Seeking Shelter: 5 reasons why overpasses are a terrible idea

Imagine driving down the interstate as the sky turns dark. You come over a hill and see a tornado ahead of you. What do you do?

An EF-4 tornado just before it crossed Interstate 39 in Northern Illinois on April 9, 2015. Photo by KFOR-TV stormchaser Reed Timmer.

Instinctively, you may think "I've got to get under something!" But today, we have five good reasons you should think twice.

  1. Highway overpasses offer no shelter from flying debris. The wind in a tornado isn't what injures and kills people, it's the debris moving in the tornado. A weaker tornado can still produce winds in excess of 100 m.p.h.
  2. A tornado's wind speed increases with height. Climbing above ground to situate yourself under an overpass actually puts you at greater risk for fast-moving debris.
  3. As a tornado comes in contact with a bridge overpass, the wind is channeled around the contoured land mass near the approaches to the bridge. This "wind tunnel effect" can increase the velocity of wind under the overpass.
  4. Typically, the underside of highway overpasses are free of anything to hold onto. Anyone subjected to even a weak tornado's wind could be sent flying. It's a poor choice, even as a last resort.
  5. Tornadoes don't produce wind moving in a straight line. A swirling nature of a tornado's vortex means anyone under an overpass will be subjected to a 180-degree change in the wind direction...all in a matter of a few seconds.

Back in 1991, a group of people escaped injury by hiding under a bridge overpass and it was caught on camera. Unfortunately, this led people to believe they were doing the right thing.

So where should you go during a tornado when no safe shelter is present? Looking back at #2, you can start think about places that are as low as possible. Underneath concrete tubes/culverts that go under the highway are the best places if you're away from a reinforced building. Staying in your vehicle is not a safe option, even with some arguments in the past few years suggesting it so.

-Meteorologist Eric Sorensen

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