Undiagnosed sleep apnea led to two commuter train crashes in the New York area, according to the National Transportation Safety Board.
One of the accidents happened in September 2016 in Hoboken, New Jersey. The train didn't stop and ran into the wall of the terminal, killing one person and injuring over 100.
The other happened in Brooklyn in January 2017. A train ran past the end of its line and crashed into the station, causing more than $5 million in damage.
Both engineers in those crashes had undiagnosed, severe obstructive sleep apnea, in which breathing stops and starts during sleep. The disorder can lead to excessive daytime drowsiness.
Additional reporting from Newsy affiliate CNN.