Engineering Seminar Series (Collaboration with CITIES):

Traffic Flow as a Simple Fluid: Towards a Scaling Theory of Urban Congestion

On March 16th, 2023, CITIES, in collaboration with the Engineering department, organized the Engineering seminar series talk “Traffic Flow as a Simple Fluid: Towards a Scaling Theory of Urban Congestion,” presented by Prof. Jorge Laval, Georgia Institute of Technology.

In this talk, Prof. Jorge Laval spoke about the analogy between the theory of phase transitions in simple fluids and vehicular traffic flow that has long been suspected, promising a new level of understanding of urban congestion by standing on one of the firmer foundations in physics. The obstacle has been the interpretation of the thermal energy of the gas-particle system, which remains unknown. This talk proposed the flow of cars through the network as a viable interpretation, where the fundamental diagram for traffic flow would be analogous to the coexistence curve in gas-liquid phase transitions. Thanks to the power-law form of the coexistence curve, it was possible to formalize that the resulting network traffic model belongs to the Kardar-Parisi-Zhang universality class. The scaling relationships arising in this universality class are found to be consistent with West’s scaling theory for cities. It is shown that congestion costs (delays + fuel consumption) scale superlinearly with city population, possibly and worryingly more so than predicted by West’s theory. Implications for sustainability and resiliency were discussed.