The dynamics of traffic congestion: Data from a freeway Electronic Toll Collection

Electronic Toll Collection systems installed at regular intervals along freeways provide a tremendous amount of individualized vehicle data useful for traffic analyses and predictions. We demonstrate how real data from the Taiwan freeway system enables us to monitor the evolution of traffic congestions on the fundamental diagram, and find that congestion is characterized by a loopy trajectory such that the area enclosed by the loop increases with the severity of congestion. There is a power law relating the area of the loop to the drop of influx during the congestion period. Data extracted from the time delays of individual vehicles show that the area enclosed by the loop in the fundamental diagram is a measure of the economic loss due to congestion. The use of the loss area to understand various highway characteristics is also explored.