what to do when severe weather is forecast

We once stopped at a truck stop for fuel around Oklahoma City. All the truckers were inside gathered around the t.v. We asked what's up. We were told they are watching the tornado warnings. We asked where it's at. We were told "Right Here"!!! Seriously, it had heading right for us. Along with the tornado they were predicting 'grapefruit-sized hail'. That scared us more than the tornado. We saw an overpass from the window; got in the motorhome and went to it. We pulled off the highway and tucked in under the overpass. Soon cars joined us & some were even climbing up the steep slope to park. The hailstorm came but luckily not the tornado which did hit a couple miles away. Later we talked to folks and were told the worse thing you can do is to get under an overpass because a tornado would roar through there. I guess in that circumstance the best thing we could have done was to stay inside the building at the truck stop and forget about the oncoming hail storm. A big decision.