Every day millions of passengers put their lives in the hands of train conductors, bus drivers and the truck drivers who share the road with them. All of these jobs require long, monotonous hours with few breaks in between, which can sometimes lead to drivers falling asleep at the wheel.
When that happens, the results can be catastrophic. While some accidents are caused by simple fatigue, others are caused by an easily diagnosed and treated medical condition called sleep apnea.
Four people died and 63 were injured when a train on New York City's Metro North line crashed outside of the city after the train took a turn too fast and slipped off the rails. The cause of the accident was determined to be the engineer suffered from sleep apnea, which was undiagnosed.
Sleep apnea causes the windpipe to constrict during sleep, waking you up temporarily and preventing deep sleep. Elderly people and those who are overweight are at higher risk.
National Transportation Safety Board member Mark Rosekind said sleep apnea is a national problem with drivers and conductors.
"We have accidents in rail, commercial trucking, commercial aviation, marine, pretty much every mode of transportation," Rosekind said.
Some companies are taking steps to combat this problem. Trucking company Prime has its own sleep lab to screen its drivers for sleep apnea. But so far, there are no nationwide rules to require drivers to be tested, which transportation experts say is a major and dangerous issue.
"One of the biggest problems with that is that many of those people don't know they've got it," Rosekind said.
Former school bus driver Diesha Clay, 30, of Charlotte, North Carolina, was one such driver. Clay was caught on camera falling asleep at the wheel of a school bus full of kids. Clay said she doesn't remember falling asleep, but she was immediately terminated 30 days after the video became public. She was never tested for sleep apnea before or after the accident, until "Nightline" brought her to Carolinas Healthcare System in Charlotte, North Carolina for a test.
"If I do have it, I would be a mixed feeling," Clay said before the test. "I will be happy to know cause then I know what to expect and what I need to do. And then also confused with like, if I would've known before, I don't think I would be in this situation."
To be tested for sleep apnea, a registered sleep technologist monitored Clay overnight, and then Dr. Jaspal Singh reviewed the results with her the following morning. Singh told her she stopped breathing roughly seven times an hour, meaning Clay had "mild to moderate" sleep apnea.
She was given a machine called a CPAP (Continuous Positive Airway Pressure) to wear when she sleeps and help regulate her breathing. Since her diagnosis, Clay has contacted a Human Resources lawyer in the hopes that she may be able to challenge her termination, due to the fact that she had undiagnosed sleep apnea. Clay did not initially challenge her termination.
"To think about the people who don't know they have sleep apnea, it's scary because honestly some people do not know," she said. "For example, like me. I did not know. I didn't have a clue. … In my opinion, I feel like there should be wide testing when it comes to transportation."