If you're distracted or drowsy while driving, you're more likely to be in an accident than are people who pay attention to the road.

To discover that, researchers from the Virginia Tech Transportation Institute, working with the National Highway Transportation Safety Administration, just spent $4.1 million over a 13-month period.

It might seem that Captain Obvious is striking again, but this time he has excruciating documentation.

The "100-Car Naturalistic Driving Study" placed tiny cameras and control sensors in 100 vehicles driven by 241 volunteers in the Washington, D.C., area. In a little more than a year they racked up a total of almost 2 million miles, 82 crashes and 761 near crashes -- all caught on 42,300 hours of video.

Researchers then studied the data to determine what drivers do to increase their risk of an accident.

The results confirm -- but with more detail -- what seems like common sense: Multi-tasking while driving is dangerous, and the more tasks, the more danger. Further, younger drivers are more likely to engage in that kind of multi-tasking.

"This study is the first to assess which types of behavior contribute most to crashes and near crashes," said Charlie Klauer, one of the researchers involved in the study.

She suggested that a nationwide project be done to gather more data under different circumstances, such as rural driving. That kind of project would cost significantly more than the 100-car study, but could reveal unexpected information the way the VTTI study did.

"The biggest surprise was the prevalence of drowsiness during daylight hours," said Tom Dingus, VTTI's director. Researchers did not expect people to be sleepy during their morning commute, he explained.

Another shock: "The degree to which younger drivers [18 to 34 years old] were willing to engage in secondary tasks at any time." Dingus said that the younger the driver, the less they seemed to care about traffic conditions. Older drivers tended to wait until traffic was light before dialing the phone or messing with the radio.

While the more experienced drivers may have felt safer waiting for that empty road, some learned the hard way that it was still risky. In one video released to the press, a driver who appears to be in his 30s drives off an empty road while removing a CD from its case and inserting it into the player.

Other revelations from the study:

In 93 percent of rear-end collisions, driver inattention played a role.

Drowsiness contributed to one in five accidents, but may be underreported; drivers don't always tell the police they were tired when they crashed.

People older than 34 are better drivers; younger people had four times as many inattention-related crashes and near crashes.

The more "multiple-movement actions" you try to do -- dialing a seven-digit number, unwrapping and eating a burger, etc. -- the greater your chance of being in an accident.

The study also found that it isn't always gadgets that are to blame. "Technology, of course, is not the only distraction," said Jacqueline Glassman, acting administrator of NHTSA. While cellphones were the most common distractions, eating, reading and putting on makeup are also dangerous, she said. One video even showed a woman narrowly avoiding an accident after simply looking down at her lap for a couple of seconds.

And sometimes those distractions aren't even in the car. Another video shows a young woman rear-end a car while she looks at something out her side window. In another, a young man seems oblivious to the fact that his lane is being closed by traffic cones; he takes out several before moving over.

The good news from the study? "Very simple tasks -- those that require only one button -- really don't elevate crash risks at all," Dingus said. Dialing a 10-digit phone number or fiddling with a map, though, are another story.