This article deals with macroscopic traffic flow models on a road network. More precisely, we consider coupling conditions at junctions for the Aw-Rascle-Zhang second order model consisting of a hyperbolic system of two conservation laws. These coupling conditions conserve both the number of vehicles and the mixing of Lagrangian attributes of traffic through the junction. The proposed Riemann solver is based on assignment coefficients, multi-objective optimization of fluxes and priority parameters. We prove that this Riemann solver is wellposed in the case of special junctions, including 1-to-2 diverge and 2-to-1 merge.Due to finite wave propagation speed, it is not restrictive to study a single junction. We define a junction J as the set of n incoming and m outgoing branches that meet at a single point (namely the junction point supposed to be located at x = 0) such that J = n+m i=1 J i · e i where e i ∈ R n+m are unit vectors and the branch J i for any i ∈ {1, . . . , n + m} is defined as follows:] − ∞, 0[, for any i = 1, . . . , n, ]0, +∞[, for any i = n + 1, . . . , n + m.In the remaining, we will mainly focus on the cases of a 1-to-1 junction (n = m = 1), a merge (n = 2 and m = 1) and a diverge (n = 1 and m = 2).