Most people think the best thing to do is to take shelter under an overpass or get out of the car and into a ditch or lower ground. But NOAA and the Red Cross do not recommend these as the safest courses of action.
"Highway overpasses are not tornado shelters, and should be avoided," NOAA road safety guidelines state. "Ditches, culverts and ravines should be used only as an absolute last resort. You will be exposed to flying debris, rain and hail, lightning and extreme wind."
If you can see the tornado in the distance, NOAA recommends changing course and driving toward a sturdy shelter as soon as you are able. They recommend truck stops, convenience stores, restaurants, and even walk-in coolers. Once you are inside, go to the basement, a cellar, or a hallway or room without windows in the center of the house.
However, they warn you not to take shelter in a high-risk structure like a mobile home. Your car is safer than a mobile home, the Red Cross states in their safety brochure.
It is possible to try to get out of the tornado's path, NOAA says, and you may be able to stop and allow the tornado to pass, depending on where it is and how you're positioned. If you can see the tornado far in the distance and can determine its movement, drive at a right angle to that movement. So, if it's heading east, drive to the south.
If the threat is immediate and you're stuck in heavy traffic and there's nowhere for you to go, it's time to duck and cover in a ditch or low spot. In that case, NOAA recommends getting as far away from your car as possible.
If the tornado is imminent and you are forced to stay in your car, the NWS recommends keeping your seat belt on and making sure your head is covered, below your windshield and windows to protect it from glass. The Red Cross recommends covering your head with a blanket, if you have one in the car.
Additionally, crowding under an overpass can block traffic and prevent important emergency vehicles from aiding affected areas, NOAA notes. It also cuts off potential escape routes from the tornado.