The Governor of New York, Andrew Cuomo, has told CNN that the site where the North-West train derailed was "a dangerous area on the track just by design".
The trains are going about 70 miles per hour coming down the straight part of the track. They slow to about 30 miles per hour to make that sharp curve ... where the Hudson River meets the Harlem River and that is a difficult area of the track.
Passengers on the North-West train which derailed in New York, killing at least four, have told how they thought they were travelling "a lot faster" than usual prior to its crash.
"It was coming towards Spuyten Duyvil and you could feel it starting to lean and it was like 'hey what's going on, and then it hit the curb real hard and flopped over and slid down the hill," Dennis O'Neil told NBC.
Passenger Frank Tatulli, who was in the first car, told television station WABC the train was travelling much faster than usual.
"The guy was going real fast on the turns and I just didn't know why because we were making good time," he said.
New York City Fire Commissioner Salvatore Joseph Cassano has said if the New York commuter train had derailed on a workday and was at full occupancy, the result would have a been "tremendous disaster".
New York State's Metropolitan Transportation Authority said the train was about half full, with approximately 150 passengers on board at the time of the crash.