The science debunking this overpass safety myth has a lot to do with something called the Bernoulli effect. "If you could imagine, say, taking a garden hose and putting your thumb over it, the water gets a lot stronger going out through that small opening," explained Brooks. "And that's essentially what the tornado does going through that little area of the overpass. It actually acts as a wind tunnel and accelerates the flow through that little tiny area where people are trying to hide."
And many overpasses don't have any place to cling onto, adding to the danger in a strong wind. In a tornado, that wind will carry debris that will collect in the small space of an overpass, increasing the chance that something will hit you. And there's another problem. Vehicles stopped there can clog the road and make it impossible for emergency vehicles to get through.
So what do you do if you are in your car and tornado is coming right at you? Contrary to what you might assume, the experts say the first thing to do is get away from your car. It's tempting to stay where it's warm and dry but, experts say, to be safe, get out of the car, find a ditch or a gully, and get as low as you can. Typically, tornado winds are more violent higher off the ground. And that's another reason you don't want to climb up into an overpass.
Even with airbags and a seat belt, a car is much less safe than a ditch in a tornado, Brooks said. "Cars get thrown 100 yards. And at that point your airbags don't do you a whole lot of good." Twister Sister Peggy Willenburg put it this way: "The car can instantly become a tumbling piece of debris with you in it."
What if you are in your home when a tornado is coming? For decades, people were told to open doors and windows to equalize pressure to prevent the building from exploding. It is advice tornado watchers have been trying to put to rest for years.
"It's more important to take shelter than try open or close windows, because that's not going to make a difference if a tornado hits," said Metz. "It's going to blow those windows apart anyway."
"A tornado will very efficiently open those windows for you," Willenburg added.
Last year a powerful tornado ripped through Greensburg, Kan. Fortunately, Dathel Mucklow and her neighbors already had heard that the advice to open windows was just a myth. She didn't waste time with windows. "I went in this closet and I sit down on this pillow, and I put a pillow over my head," she said.
Across town, Sylvia and Darol Hall ran down to their basement, and got under the stairs just in time. "We figured the stairs was the best place," Sylvia Hall said. They were right, say experts, to get underground and also under the cover of something that can shield you from debris.
Willenburg says if you don't have a basement, "get into an interior and secure room where there aren't windows, because if the tornado hits it's going to blow the windows apart and you don't want shattered glass flying around. Because the debris is what can kill you, not just the winds."
The Halls survived, but their house did not. Ten people died that night in Greensburg, but the number might have been higher if more people had believed the myths.