WASHINGTON - The NTSB released a preliminary report on last month's deadly Metro-North derailment in Spuyten Duyvil, but an official cause of the crash has yet to be determined.

The report confirms the train was traveling an estimated 82 mph on a 30 mph curve before it went off the tracks, killing four people and injuring 59. The NTSB says the train conductor reportedly fell asleep behind the wheel.

The report rules out any malfunctions of the train's signal, brakes or other mechanical equipment. Transcripts of interviews with train crew and first responders will be available in a public docket, but the NTSB says that won't be released for another few months.

An NTSB spokesperson says a conclusive report featuring an official cause of the crash likely won't come out until 2015.