Sometimes, it's a little scary to find out just how wrong the folk wisdom you've picked up over the years really is. Growing up in Kansas, I remember adults telling me that, if a tornado happened and I was in a car on the highway, I should hide under an overpass. Turns out, that advice is not just incorrect, it's potentially deadly. And it's also a great example of why anecdotes aren't the same thing as data. Why? Because the myth actually stems from one incident in the early 1990s, when people did survive a tornado by seeking shelter under an overpass. But, as the National Atmospheric and Oceanographic Administration explains, those folks were lucky. Very lucky.
The idea that overpasses offer safety probably began in 1991, when a television news crew and some citizens rode out a very weak tornado under an overpass along the Kansas Turnpike. The resulting video continues to be seen by millions, and appears to have fostered the idea that overpasses are preferred sources of shelter, and should be sought out by those in the path of a tornado. In addition, news magazine photographs of people huddled under an overpass with an approaching tornado imply that this is the correct safety procedure. Nothing can be further from the truth!
In the Oklahoma City area in May, 1999, three people were killed and many had serious injuries by a violent tornado while seeking shelter under an overpass. Eyewitness accounts from others in the area indicated that roads were blocked at times as people stopped cars to run up into small crevices under an overpass. Not only is the overpass unsafe as a shelter, blocking roads denies others the chance to get out of the storm's path, and impedes emergency vehicles from their critical duties!
Wind speeds in tornados can be over 200 mph. These destructive winds produce airborne debris that are blown into and channeled under the overpass where people might try to seek shelter. Debris of varying size and types, including dirt, sand and rocks, moving at incredible speeds can easily penetrate clothing and skin causing serious injuries and possibly death. Very fine debris can also be forced into eyes causing injury or loss of sight. A person could even be blown out or carried away from the overpass by the fierce tornado winds. People positioned at the top of the overpass encounter even high wind speeds and more missile-like debris. Wind direction will also shift abruptly as the tornado passes tossing debris from all sides.
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.