One passenger who survived the derailment of a New York City train on Sunday that killed four people announced on Wednesday that she intends to sue the railroad.

An attorney filed a notice of claim - the necessary first step to filing a lawsuit - against the Metropolitan Transportation Authority on behalf of dentist and retired Army colonel Denise Williams, a survivor of the derailment, on Wednesday.

Although an investigation into the incident is still underway, preliminary investigations indicate that the engineer, William Rockefeller Jr., was drowsy and fell asleep while operating the train, failing to apply the brakes when approaching a dangerous curve and causing the train to derail. An NTSB investigation revealed that the train approached the 30-mph turn at 82 miles per hour.

Rockefeller is not named as a defendant in the suit, as New York state law requires that any legal claims alleging negligence must be directed at the railroad, not the train's engineer.

Williams, who was not injured in the incident, is seeking an unspecified amount in damages.