Hail fails at fast speeds, and it can cause injury to those in its path.
Stop driving and pull to a safe place so hail doesnt break the windshield or any windows, driving compounds hail impact with your car. Stop under a overpass, and dont forget to pull out of traffic lanes and onto a shoulder. Avoid ditches due to high rising water.
Keep your car angled so that the hail is hitting the front of your car. Winshields are reinforced to withstand forward driving and pelting objects.