Generalizing second order macroscopic models via relative velocity of   disturbances propagation in traffic flow
  In this paper, we present a new approach that generalizes the existing second-order hydrodynamic traffic models. In the proposed approach, we use the expression for the relative velocity of disturbances propagation in traffic flow. We show that properties of any phenomenological model are fully defined by how the relative velocity of disturbances propagation expressed in the model. We verify the proposed approach through simulations of the Interstate 580 freeway segment in California, USA, with traffic measurements from the Performance Measurement System (PeMS). 
Yaroslav A. Kholodov, Andrey E. Alekseenko, Aleksandr S. Kholodov,   Aleksey N. Karachev, Alexander A. Kurzhanskiy
physics.soc-ph