A commuter train in the US that derailed over the weekend, killing four passengers, was hurtling at 82mph (131kph) as it entered a 30mph curve, a federal investigator says.
But whether the wreck was the result of human error or brake trouble was still unclear, he said.
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 said the information on the locomotive's speed was preliminary and extracted from the Metro-North train's two data recorders, taken from the wreckage after the Sunday morning accident in the Bronx.
He also said investigators had begun interviewing the crew members, but he would not disclose what the engineer had told them.
Weener said the throttle went to idle six seconds before the derailed train came to a complete stop - "very late in the game" for a train going that fast" - and the brakes were fully engaged five seconds before the train stopped.
He said investigators were also examining the engineer's mobile phone - apparently to determine whether he was operating the train while distracted.
Asked whether the tragedy was the result of human error or faulty brakes, Weener said: "The answer is, at this point in time, we can't tell."
As investigators mined the data recorders for information, workers righted the fallen cars along the curve, a bend so sharp that the speed limit during the approach drops from 70mph to 30mph.
The wreck came two years before the federal government's deadline for Metro-North and other railways to install automatic-slowdown technology designed to prevent catastrophic accidents. But with the cause of Sunday's wreck unknown, it was not clear whether the technology would have made a difference.
The engineer, William Rockefeller, was injured and "is totally traumatised by everything that has happened," said Anthony Bottalico, executive director of the rail employees union. He said Rockefeller, 46, was cooperating fully with investigators.
The NTSB has been urging railways for decades to install technology that can stop wrecks caused by excessive speed or other problems. Congress in 2008 required dozens of railways, including Metro-North, to install the "positive train control" systems by 2015.
But the systems are expensive and complicated and cannot prevent an accident if there is a brake failure. Railways are trying to push back the deadline a few years.
