Friends don't let friends shelter under overpasses during severe weather.
Parking under overpasses blocks the free flow of traffic, cuts off potential escape routes to those without shelter (i.e. unhoused folks living in cars, folks in mobile homes), cuts off emergency vehicle routes, and raises the potential for deadly traffic accidents. Doing this puts not only you but others into a dangerous situation against their will!
Always perform personal risk assessment in severe weather scenarios. Being underground or in a structure with a foundation is the safest place to be during severe weather, specifically in an innermost room or storm shelter if avaliable. The biggest threat in a tornado is the debris, which doesn't come from above, but instead horizontally around the center of rotation. Walls protect you. Overpasses, ditches, and vehicles should only ever be a last resort. If your only choices are between equally bad options, have a plan to have enough information that you are not there when severe weather hits.
Full presentation provided text is summarized from. An old resource, but a good one.
Printouts for storm safety tips
SPC convective outlooks + mesoscale discussions. A bit dense if you're unfamiliar with reading them, but a good resource to have to stay prepared and plan ahead of severe weather. Has toggles for viewing counties, population, local FEMA designations, and tribal land to better orient your location on the map. Day 1 = Today, Day 2 = Tomorrow, etc.