Dynamics of Traffic Congestions from Large-Scale Data in the Taiwan Highway System*

The Taiwan Highway System has the longest electronic toll collection (ETC) freeway mileage in the world. There are 300 sensors installed on the two North-South spanning highways. The collected data consists of the time information of individual vehicles passing through ETC sensors along their highway journeys. Highway segments are demarcated by successive sensors, enabling us to extract a tremendous volume of dynamical segment-wise data. We trace the evolution of the system on the so-called fundamental diagram with vehicle flux versus vehicle density during traffic congestions in segments, and show that congestions are characterized by loopy trajectories in the diagram. By considering the area enclosed by a loop, we find that there are two types of congestion dynamics -- moderate flow and serious congestion. They behvae differently in terms of the area enclosed. Data extracted from the time delays of individual vehicles show that the area enclosed is a measure of the economic loss due to congestion.