Nighttime driving is risky. In 1994, there were more than 2 million nighttime collisions in the United State, more than 18,000 of them were fatal.

Inexperienced drivers fare especially poorly at night. More than half of all motor vehicle deaths involving teenagers occur between 9 PM and 6 AM. Pedestrian deaths also are highest during those hours.

What makes nighttime driving so dangerous?

Vision

With their headlights on, drivers usually can see a small portion of the road ahead of them. However, their peripheral vision isn't as sharp. In addition, darkness makes it more difficult to gauge distances and movement. And the headlights of other cars can create a blinding glare.

Some drivers have "night blindness" caused by a defective retina or a vitamin-A deficiency. But no states test for night blindness during vision tests for driver license renewal.

Age

Night vision gradually begins to deteriorate in your 20s. As you age the amount of light that is admitted into your eyes decreases. The light that does get into your eyes scatters more creating a hazy glare at night.

For every 15 years of life, the amount of light admitted to the eye is cut by as much as half. That means that the average 60 year old needs three times as much light at night as the average 20 year old.

Alcohol

Despite aggressive anti-drinking and driving programs, alcohol remains a significant factor in nighttime crashes. In 1994, some 60 percent of the drivers killed in crashes between 9 PM and 6 AM were legally drunk.

Alcohol and night driving are especially lethal for young drivers. Almost half the fatal nighttime multiple-vehicle collisions that involve teens are related to alcohol.

Fatigue

Exhaustion dulls drivers' concentration and slows their reaction time. And the later it gets, the wearier drivers become. Drivers are least likely to be alert between 3 AM and 7 AM. Fatigue also is likely to set in at a driver's normal bedtime. Alcohol also worsens fatigue.

(Adapted with permission from Safety + Health, Published by the National Safety Council, 1121 Spring Lake Drive, Itasca, Illinois 60143-3201, October, 1996.)