An engineer whose speeding commuter train ran off the rails along a curve, killing four people, experienced a hypnoticlike daze and nodded at the controls before he suddenly realized something was wrong and hit the brakes, a lawyer said as a federal regulator called for the railroad to make immediate safety improvements.

William Rockefeller, who was operating the Metro-North Railroad train, experienced a nod or “a daze,” almost like road fatigue or the phenomenon sometimes called highway hypnosis, said attorney Jeffrey Chartier, who accompanied the engineer to his interview with National Transportation Safety Board investigators Tuesday. Chartier couldn’t say how long the spell lasted.

What Rockefeller remembers is “operating the train, coming to a section where the track was still clear — then, all of a sudden, feeling something was wrong,” Chartier said. “He felt something was not right, and he hit the brakes.”

He called Rockefeller “a guy with a stellar record who, I believe, did nothing wrong.”

“You’ve got a good guy and an accident,” he said. “A terrible accident is what it is.”

Rockefeller “basically nodded,” said Anthony Bottalico, leader of the rail employees union, relating what he said the engineer told him.

“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.”

It’s too soon to say whether the accident was caused by human error, NTSB member Earl Weener said. But investigators have found no problems with the brakes or rail signals, he said. Alcohol tests on crew members were negative, and investigators are awaiting the results of drug tests, the NTSB said.

Federal investigators wouldn’t comment on Rockefeller’s level of alertness. They said late Tuesday they had removed Bottalico’s union, the Association of Commuter Rail Employees, as a participant in the investigation for publicly discussing confidential information.

Joseph Szabo, head of the Federal Railroad Administration, said in a letter Tuesday that his administration and the U.S. Transportation Department “have serious concerns” after Sunday’s accident and three others that occurred in New York and Connecticut from May through July.

Though a federal team has been working closely with Metro-North Railroad and its parent agency, the Metropolitan Transportation Authority, Szabo said, “immediate corrective action is imperative.”

The MTA said in a statement that it would work with federal agencies to improve safety, and was “conducting a comprehensive probe of the safety culture throughout the MTA.” Railroad employees were also getting expanded safety briefings.

Congress had previously ordered commuter and freight railroads to install technology called positive train control, which uses electronics to monitor trains’ positions and speed and stop derailments and other problems, by the end of 2015. The technology has not been installed on Metro-North trains.

The MTA has said it started planning for such a system as soon as the law went into effect, but it has advocated for an extension to 2018 because of difficulties in installing it.

Crews are rebuilding the damaged track where Rockefeller’s train crashed. One of three Hudson Line tracks reopened Wednesday, and commuters said they were grateful service was restored fairly quickly.

“We don’t get to complain,” said Elite Rubin, 36, who does marketing for an accounting firm. “We weren’t on that train where people died.”