you into the fog on a highway in virginia where 95 cars and trucks slammed into each other, one after the other, 95. Abc's david kerley wants to show you what to do if you're driving and the fog... See More
you into the fog on a highway in virginia where 95 cars and trucks slammed into each other, one after the other, 95. Abc's david kerley wants to show you what to do if you're driving and the fog closes in. This is crazy. Reporter: A striking scene. Is anyone up there bleeding? Reporter: Cars and trucks -- crushed. This man crawling out of his overturned van. A mile-long mess. 17 different pile ups, some ending in fire. It was the middle of the day. Three dead, two dozen hurt, on a mountainous interstate where fog, this time of year, is notorious. When the seasons change, with cold and warm air colliding -- fog. And look in the rearview mirror, this man stopped at a light -- the car behind swerves, and side-swipes him. You know, motorists really can underestimate fog because they see it all the time. This is part of their daily life. At the same time, you don't give it the respect that you should. Reporter: In 2011, 20,000 accidents involving fog, in this country, which killed more than 350 people, and injured 10,000. We used a fog machine to simulate conditions. And conditions can change quickly. Right now, I can see that cone clearly. But if a fog bank rolls in, it disappears. If it was a parked car, I would never see it. It's like driving blindfolded. What can you do? Reduce your speed, and watch your speedometer. Because fog gives an illusion slow motion. Use low beams or fog lights. Because high beams just reflect off the fog, making it even harder to see. Shut off the radio, and lower your window a bit so you can listen for traffic. California has gone so far to create a public service campaign. Fog kills. Slow your pace. It's not a race. Reporter: A deadly lesson again -- in the mountains of southwest virginia. David kerley, abc news, washington.
This transcript has been automatically generated and may not be 100% accurate.