Just a guess -
people employed by the school board to drive school buses evacuating themselves and their families.
Well, that begs the question: Why were they all in a convoy? Are you saying they all got together and evacuated their own individual families in an organized manner? I don't think so.
The only thing that makes sense is that they were ordered to save the school buses from the impending flood.
Hey, I know! Maybe they were going to all those safe, water-stocked shelters to bring all the indigent people back that they had evacuated. No, wait....