In May 1999, under one Oklahoma overpass, an estimated 12 people tried to take shelter from a tornado.
Only one person died. Her body was found two weeks later buried under six feet of debris. The tornado plucked her from underneath the bridge, along with every last blade of grass from the embankments, and deposited it all in a ditch. The others taking shelter suffered horrendous injuries: Compound fractures, missing fingers, ears and noses ripped off. Some were impaled by flying shingles and 2×4 boards.
Overall three people died in overpasses during that tornado; others were injured for life. The Federal Emergency Management Agency is trying to get the word out that highway bridges are never safe during tornados. Part of the problem with that message is the widespread belief that overpasses offer some safety. This is partly of the natural urge to seek shelter; partly because of news reports of a few very lucky people who happened to survive.
Overpasses appear to be strong shelters from the street view, but they rarely, if ever, are. Most people assume they can crawl in a space at the very top of the embankment, underneath the road above. But overpasses have very little room at the top, sometimes no ledge at all, leaving people in an unsteady position at the top. It isn’t obvious to shelter seekers that overpasses usually have no handholds: No girders or beams, just smooth concrete.
Once in this precarious shelter, people are actually in the worst possible position: They are trapped in an elevated space where winds will be stronger than on the ground. Overpasses become wind funnels, channeling violent, shifting winds exactly to the location of the so-called shelter. Instead of being sheltered, they are actually bombarded by winds carrying debris so vicious that it can reduce a large tree to toothpicks. Finally, by stopping on the road and taking shelter in an overpass, a few people endanger everyone on the road. In the worst recorded tornados, cars under a bridge completely blocked the road, leaving hundreds of drivers with no way to escape.
So what should drivers do?
Don’t drive in violent weather. Find any stable building and stay there. Even in the most violent tornados, people who stay inside are always safest, according to FEMA. If you are on the road, and can observe the direction of a tornado, you can drive at right angles to it. This advice has been removed from the National Weather Service guidelines, but it is better than sheltering in an overpass. If you have no other options, get out of your car. Lay flat in a ditch. The winds will be weakest on the ground. Cover your head. Don’t stay in the car.