The driver of a New York train that derailed killing four people was in a dazed state known as highway hypnosis or white line fever moments before the crash, according to union officials.

Anthony Bottalico, the leader of the Association of Commuter Rail Employees, said that William Rockefeller the 43-year-old engineer in the driving compartment nodded off at the controls as the Metro-North commuter train approached a curve at a high speed and ran off the rails.

"He had the equivalent of what we all have when we drive a car," Bottalico said. "That is, you sometimes have a momentary nod or whatever that might be. How long that lasts, I can't answer."

More than 60 people were injured as the train jumped the tracks after it entered the curve at 82mph (132 km/h) - nearly three times the speed limit. One carriage smashed into the bank of the Harlem River in New York's Bronx borough.

Train data revealed that Rockefeller recovered from his numbness a few seconds before the crash and put on the brakes but too late. He suffered minor injuries in the crash.

"[Rockefeller remembers] operating the train, coming to a section where the track was still clear - then, all of a sudden, feeling something was wrong and hitting the brakes," said attorney Jeffrey Chartier. "He felt something was not right and he hit the brakes."

So-called highway hypnosis occurs when a driver goes into a semi-trance while at the wheel of a vehicle. Federal investigators have not commented on Rockefeller's level of alertness at the time of the incident.

Chartier described Rockefeller as "a guy with a stellar record".

"You've got a good guy and an accident," Chartier said. "A terrible accident is what it is."

Rockefeller had been a volunteer firefighter for 23 years and started working on the railroad 15 years ago.

Drug and alcohol tests returned negative and it appeared that he had got enough sleep before starting his nine-hour shift, said National Transportation Safety Board (NTSB) member Earl Weener.

"There's every indication that he would have had time to get full restorative sleep," Weener said.

Chartier said Rockefeller had gone to bed at 8:30 the previous night to wake up at 3:30am for his shift.

Bottalico said the driver had switched just weeks earlier from the night shift to the day shift. "So he did have a change in his hours and his circadian rhythms with regard to sleep," he said.