Figure-Eight Hysteresis Pattern in Macroscopic Fundamental Diagrams for Urban Freeway Network in Beijing, China

This paper presents Macroscopic Fundamental Diagrams (MFDs) for an urban freeway network in Beijing, China. In the diagrams, a figure-eight hysteresis pattern is clearly observed. To understand the causes, analyses are made ranging from spatialtemporal heterogeneity of vehicles to the flow-occupancy relation for individual locations. As a result, we observe at individual locations that free-flow traffic with the same occupancy exhibits different flows in the onset and offset of congestion; it is attributed to the figure-eight hysteresis pattern at the macroscopic level. The formation of the multi-branch flow-occupancy diagram at individual locations is discussed and explained. The paper enriches the knowledge about MFDs and provides some empirical support for the existing theory.