Criticality of Urban Networks: Untangling the Complexity of Urban Congestion

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

This award will support research to explore the application of tools and methods from complexity science to better understand and control urban congestion. This paradigm-shifting approach is made in light of recent empirical data confirming earlier theories that the flow of traffic through urban transportation networks behaves like a fluid inside a container. In this analogy, rush-hour congestion can be thought of as the boiling point of the fluid, where one can observe two distinct states of matter coexisting in different proportions depending on the temperature: gas (little congestion) and liquid (stopped, stuck in traffic). This is where traffic flow becomes chaotic and therefore our traditional engineering tools such as calculus and statistics no longer apply to prediction and control. This research provides a framework for describing and modeling traffic flow systems in this context. The educational component of this project will promote and facilitate the incorporation of basic complex systems education into the civil engineering curricula at Georgia Tech. The theory of phase transitions is one of the better understood theories in physics, but it has not been applied to traffic flow successfully so far due to the lack of a suitable description of heat flow in the system. This project suggests the flow of vehicles as a correct interpretation, and the research approach includes the analysis of large amounts of empirical observations, together with mathematical modeling and theoretical analysis that will combine elements from traffic flow theory, statistical mechanics and fractal geometry within the overall framework of complexity science. Most relevant to this project will be the theory of self-organized criticality (SOC) and its connections with different universality classes such as Manna, Kardar-Parisi-Zhang and directed percolation classes, all of which have received much attention lately in the context of traffic networks. SOC has been found to be fundamental in diverse areas from geology to astrophysics, and this project will explore if urban networks fall in this category, along with the methodological implications for controlling urban congestion. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.