We learn the lessons of traffic control early in life, and with good reason. There are nearly 300,000 traffic signals today in the United States. Each traffic signal performs the task of regulating whose turn it is to go and who must wait. A traffic signal system at its core has two major tasks: move as many users through the intersection as possible and do it with as little conflict between these users as possible. The first task relates to efficiency and capacity while the second relates to safety. Both tasks are performed by first clearly defining which group of users has the right of way at a given time and second by determining how long the group has the right of way.