I was unconsciously humming a pleasant little tune when a woman in the next line started humming a line of harmony. We laughed. We couldn't figure out where it was from, but a young man who was bagging groceries knew immediately -- it was the theme to "Sonic The Hedgehog."
American Indian children, from the age of three on, are taught using a "talking stick" to practice the art of listening and respecting another's viewpoint. So why not try the same method in your carpool?