THE BRONX - The Federal Railroad Administration says it has serious safety concerns following Sunday’s Metro-North derailment that killed four people in the Bronx.

The National Transportation Safety Board removed the rail workers union from the investigation yesterday after a union representative said that the train’s engineer was nodding at the controls before the crash.

The NTSB has not yet confirmed that information about the engineer. Officials do say the Metro-North train was going 82 mph in a 30 mph zone when it derailed and that its brakes did not show signs of malfunctioning.

Engineer William Rockefeller is said to be cooperating with investigators.