The Riemann problem for a traffic flow model

A traffic flow model describing the formation and dynamics of traffic jams was introduced by Berthelin et al. [ "A model for the formation and evolution of traffic jams, " Arch. Ration. Mech. Anal. 187, 185-220 (2008)], which consists of a pressureless gas dynamics system under a maximal constraint on the density and can be derived from the Aw-Rascle model under the constraint condition rho <= rho* by letting the traffic pressure vanish. In this paper, we give up this constraint condition and consider the following form:{ rho(t) + (rho u)(x) = 0 , (rho u + epsilon p (rho))(t) + (rho u(2) + epsilon up(rho))(x) = 0 , in which p(rho) = - 1/rho. The Riemann problem for the above traffic flow model is constructively solved. The delta shock wave arises in the Riemann solutions, although the system is strictly hyperbolic, its first eigenvalue is genuinely nonlinear, and the second eigenvalue is linearly degenerate. Furthermore, we clarify the generalized Rankine-Hugoniot relations and delta-entropy condition. The position, strength, and propagation speed of the delta shock wave are obtained from the generalized Rankine-Hugoniot conditions. The delta shock may be useful for the description of the serious traffic jam. More importantly, it is proved that the limits of the Riemann solutions of the above traffic flow model are exactly those of the pressureless gas dynamics system with the same Riemann initial data as the traffic pressure vanishes.