Federal investigators could be on the scene of a deadly train wreck in New York City for up to ten days as they try to determine what caused the crashed the killed four people and injured 63 more passengers.

“I think it's fair to say that tomorrow, people who use this line should plan on a long commute or plan on using the Harlem line,” New York Governor Andrew Cuomo said on Sunday.

The crash happened at 7:20 AM in a wooded area where the Hudson and Harlem rivers meet, about a hundred meters north of a station in the northern Bronx borough.  It was half full at the time – light ridership on the weekend is probably he only fortunate thing about it.

“On a work day, fully occupied, it would have been a tremendous disaster,” said New York City Fire Commissioner Salvatore Joseph Cassano.

Trains have to slow down for sharp curves at the scene of the crash.  Investigators will focus on track conditions, signaling systems, mechanical equipment and the performance of the train crew.  They also have the “black boxes” data recorders, similar to those installed on passenger jets, so they’ll know how fast the train was going and whether the operator applied the brakes correctly, or at all.