NEW YORK — Two data recorders retrieved from the commuter train that derailed while rounding a riverside curve, killing four people, may provide information on the speed of the train, how the brakes were applied and the throttle setting, a member of the National Transportation Safety Board said Monday.

The NTSB was downloading data from a recorder previously found in the rear locomotive in the 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.

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

Investigators plan to conduct interviews Monday or Tuesday with the engineer and conductor, Weener said. He also said clues could be found from a signaling system operated by dispatchers at a central location.

Workers began the arduous task of righting the toppled rail cars. Five passenger cars and the locomotive were back on the tracks by around 9:30 a.m.

Officials warned the 26,000 weekday riders on the affected line of the nation’s second-biggest commuter railroad to brace for crowded trains; shuttle buses were being provided. However, Metro-North Railroad spokesman Aaron Donovan said no major delays were reported during the early part of the rush hour.

“We’d like to get service up toward the end of the week,” Gov. Andrew Cuomo said.

About 150 people were on board when the train derailed Sunday morning on Metro-North’s Hudson line. About 60 were injured. Mayor Michael Bloomberg said 11 patients initially in critical condition did not appear to have life-threatening injuries.

The NTSB said its investigators could spend up to 10 days probing all aspects of the accident that toppled seven cars and the locomotive at a bend in the Bronx where the Hudson and Harlem rivers meet. 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.

Cuomo said on NBC’s “Today” show that he thinks speed will turn out to be a factor. The governor, speaking from the crash site for a second day, 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.”

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.

As deadly as the derailment was, the toll could have been far greater had it happened on a weekday, or had the lead car plunged into the water instead of nearing it. The train was about half-full at the time of the crash, rail officials said.

Joel Zaritsky, who was dozing as he traveled to a dental convention, awoke to feel his car overturning several times.

“Then I saw the gravel coming at me, and I heard people screaming,” he said, holding his bloody right hand. “There was smoke everywhere and debris. People were thrown to the other side of the train.”

One passenger, Frank Tatulli, told WABC-TV that the train appeared to be going “a lot faster” than usual as it approached the sharp curve near the Spuyten Duyvil station.

Nearby residents awoke to a building-shaking boom. Angel Gonzalez was in bed in his high-rise apartment overlooking the rail curve when he heard the roar.

“I thought it was a plane that crashed,” he said.

Within minutes, dozens of emergency crews arrived and carried passengers away on stretchers, some wearing neck braces. Others, bloodied and scratched, held ice packs to their heads. In their efforts to find passengers, rescuers shattered windows, searched nearby woods and waters and used pneumatic jacks and air bags to peer under wreckage.

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 Monday.

Lovell, an audio technician, was traveling to midtown 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 staff.

Though the cause of the crash 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. 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.

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.