A sleep-deprived person behind the wheel or in the cockpit is just as dangerous as a drunken driver.

That’s one of the conclusions scientists have reached after years of study on sleep — and what happens when people don’t get enough of it. Scientific understanding has improved with a surge of research on sleep apnea, internal body clocks, reaction time and the judgment of the sleep-deprived.

But U.S. transportation guidelines lag far behind the science.

Over the past four decades, more than 320 accidents and incidents have taken nearly 750 lives in airplane crashes alone in which fatigue was cited by investigators as a factor.

The National Transportation Safety Board, created in 1967 to help safeguard travelers, has been trying to persuade federal agencies, industries and states to take steps to reduce these kinds of accidents. The board has issued 138 fatigue-related safety recommendations. Only 68 have been implemented, according to the analysis.

Some of the proposals are still pending decades later. In other cases the board has simply given up, declaring recommendations to be “closed unacceptable.”

That's one conclusion of an analysis by News21, a college journalism coalition, and the Center for Public Integrity, a nonprofit investigative journalism organization. (Many of their stories are being published this week by msnbc.com. You can read the full series at News21.)

Monotony

Accidents happen in a matter of seconds. An airplane pilot takes a moment too long to react in an emergency. A trucker who has been on the road all day wanders across the median. A train engineer, lulled by the isolation and monotony, misses a signal.

Buses still don't have data recorders to track the drivers' hours of service. The "rest time" for airline pilots still includes their time going to and from the airport and through security. Trains still aren't equipped with systems to detect an engineer's lack of movement.

Restrictions on the number of hours that airline pilots can fly haven’t changed significantly since the 1930s, although they are under review. Regulations governing truck and bus drivers were only recently updated, and those changes might be temporary due to legal challenges. And the U.S. Coast Guard has failed to act on at least six NTSB recommendations to limit the hours of crews on cargo ships, oil tankers, ferries and other commercial ships.

The barriers are partly bureaucratic, and partly cultural. NTSB investigator Malcolm Brenner said public attitudes toward fatigue are about the same as attitudes toward drinking and driving 20 years ago.

“At one time, there was a sense that if you’re under alcohol you can power your way through it, but that’s no longer tolerated,” Brenner said.

NTSB board member Robert Sumwalt said, “We need to quit talking about fatigue and we need to start trying to do something about it."

Jim Hall, former chair of the NTSB, said it’s shocking that U.S. agencies that oversee air, rail, water and highway safety all have failed to reflect the scientific evidence in their regulations.

Transportation Department officials say they are working to clear backlogs and ease delays. Deputy Transportation Secretary John Porcari heads a new DOT Safety Council that has cleared more NTSB recommendations in 2010 than in any of the previous five years, according to the department.

Jill Zuckman, director of public affairs for the U.S. Department of Transportation, said in an e-mail that some NTSB recommendations are impractical or impossible to implement. For example, she said, the NTSB "once recommended that the FAA develop a direct warning system about potential runway collisions for pilots in the cockpit. However, the technology did not exist when the board made that recommendation and still does not exist. … The bottom line is that when it comes to NTSB recommendations, there is often much more to it than meets the eye."

David Castelveter, vice president of communications for the Air Transport Association, a trade group that represents the major airlines, said some safety measures aren’t worth the cost. For example, when the FAA studied a NTSB recommendation to force airlines to require young children to be placed in safety seats in airplanes, the agency came to a surprising conclusion: "If parents were forced to buy seats for their children, some would have to drive instead, and the accident rates for cars is much higher than for airplanes," he said.

The FAA has to "balance the interests of the airlines, the manufacturers, the suppliers, the people who fix the planes and the people who fly the planes," he said. "It’s not just as simple as the NTSB says, ‘Do it,’ so let’s do it."

Many of the NTSB recommendations that have been implemented tend to be modest, such as handing out brochures about fatigue or requiring pilots to sit through a 30-minute training video. Meanwhile, major areas of safety regulation have gone unchanged for decades. A regulation that pilots can fly no more than 1,000 hours in a single year hasn’t changed since 1935.

That was the year that a Washington-bound TWA flight carrying 11 passengers plummeted from the sky and crashed into a muddy field outside of Atlanta, Mo. The pilot and four passengers, including U.S. Sen. Bronson Cutting of New Mexico, died.

In a memo about the crash investigation, Department of Air Commerce Director Eugene L. Vidal called for a government study of fatigue. The letter is the first known mention of fatigue as a concern in aviation safety.

Fifty-five years and dozens of government studies and reports later, the NTSB listed fatigue on its inaugural “Most Wanted” list — recommendations that the safety board believes are the most critical. Today, fatigue remains on the list, one of just four of the original items that have never been addressed to the board’s satisfaction.

Tired — or impaired?

Sleep research shows startling similarities between the workplace performance of people who are fatigued and those who are intoxicated.

Someone who has been awake for 24 hours performs at the same level as someone who has a 0.10 percent blood-alcohol content, high enough to qualify as a drunk driver in all 50 states, according to studies conducted in Australia, Switzerland, Austria, England and other countries.

Steven Hursh of the John Hopkins University School of Medicine, who has studied fatigue for more than 30 years, found that tired pilots take longer to react and suffer from attention lapses. They may lose their ability to keep track of multiple tasks at one time, and they do a poor job of assessing risk, making decisions they would consider too dangerous if they weren’t so tired.

“Temporarily, a person who otherwise is very experienced, very well trained, very, very good at what they do — fatigue can make that person stupid,” Hursh said.

When tired, people react more slowly, struggle with attention lapses and take more unnecessary risks. They also suffer from a narrowed field of focus, or tunnel vision, which limits their ability to competently monitor several things at once — such as the many gauges, switches and control settings of a modern commercial airline cockpit.

What’s most dangerous is that people are unable to recognize their own fatigue.

“By the time you feel sleepy or talk about being sleepy, you’re very far gone,” the NTSB’s Brenner said. “You don’t realize how impaired you are. The part of your brain that recognizes what’s happening is impaired.”

The problem is compounded by a culture “that places a lot of value on burning the midnight oil,” said NTSB fatigue transportation research analyst Jana Price.

Many people take pride in working through fatigue, considering it a sign of strength, even if means putting themselves or others in danger, she said. It’s common to hear people brag about how little sleep they got before getting behind the wheel to drive to work in the morning or how late they stayed in the office to finish an important project.

Anyone who gets less than eight hours of sleep is not operating at 100 percent efficiency, said Scott Shappell, a Clemson University professor and director of the school’s Human Factors Institute.

“We’re all walking around with sleep deficits,” he said. “The joke is always: ‘My 90 percent is better than most people’s 100 percent,’” he said. “Well, that’s fine, but it’s not very funny when we have dead people.”

Fatigue is frequently cited by accident investigators as a factor in accidents in the air and on the water, railways and highways.

On the road

NTSB does not track fatigue-related highway accidents on a regular basis. But in 1993, the board commissioned a study expecting to learn about the effects of drugs and alcohol on trucking accidents. Investigators studied all heavy-trucking accidents that year and made an unexpected discovery: Fatigue turned out to be the bigger problem.

The study found 3,311 heavy truck accidents killed 3,783 people that year, and between 30 percent and 40 percent of those accidents were fatigue-related.

“Truck drivers drive more hours in a week than pilots fly in a month,” said Jacqueline S. Gillan, vice president of Advocates for Highway and Auto Safety. “Drivers are paid by the mile — that’s an incredible incentive to drive as far and fast as you can.”

The NTSB also found that more than half of all single-driver trucking accidents occurred in the earliest hours of the day when the fewest number of cars are on the road: between 2 a.m. and 6 a.m. Three-fourths of those early morning accidents were found to be fatigued-related.

NTSB has issued 34 recommendations regarding fatigue on the nation’s roads. Only 17 have been followed. One of the outstanding recommendations is a call to equip buses with data recorders that can track drivers’ hours of service.

On a dark and desolate stretch of highway in the Four Corners region of Utah in 2008, a busload of skiers were returning from a three-day trip to the slopes of Telluride, Colo. Five hours into a long drive to Phoenix, the 71-year-old driver let his bus wander outside the lines of the two-lane highway.

At about 8 p.m., the bus hit the guardrail, slid down an embankment and rolled into a drainage ditch. The 360-degree roll peeled the top off the Astro Stage Lines Motor Coach and tossed all but three of the 53 occupants into a snow-swept January night. Nine were killed, including five under age 18. The NTSB determined that driver fatigue played a key role in the accident.

Dr. Richard O’Desky, an Ohio physician in occupational medicine who often examines and certifies truckers, said he speeds past trucks on the highway because he knows how often drivers are impaired.

“My problem now is I know too much — the last place I want to be is next to a truck,” he said. “There are plenty that have no business being behind the wheel.”