Tornados do not travel in a predictable direction, and some are faster than others.  Usually it is very difficult to determine whether or not a tornado is moving in your general direction.  If you are certain you can safely drive out of the tornado’s path, do so; but do not try to out run the storm.  If you see that the tornado will likely overtake you, take shelter in the nearest building (interior room, lowest level, away from glass).  If there is no nearby building, find a ditch or depression and lie flat, face down, and use your hands to protect the back of your head.  Don’t stay in your vehicle—tornados can toss even large trucks considerable distances.

If you see an overpass nearby, DO NOT consider it as shelter.  Overpasses are very dangerous because they offer no protection from the blast of flying debris in the violently shifting winds of a tornado.  Vital roadways have been blocked by  drivers seeking (futile) shelter.  Read NOAA's report on Highway Overpasses as Tornado Shelters for more information (especially Slide #8).