Drive on the rim!
If all that's keeping them from civilization is a flat tire, my vote is to drive that rim for all its worth!
shareThat wouldn't matter. You saw the couple's car from the beginning of the film--he peeled it open like a can of sardines. And you know they were driving at high speeds because they veered off and hit a tree during the attack.
He can clearly fly at very high speeds, so if a car going 80mph on the highway has no chance, a bus with flat tires definitely won't. Besides, it's an easy target...big object moving along a (mostly) straight two-lane highway.
Besides, he was just toying with his prey to drum up their fear for the first, few hours. If he wanted to destroy that bus and kill everyone immediately--he would have.