YONKERS, N.Y.

- A commuter train that derailed over the weekend, killing four passengers, was hurtling at 82 mph as it entered a 30-mph curve, a federal investigator said yesterday. But whether the wreck was the result of human error or mechanical trouble was unclear, he said.

Rail experts said the tragedy might have been prevented if Metro-North Railroad had installed automated crash-avoidance technology that safety authorities have been urging for decades.

The locomotive's speed was extracted from the train's two data recorders after the Sunday-morning accident, which happened in the Bronx along a bend so sharp that the speed limit drops from 70 mph to 30 mph.

Asked why the train was going so fast, National Transportation Safety Board member Earl Weener said: "That's the question we need to answer."

Weener would not disclose what the engineer operating the train told investigators, and he said results of drug and alcohol tests weren't yet available. Investigators are also examining the engineer's cellphone, apparently to determine whether he was distracted.

Engineers may not use cellphones while on the train, according to the Metropolitan Transportation Authority, which runs Metro-North.

The engineer, William Rockefeller, was injured and "is totally traumatized by everything that has happened," said Anthony Bottalico, executive director of the rail employees union.