said on NBC’s "Today" show that he thinks speed will turn out to be a factor. The governor said other possible factors ranged from equipment failure and operator failure to a track problem.

"It was actually much worse than it looked," Cuomo said.

"As the cars were skidding across the ground, they were actually picking up a lot of debris, a lot of dirt and stones and tree limbs were going through the cars so it actually looked worse up close," he said, calling it "your worst nightmare."

The Metropolitan Transportation Authority, which runs Metro-North, identified the victims as Donna L. Smith, 54, of Newburgh; James G. Lovell, 58, of Cold Spring; James M. Ferrari, 59, of Montrose; and Ahn Kisook, 35, of Queens. Three of the dead were found outside the train; one was inside. Autopsies were scheduled for today.

Lovell, an audio technician, was traveling to Manhattan to work on the famed Rockefeller Center Christmas tree, longtime friend Janet Barton said. The tree-lighting ceremony is Wednesday night.

The "Today" show expressed condolences to the family of Lovell, a married father of four who had worked on the program and other NBC shows. "He always had a smile on his face and was quick to share a friendly greeting," ”Today" executive producer Don Nash said in a message to staffers.

It was the latest mishap in a troubled year for Metro-North, which had never before experienced a passenger death during an accident in its 31-year history.

Sunday’s accident came six months after an eastbound train derailed in Bridgeport, Conn., and was struck by a westbound train. The crash injured 73 passengers, two engineers and a conductor. In July, a freight train full of garbage derailed on the same Metro-North line near the site of Sunday’s wreckage.

Associated Press writers Kiley Armstrong, Verena Dobnik, Deepti Hajela, Ula Ilnytzky, Colleen Long, Jake Pearson and Jennifer Peltz in New York, Joan Lowy in Washington and Stephen Singer in Hartford, Conn., contributed to this report.