Recently Aw Rascle and Zhang introduced a second order model (ARZ) 
that does nor exhibit the usual drawbacks of this family of models, 
i.e. negative velocities and/or densities. The presentation will focused on
the theoretical discussions, the improvement and the complete
resolution, in homogenous case, of the ARZ model followed by the
analysis of the inhomogeous Riemann problem which is shown to be
equivalent to the inhomogeous Riemann problem for a related first
order model with modified equilibrium flow density relationship. The
boundary conditions for the ARZ model are deduced and can be
expressed in terms of an upstream demand and downstream supply.



Talk