Any screening program that emerges is likely to start with questioning about the subject's sleep habits and some physical measurements. Overnight sleep-observation studies, which can be time-consuming and expensive, could follow.
Apnea robs its victims of rest because their tongue and throat muscles relax too much during sleep, and they are repeatedly awakened as their airway closes and their breathing stops.
"The person basically gasps himself awake," said Dr. Gregory Belenky, director of the sleep and performance research center at Washington State University. "It's very much the functional equivalent of waterboarding."
Loud snoring is a symptom and apnea is more common in those who are overweight. Having a large neck size, over 17 inches for men, is a risk factor.
In the case of engineer William Rockefeller, who was at the controls during the Metro-North derailment, the National Transportation Safety Board said he was classified as obese at 5-foot-11 and over 260 pounds.
Rockefeller told NTSB investigators that he felt strangely "dazed" before his train hit the curve, which has a 30 mph speed limit, at 82 mph. Asked if he was clearheaded enough to realize he was entering a curve, he replied, "Apparently not."
Rockefeller's medical exam after the accident uncovered "severe obstructive sleep apnea," and when experts studied his sleep, he woke up about 65 times an hour without being conscious of it. As few as five interruptions an hour can make someone chronically sleepy.
The Federal Railroad Administration, with the help of Harvard's medical school, has set up a website with resources including an apnea questionnaire and a video of a man snoring thunderously and repeatedly waking up to breathe during a sleep test.
James Stem, a lobbyist with the International Association of Sheet Metal, Air, Rail and Transportation Workers, said the website is useful but nationwide rules are needed.
"Fatigue is the No. 1 safety issue in the industry today," he said.
At Boston's Massachusetts Bay Transportation Authority, anyone hired to drive a bus or a train is screened for sleep disorders using the Epworth Scale, a questionnaire that asks people to rate their chances of dozing off in various daytime situations, including watching TV and driving but stopped in traffic.
"People with sleep apnea, they fall asleep at stoplights, they fall asleep at meetings during the day," Belenky said. "They'll deny any sleepiness and nod off right in front of you."
If the questionnaire leads to a diagnosis, Boston's drivers are required to get treatment and comply with it.
A common treatment of obstructive sleep apnea is CPAP, or continuous positive airway pressure, which uses a mask and hose to push a steady flow of air pressure into a person's airway during sleep. The mask can be programmed to reveal whether a person is following doctor's orders.
At the Chicago-area Metra network, spokeswoman Meg Riley said there's no specific test of engineers for sleep apnea, but if their regular exams lead to a diagnosis, the railroad requires treatment and a doctor's statement that the employee is cleared for work.