Anisotropic second-order models and associated fundamental diagrams

According to Banks [Investigation of some characteristics of congested flow. Transportation Research Record, 1999], traffic heterogeneity explains the data scattering on the flow-density plane and positive transferences within the congested phase (a transference is a line connecting adjacent points in the time series). This heterogeneity results from a traffic mixture, made up of various vehicles and drivers, or different traffic conditions such as meteorological conditions. This paper only deals with traffic mixture and more particularly with vehicle classes such as passenger car and truck, which are correlated to the vehicle length. When considering a macroscopic model, the mean vehicle length, which is measured by sensors, is associated with the truck percentage. Then the Generic Second Order Model (GSOM) by Lebacque [Generic second-order traffic flow modeling. Proceedings of the 17th International Symposium on Transportation and Traffic Theory, 2007] provides a rigorous mathematical framework for traffic heterogeneity modeling. The added value in this paper is that admissible invariants which characterize generic fundamental diagrams, possibly depending on the mean vehicle length, are interpreted and debated. Aw-Rascle-Zhang's [Resurrection of second-order models of traffic flow. SIAM Journal of Applied Mathematics, 2000] [A non equilibrium traffic model devoid of gas-like behavior. Transportation Research Part B 36, 2002] and Colombo's [A 2 x 2 hyperbolic traffic flow model. Mathematical and Computer Modeling 35, 2002] anisotropic models are deeply analyzed from a traffic point of view. At last an extended GSOM equation system provides a full parameterization of fundamental diagrams which is needed to traffic heterogeneity modeling. (C) 2011 Elsevier Ltd. All rights reserved.