There are times when there is no place else to go. It’s reinforced concrete and steel, offering at least some shelter. Can there be a wind tunnel effect, if the vortex passes directly over that location? Yes. If you were stuck on open highway, had no culvert let alone an underground shelter available to you, and an F4 was bearing down on you, what are you going to do, sit in your car? Suicidal. You take your chances up under the overpass.
Thank you, RC. I will remember your advice.
Regards,