New York, New York -- As people jam the roads and highways over the summer, there's greater risk of being -- or running into -- a drowsy driver, says the National Road Safety Foundation, Inc., a non-profit group that provides free driver safety films and programs including its newest, called "Recognizing the Drowsy Driver."

"A day in the sun can make you tired," says Adele Kristiansson, director of marketing and legislative affairs at the National Road Safety Foundation.

"Drowsiness is a condition most drivers fail to recognize, and it can be as dangerous as drinking and driving," she adds. "Studies show 60 percent of us have driven while feeling fatigued, and more than a third admit to having fallen asleep at the wheel in the past year. Drowsiness is a factor in a substantial number of traffic crashes."

Experts list several signs that should warn a driver to stop and rest:

-- Difficulty focusing, with frequent blinking
-- Daydreaming or not remembering the last few miles driven
-- Head nodding
-- Repeated yawning or rubbing eyes
-- Drifting out of your lane, tailgating or hitting shoulder rumble strips

If you experience any of these warning signs, pull over at the next exit or a safe rest area and take a break or a 20-minute nap. Have a cup or two of coffee or caffeinated snacks and allow 30 minutes for the caffeine to enter your bloodstream. Don't drink alcohol or take medication.

Sleep-induced crashes are often very serious, since the driver does not take evasive or corrective action as he loses control of the vehicle.