For many of us, it's almost as if cars were designed as sleep aid devices: the gentle rocking, the slight vibration of the tires on the road, the perfect temperature control. No wonder, then, that a recent National Sleep Foundation "Sleep in America" poll found that 60 percent of adult drivers say they have driven a vehicle while feeling drowsy in the past year, and more than one-third (37 percent) have actually fallen asleep at the wheel. Besides the obvious danger of being asleep at the wheel, studies show that simply feeling sleepy is akin to driving intoxicated in terms of reaction times, vigilance, coordination, reflexes, and so-on. You know, the stuff you rely on to drive.

Another major safety issue is when you drive. And all the studies show that you're far safer during daylight hours. According to the AAA, the odds of a roadway mishap are five times more likely (20.3 percent versus 4.3 percent) to happen between 11:00 p.m. and 6:59 a.m. than any time during the day. (For the record, most crashes or near misses occur between 4:00 a.m. and 6:00 a.m. and midnight and 2:00 a.m.)