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.
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Find out what to expect from the weather if you are running in the big race in London or watching from the sidelines.
It will be a soggy start to the weekend and temperatures will drop making it feel colder than in recent days.