The misconception is that the wind associated with a tornado is confined to within the visible funnel cloud. Unfortunately, a tornado is not a vacuum cleaner hose hanging out of the sky. One possibility why many people think that being under an overpass offers protection is that with something above them, the bridge will prevent the wind from going ‘up’ underneath the overpass. This simply is just not true.
There is no doubt that essentially living at the southern tip of tornado alley we get to see our fair share of destructive tornadoes. Being in your home is one thing, you can take shelter in an interior room. However, what do you do if you are caught out on the road? I know every one’s first instinct is to protect their car and themselves and their first instinct is to take shelter under the nearest immovable object like an overpass. If you know anything about physics, you should rethink this tactic. The fact of the matter is that you may have just made your situation much worse.
Actually, the interaction between a tornado and an overpass is much more like this.
…and here’s a visual reference behind the science.
This is why one of the first and foremost rules in general tornado safety is to get as low as possible, because that is where the wind speed is the lowest! By climbing up underneath the overpass, you are moving into a place where the wind speeds are typically higher. In addition, under an overpass, it is possible in some situations that when air is forced through the narrow passage underneath the bridge, this might cause an increase in the wind speeds (as mentioned earlier). Further, under different circumstances, the area beneath and just downstream of an overpass might become a debris deposition zone, where piles of debris accumulate. Think a hard rain is uncomfortable? Try being pelted with glass, shards of metal, splintered wood, hail and everything else that’s been hurled into the air.
Information from tornadochaser.net
If on a road, hide under an overpass if a tornado approaches.
The sad fact is this idea has caused many deaths of motorists already. The worst thing you can do is hide under an overpass. Winds can actually be worse under an overpass which makes it a bad place to go. Please listen, never use an overpass for protection. See the following document for more info. Overpass deaths report
Open your windows during a tornado?
Scientists once thought that the low pressure in a tornado caused the normal air pressure in
houses to explode out. It turned out that the strong winds from the tornado destroyed the
houses, not the pressure change. If the tornado wants your windows open, it will open them for you.
The southwest corner of a basement is the safest place to go during a tornado.
The best place to go during a tornado is in a center room of the basement, like ones that are usually found under the stairs that lead down to the basement. I was once thought that the SW corner was the best place to go, but it was found the debris collects it the corners which makes it a bad place to go.
Tornadoes can’t cross water or where rivers meet.
Many tornadoes have crossed rivers & lakes, with out any effect to the tornado.
Tornadoes can not cross big hills or mountains.
Tornadoes have made damage paths up and down the side of 10,000 foot mountains, in Wyoming so the hills in eastern Kansas will not protect you.
Tornadoes can’t/don’t hit big cities.
Miami, FL, Nashville, TN, Wichita, KS, Fort Worth, TX, and Oklahoma City have all been hit by tornadoes in the past few years. Take shelter if a tornado warning is issued for your city.
To see what happens when you take shelter under an overpass take note of the people the pass before under the overpass and again after they drove back through.
So far, this has been the deadliest year for tornadoes across the US. North Texas and specifically DFW (none of us forget the tornado that his Fort Worth) are susceptible to extreme weather. It’s my responsibility to make sure that all of you are provided with the best information possible about your car, driving, etc. However, it’s just as important , if not more-so, that you understand the appropriate action to be taken should you ever encounter a tornado while on the road…What you decide to do or not do can potentially have fatal outcomes. I hope you will remember this article if you ever are in this situation.