In this file photo, New York Police Department officials use a boat to search the waters around the site of a Metro-North train derailment in the Bronx on Dec. 1, 2013. The Metro-North train derailed, killing four people and injuring 63, including 11 critically. An investigation determined the engineer had fallen asleep. (ADREES LATIF/REUTERS)

Bus drivers, truckers and railroad workers could be tested for sleep apnea, which can cause them to doze off on the roads and rails, under a federal proposal announced Tuesday.

Pilots already are tested for the disorder, which disrupts normal sleep and contributes to drowsiness during the day. Two years ago, the engineer of a Metro-North commuter rail train dozed off, resulting in a derailment in the Bronx that killed four people and injured 60.

“The sooner patients with [obstructive sleep apnea, or OSA] are diagnosed and treated, the sooner our rail network will be safer,” said Sarah E. Feinberg, administrator of the Federal Railroad Administration.

More than 25 million Americans are estimated to suffer from undiagnosed sleep apnea. The risk posed by lack of sleep was underscored last week in an unrelated study by the American Automobile Association Foundation for Traffic Safety, which found that almost one-third of drivers said they had trouble keeping their eyes open when behind the wheel within the past 30 days.

“Fall-asleep crashes are a big problem,” said Nate Watson, president of the American Academy of Sleep Medicine. “The AAA Foundation estimates over 300,000 crashes a year are due to drowsy driving.”

In 2013, according to National Highway Traffic Safety Administration data, more than 1,200 people were killed in accidents caused by someone’s falling asleep behind the wheel. Watson said that up to 90 percent of those who suffer from sleep apnea are unaware they have the disorder.

“The collection and analysis of sound data on the impact of OSA must be our immediate first step,” said Scott Darling, acting administrator for the Federal Motor Carrier Safety Administration.

Tuesday’s announcement could lead to a requirement that railroad workers and commercial drivers be evaluated and treated for sleep apnea. It opened a 90-day comment period that will include public fact-gathering sessions in Washington, Chicago and Los Angeles.

Congress in 2013 required that regulators go through the formal rulemaking process when the influential trucking lobby weighed in on a Federal Motor Carrier Safety Administration advisory that suggested that commercial drivers be tested and treated for the disorder.

“We call upon the public to help us better understand the prevalence of OSA among commercial truck and bus drivers, as well as the safety and economic impacts on the truck and bus industries,” Darling said.

In the aftermath of the Metro-North crash, the National Transportation Safety Board stressed that sleep apnea was a major safety issue. The NTSB suggested it can raise the risk of a motor vehicle accident by up to seven times and said that in the past 15 years, sleep apnea may have resulted in a dozen accidents, including four involving railroads.

The FRA asked the federal safety agency to use that accident as a case study. The Metro-North engineer, William Rockefeller, apparently fell asleep at the controls. He recently had been moved to a different shift and later was diagnosed with sleep apnea. Metro-North examined 320 engineers and determined that about 18 percent of them had sleep apnea.

The disorder results in reduction or cessation of breathing during sleep. In one study, the American Academy of Sleep Medicine found that for people who suffer from sleep apnea, eight hours of sleep can be less refreshing than four hours of ordinary, uninterrupted sleep.

The FAA reported last year that more than 4,900 licensed pilots were being treated for sleep apnea.

The NTSB determined that it was a contributing factor in 2008 when both the captain and co-pilot fell asleep on a Mesa Airlines flight bound for a Hawaiian island. The plane flew 26 miles past the airport and out across the open ocean before a radio call from an air traffic controller awakened the crew.

Watson said that a study of commercial drivers found a 73 percent reduction in preventable accidents among those being treated for sleep apnea.

Treatment involves sleeping with a device that covers either the nose or the nose and mouth, and pushes in humidified room air.

“It’s like a balloon that pops the airway open and allows the patient to breath effectively in their sleep,” Watson said. “We also encourage weight loss. Every 1 percent loss in weight can reduce sleep apnea by 3 percent.”

The FRA also is working with railroads on regulations to establish fatigue management plans.