Four people were killed and nearly 60 injured in the crash, which took place along a sharp curve near the Spuyten Duyvil Station in Bronx, NY. The train was traveling 82 miles per hour at the time — in an area with a 30-miles-per-hour limit.
A post-accident sleep study found that the engineer, William Rockefeller, suffers from severe sleep apnea, the report states. A toxicology report determined that he also had traces of an over-the-counter antihistamine in his blood at the time of the crash.
The medicine carries an FDA warning that states, "may impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery)."
Rockefeller told a union official that he nodded off just before the derailment, according to a report by CT Mirror.
Rockefeller had undergone five physical exams between 1999, when he started working for Metro-North at the age of 32, and 2011. At no point during those exams did he or his doctors document any sleeping issues, the NTSB report states.
The exams documented repeatedly high cholesterol and a steady weight gain over the years, to the point that his doctor characterized him as "overweight" at his last physical before the crash, on May 3, 2011.
Sleep apnea often goes undiagnosed, according to the National Heart, Lung, and Blood Institute.
"Sleep apnea usually is a chronic (ongoing) condition that disrupts your sleep. When your breathing pauses or becomes shallow, you’ll often move out of deep sleep and into light sleep," the NHLBI states on its website. "As a result, the quality of your sleep is poor, which makes you tired during the day. Sleep apnea is a leading cause of excessive daytime sleepiness."According to the NTSB medical report, the sleep study revealed that Rockefeller had an apnea/hypopnea index (AHI) of 52.5 episodes per hour, and it climbed to as high as 67.5 episodes per hour.
The report states that more than 30 events per hour is considered severe sleep apnea.