This is fascinating:
When designers try to maximize the number of cul-de-sacs in an area, they create a dendritic—or treelike—system of roads that feeds all their traffic into a few main branches. The system makes just about every destination farther away because it eliminates the most direct routes between them. Connectivity counts: More intersections mean more walking, and more disconnected cul-de-sacs mean more driving. People who live in neighborhoods with latticeworklike streets actually drive 26 percent fewer miles than people in the cul-de-sac forest.