The road, more than simply a system of regulations and designs, is a place where many millions of us, with only loose parameters for how to behave, are thrown together daily in a kind of massive petri dish in which all kinds of uncharted, little-understood dynamics are at work. There is no other place where so many people from different walks of life-different ages, races, classes, religions, genders, political preferences, lifestyle choices, levels of psychological stability-mingle so freely.