When it comes to drowsy driving dangers, the National Transportation Safety Board said today that Americans need to wake up.

The NTSB, for the first time, held a forum on drowsy driving in Washington, D.C.

Mark Rosekind, a board member, said one of the biggest problems is that people underestimate just how tired they are.

"Humans are just horribly inaccurate if we have to self-diagnose fatigue," Rosekind said. "That's what allows us to put ourselves in life-threatening situations."

According to the AAA, 40 percent of drivers have admitted to falling asleep at the wheel.

Losing two hours of sleep in just one night can affect a person's reaction time by 20 percent, the NTSB said.

All that can add up to one of the most under-reported problems on the road. One study has suggested that 20 percent of crashes - one out of every five accidents - involves a tired driver.

On test tracks at Virginia Tech, researchers are assessing drivers for alertness and signs of fatigue.

Cameras are also being tested to see whether they can look at a person's face and find telltale signs of a lack of sleep. Some cars have even been equipped with technology that can sense a driver drifting into another lane.

For now though, the NTSB is issuing this bit of advice: If a driver has not had enough sleep, they should not get behind the wheel.

ABC News' David Kerley and Matt Hosford contributed to this report.