  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).
