I'd suggest that there be an age-appropriate unit within the school to explain to the children the basics of global warming and pollution from cars -- for instance, that driving an SUV on a 40 mile daily commute puts 12 pounds of carbon into the air.  The point here isn't to demonize SUV's or scare anyone, but rather to give the students a small amount of information and a balancing opportunity to take action, i.e., to get across to them that one student/one car is bad for the earth.  This would take carpooling out of the realm of "personal virtue" on the part of the parents, and turn it into something like a competition among the students, so that it becomes a moral norm to carpool with at least one other student.  Aside from immediately cutting the amount of morning/afternoon traffic in half, this would have the added benefit of showing the kids, before or as they start to drive, that carpooling and mass transit are the way to go, and that the driving habits of the past (one person/one car) are uncool."

I think this suggestion would help to reduce global warming emissions, and maybe even most importantly make the students aware of the necessity of changing the way we live in order to make sure that we all have a habitable planet to live on in the future -- and make them feel empowered by being the driving force in making that change (through finding carpool mates).  This kind of change in moral norm, including a demonstration that we can make a difference on a personal level, is exactly what's needed, immediately -- both to reduce Mulgrave's traffic problems, and to make the kids part of a global solution, which seems to be such an important part of the Mulgrave curriculum in other ways.