Traffic Lights

At a normal traffic intersection, you will follow the instructions of the light directly in front of you. Did you know there are seven distinct light cycles that will prevent collisions? Graph theory can find these cycles, by labeling each lane, and connecting traffic-compatible lanes. The resulting graph (the order-4 Möbius ladder graph) can be 4-colored in seven distinct ways. Each coloring gives a different 60-second traffic cycle. Traffic engineers also use graph theory for more complex intersections.